Evaluating the Quality of Coverage

STK Pro, STK Premium (Air), STK Premium (Space), or STK Enterprise
You can obtain the necessary licenses for this tutorial by contacting AGI Support at support@agi.com or 1-800-924-7244.

The results of the tutorial may vary depending on the user settings and data enabled (online operations, terrain server, dynamic Earth data, etc.). It is acceptable to have different results.

This tutorial requires version 12.9 of the STK software or newer to complete.

Capabilities covered

This lesson covers the following capabilities of the Ansys Systems Tool Kit® (STK®) digital mission engineering software:

  • STK Pro
  • Coverage

Problem statement

You require a quick and easy way to simulate three Earth-observing payloads in three different orbital planes. You need to know when any or all of the satellites' sensors can view the portion of the Earth's surface that falls between 60 degrees north and 60 degrees south latitude. Additionally, you would like to know if any areas of the Earth will be covered by two or three sensors simultaneously, during daylight hours, and if so, for how long. You need to determine the extent and quality of coverage provided by the three satellites.

Solution

Use the STK software's Coverage capability to model and analyze the quality and quantity of coverage provided by the Earth-observing payloads attached to the satellites in the three different orbital planes. Using this model, you will determine if, when, and for how long two or more of the satellites can survey the Earth's surface during daylight hours.

Upon completion of this tutorial, you will be able to:

  • Understand a coverage grid
  • Use constraints in a coverage grid
  • Determine coverage assets
  • Understand multiple Figure of Merit types
  • Choose which data providers supply answers to your questions
  • Create color contours pertaining to the coverage analysis in the 2D and 3D Graphics windows
  • Use the Grid Inspector tool

Video guidance

Watch the following video. Then follow the steps below, which incorporate the systems and missions you work on (sample inputs provided).

Using the starter scenario

To speed things up and allow you to focus on the core aspects of this tutorial, a partially created scenario has been provided for you.

Opening the starter scenario

The starter scenario is included in your install.

  1. Launch the STK application ().
  2. Click Open a Scenario in the Welcome to STK dialog box.
  3. Browse to <Install Dir>\Data\Resources\stktraining\VDFs.
  4. Select Coverage_GettingStarted.vdf.
  5. Click Open.

Saving the VDF as a scenario file

Save and extract the VDF data in the form of a Scenario folder. When you save a VDF in the STK application, it will save in its originating format. That is, if you open a VDF, the default save format will be a VDF (.vdf). If you want to save and extract a VDF as a scenario folder, you must change the file format by using the Save As feature. This will create a permanent scenario file complete with child objects and any additional files packaged with the VDF.

  1. Open the File menu when the starter scenario opens.
  2. Select Save As....
  3. Select the STK User folder in the navigation pane when the Save As dialog box opens.
  4. Select the Coverage_GettingStarted folder.

    5. A scenario folder with the same name as the VDF was created for you when you opened the VDF in the STK application. This folder contains the temporarily unpacked files from the VDF.

  5. Click Open.
  6. Select Scenario Files (*.sc) in the Save as type drop-down list.
  7. Select the Coverage_GettingStarted STK scenario file in the file browser.
  8. Click Save.
  9. Click Yes in the Confirm Save As Dialog box to overwrite the existing scenario file in the folder and to save your scenario.

When saving a VDF as a scenario folder, you should extract its contents to the scenario folder the STK application automatically creates for you in the STK User folder. See the Permanently Extracting a VDF as a Scenario Folder and VDF Setup Considerations pages for more information.

Save () often during this lesson!

Reviewing the starter scenario

The starter scenario contains three previously defined satellites. Each satellite is equipped with a sensor used to model the field of view of the attached data collection instrument.

  1. Click on the 2D Graphics window to select it.
  2. Open the Window menu.
  3. Select Tile Vertically in the shortcut menu.
  4. Look at the objects in the scenario.
    • Earth-observing payloads (Sensor objects) are attached to three different satellites.
    • Shuttle is in a circular orbit with a 51.6 degree inclination.
    • SunSync is in a Repeating Sun-synchronous orbit.
    • TestSat is in a circular orbit with a 70 degree inclination.

    3D View: Three predefined orbits

The Earth-observing mission that these satellites are performing requires the Earth to be in sunlight in order for data collection to occur. You are only interested in the area on the surface of the Earth that falls between 60 degrees north latitude and -60 degrees south latitude.

Inserting a Coverage Definition object

The STK software's Coverage capability allows you to analyze the global or regional coverage provided by one or more assets (facilities, vehicles, sensors, etc.) while considering all accesses. To address area coverage capabilities, Coverage provides you with two STK object classes: Coverage Definition objects and Figure of Merit Objects. Before running a Coverage analysis, however, you must first insert a Coverage Definition object.

While you know what your region of interest is — the portion of the Earth's surface that falls between 60 degrees and -60 degrees latitude — you still need to tell the STK application to use that area as your region of interest. Insert a Coverage Definition object to define an analytical area that will limit itself to user-defined boundaries. Coverage Definition objects enable you to define and maintain an area of coverage, to define the STK objects providing coverage for the area (such as satellites, aircraft and sensors), to define the time period of interest, and to calculate accesses to the region.

  1. Bring the Insert STK Objects tool () to the front.
  2. Select Coverage Definition () in the Select An Object To Be Inserted list.
  3. Select the Insert Default () method in the Select A Method list.
  4. Click Insert....
  5. Right-click on CoverageDefinition1 () in the Object Browser.
  6. Select Rename in the shortcut menu.
  7. Rename CoverageDefinition1 () Stereo_Cov.

Defining a coverage grid

Coverage analyses are based on the accessibility of assets (objects that provide coverage) and geographical areas. For analysis purposes, the geographical areas of interest are further refined using regions and points defined by the STK application. Points have specific geographical locations and are used in the computation of asset availability. Regions are closed boundaries that contain sets of points. The combination of the geographical area, the regions within that area, and the points within each region is called the coverage grid.

Specifying the Grid Area of Interest

Specific results are generated based on detailed access computations performed to user-defined grid points within an area of coverage set by the Grid Definition. The default Grid Definition type is set to Latitude Bounds. This definition results in a coverage region, called the Grid Area of Interest, that is a band circling the globe between your defined latitude boundaries. Refine your Grid Area of Interest to cover -60 degrees to 60 degrees latitude.

  1. Open Stereo_Cov's () Properties ().
  2. Select the Basic - Grid page when the Properties Browser opens.
  3. Enter the following values in the Grid Area of Interest panel:
    4. Option Value
    Min Latitude -60 deg
    Max Latitude 60 deg

Setting the grid resolution

While the area to be considered in the coverage analysis is specified by a set of regions within the defining bounds, the statistical data computed during a coverage analysis are based on a set of locations, or grid points, which span the coverage area. You can determine the spacing between grid points using the options in the Point Granularity panel of the Grid page. These options help you define the fineness or coarseness of the grid. The exact location of the grid points are computed based on a specified granularity.

Finer grid resolutions typically produces more accurate results, but require additional computational time and resources.

  1. Enter 4 deg in the Lat/Lon field in the Point Granularity panel.
  2. Click Apply to apply the changes and keep the Properties Browser open.

Choosing coverage graphics

You can define how the coverage grid is displayed in the 2D and 3D Graphics window using the Graphics Attributes properties for the Coverage Definition object. The fields on the 2D Graphics - Attributes page allow you to specify grid attributes as well as the way in which the progress of coverage computations display.

  1. Select the 2D Graphics - Attributes page.
  2. Select the Show Regions check box in the Grid panel.
  3. Click Apply to apply the changes and keep the Properties Browser open.

Getting a better look

The sections and lines outlined on the globe represent coverage regions and individual points within those regions. The points have a specific geographical location and are used in the computation of assets available. Accessibility to a region is computed based on accessibility to the points within that region.

  1. Bring the 3D Graphics window to the front.
  2. Move around in the 3D Graphics window to get a good look at the coverage grid.

    3. 3D View: Stereo_Cov's grid display

  3. Move around in the 3D Graphics window to get a good look at the north and / or south pole.

    4. 3D View: Stereo_Cov's grid extents

    Notice that there is no grid covering either of these areas. When you limited the boundaries of your coverage region, the STK application excluded these areas from the grid.

Managing your resources

By default, the STK application is set to automatically recompute access every time an object on which the coverage definition depends (such as an asset) is updated. You will be computing access to a large area, which could take some time. In an effort to manage your resources more efficiently, turn off recomputing access automatically every time you make a change.

  1. Return to Stereo_Cov's () Properties ().
  2. Select the Basic - Advanced page.
  3. Clear the Automatically Recompute Accesses check box.
  4. Click OK to accept your changes and to close the Properties Browser.

Constraining your coverage

Your first objective is to determine what areas of the Earth, at some time in a 24 hour period, will be examined by at least one of the sensors during daylight hours. If coverage is based on access to every point in the grid, how will you ensure that the grid points are constrained based on the lighting conditions in that geographical area?

Once you have defined the grid area and resolution, you can customize the definition of points within the grid, by specifying a type of object or a specific object as a template for the points within the grid. The template object can be used to associate three types of information with the grid points: access constraints, basic object properties and, in some specialized cases, the altitude of the points in the grid. By default, the grid points are located on the surface of the Earth and accesses to grid points are constrained to a line-of-sight not obstructed by the Earth. If you select a template object, the constraints set for the template object are also used by all the points within the grid.

Creating the constraints template

Since you want to constrain your analysis based on the lighting conditions on the ground, apply a Lighting constraint to a new Facility object , then use the Facility object for your template.

  1. Bring the Insert STK Objects tool () to the front.
  2. Insert a facility () object using the Insert Default () method.
  3. Rename Facility1 () Const_Template.

Applying a Sun constraint

Any constraints or characteristics that you want to impose on points in the coverage grid must be applied to the template object. You can set a lighting constraint on Const_Template, which, once associated with the coverage definition, will be used by every point in the coverage grid.

  1. Open Const_Template's () Properties ().
  2. Select the Constraints - Active page.
  3. Click Add new constraints () in the Active Constraints toolbar.
  4. Select Lighting in the Constraint Name list when the Select Constraints to Add dialog box opens.
  5. Click Add.
  6. Click Close to close the Select Constraints to Add dialog box.
  7. Look at the Lighting panel in the Constraint Properties panel.

    8. The default selection is Direct Sun (total sunlight). This is the constraint you need for your analysis.

  8. Click OK.
  9. Clear the Const_Template () check box in the Object Browser.

The location and display of the constraints template is unimportant. You don't need to see the Facility object in either the 2D or 3D Graphics windows for it to be used analytically, so clearing it help keeps your scenario organized.

Associating the Sun constraint to the coverage grid

You have applied the appropriate constraint to the Const_Template Facility object, but you still need to associate that object with Stereo_Cov.

  1. Open Stereo_Cov's () Properties ().
  2. Select the Basic - Grid page when the Properties Browser opens.
  3. Click Grid Constraint Options... in the Grid Definition panel.
  4. Set the following options in the Grid Constraint Options dialog box:
    5. Option Value
    Reference Constraint Class Facility
    Use Object Instance Selected
  5. Select Const_Template in the Object Instance list.
  6. Click OK to close the Grid Constraint Options dialog box.
  7. Click Apply.

Identifying your coverage assets

You've defined and constrained the area within which you'd like to analyze coverage. The next step is to identify your assets. Coverage assets specify which objects, or assets in the scenario, will be used to provide coverage over the specified region.

The Earth-observing payload attached to each satellite (Shuttle, SunSync,and TestSat) are modeled using a Sensor object in this scenario; therefore, the sensors attached to each satellite will be your assets

  1. Select the Basic - Assets page.
  2. Expand () each Satellite object ().
  3. Hold down the Ctrl key and multi-select all three Sensor () objects.
  4. Click Assign.

    5. The display in the Assets list will change to visually indicate which objects in the scenario have been assigned as assets.

    Assigned assets for Stereo Cov

  5. Click OK.

Using the Compute Accesses tool

The ultimate goal of coverage is to analyze accesses to an area by using assigned assets and applying necessary limitations upon those accesses. You have a coverage definition (Stereo_Cov), which covers the surface of the Earth between 60 degrees and -60 degrees and you've assigned assets (the Earth-observing payload on each satellite) that will provide access to that area-of-interest. Now that the coverage definition object is defined and properly contained, access periods to the coverage area can be computed to determine the availability of an asset or set of assets that satisfy all geometric, lighting, temporal and other specified constraints. Use the Compute Accesses tool to compute accesses for the coverage definition.

  1. Bring the 2D Graphics window to the front.
  2. Right-click on Stereo_Cov () in the Object Browser.
  3. Select CoverageDefinition in the shortcut menu.
  4. Select Compute Accesses in the CoverageDefinition submenu.

    5. Coverage graphics display in the 2D Graphics window while coverage is being computed. When you compute coverage, all access calculations between the coverage assets (all three Sensor objects) and the coverage area (Stereo_Cov) are computed. A Progress Bar will display in the STK application's Status Bar which displays the Coverage computational progress (%).

    For larger-scale calculations, consider computing the accesses for coverage in parallel using multiprocessing. This can be done using multiple cores with Compute Accesses in Parallel. When you choose this option, the STK application saves the current state of your scenario to a temporary VDF; worker processes are started on the local machine or on the cluster machine depending on your configuration and then the results are sent back to the STK application.

    If you select white as the color for the coverage definition, you will not see any computational progress.

    2D View: Coverage computation display

Defining the quality of coverage with a simple coverage Figure of Merit

While the Coverage Definition object defines the problem, a Figure of Merit object allows you to evaluate the quality of coverage provided by the selected set of assets (defined for the Coverage Definition object) over the coverage area and then provide a method for summarizing and viewing the resultant data.

To evaluate coverage quality, you will first need to set basic parameters that determine the way in which quality is computed. This involves choosing the method for evaluating the quality of coverage provided, setting measurement options, and identifying the criteria needed to achieve satisfactory coverage.

Measuring simple coverage

Simple coverage measures whether or not a point is accessible by any of the assigned assets. An evaluation of the dynamic behavior of simple coverage computes a binary value of one (1) for points that are currently in an access period and zero (0) for points that are not. The static behavior of simple coverage similarly computes a binary value of one (1) for grid points that have access to an asset at any point in the analysis time period and zero (0) for points that are not accessible.

Evaluate the quality of coverage within your coverage region using a simple coverage type Figure of Merit object.

  1. Insert a Figure of Merit () object using the Insert Default () method.
  2. Select Stereo_Cov () in the Select Object dialog box.
  3. Click OK.
  4. Rename FigureOfMerit1 () Simple_Cov.

The STK application creates a simple coverage figure of merit by default. Since you will be evaluating simple coverage, there is no need to change SimpleCov's properties.

Configuring static coverage graphics

Graphics are used to represent the static and dynamic value of simple coverage. When displaying static graphics, grid points are highlighted if they are covered by at least one asset at any time during the analysis time period. The figure of merit display shows you where, during daylight hours, you have coverage by at least one asset during the coverage interval.

  1. Bring the 3D Graphics window to the front.
  2. Move around the 3D Graphics window to view the coverage quality.

3D View: Simple coverage quality for Stereo_Cov

In this case, the entire coverage region is shaded here in green. Your color could be different. This tells you that, at some point during the 24 hour analysis interval, each point in your coverage region did have access to at least one asset during daylight hours.

Viewing dynamic coverage graphics

Look at coverage graphics in the 2D Graphics window. In the 2D Graphics window you can see the entire globe as a flat map, whereas in the 3D Graphics window, the sunlit portion of the globe may be hidden when accesses occur.

  1. Bring the 2D Graphics window to the front.
  2. Click Decrease Time Step () in the Animation toolbar and set the Time Step to 10.00 sec.
  3. Click Start () to animate your scenario.

    4. 2D View: Simple coverage quality dynamic display

    The solar terminator as well as the subsolar point have already been enabled for you in the window's 2D Graphics Lighting properties so you can tell which portion of the Earth is in sunlight at any given time. Notice that throughout the 24 hour period not all of the satellites are in sunlit regions at the same time, and often only a portion of the field-of-view for a given satellite is in a sunlit region.

    Each of your assets has access for some portion of the 24 hour period, but how many of those assets have coverage in the same area simultaneously during daylight hours? A second Figure of Merit object can be used to answer that very question.

  4. Click Reset () when you are finished.

Cleaning up the 2D and 3D Graphics windows

In an effort to minimize clutter and more clearly visualize periods of access, remove the grid from the visualization windows and focus on the coverage quality display.

  1. Open Stereo_Cov's () Properties ().
  2. Select the 2D Graphics - Attributes page.
  3. Clear the Show Regions check box.
  4. Clear the Show Points check box.
  5. Click OK.
  6. Clear the check box beside Simple_Cov () in the Object Browser.

Defining the quality of coverage with N Asset Coverage

Insert a second Figure of Merit () object that will analyze the quality of coverage based on the number of available assets, called an N Asset Coverage Figure of Merit. N Asset Coverage measures the number of assets available simultaneously during coverage, where N is between zero and the total number of assets defined in the coverage definition. The dynamic definition of N Asset Coverage computes the number of assets currently accessible to each grid point.

Inserting a new Figure of Merit object.

Add a new Figure of Merit object to Stereo_Cov.

  1. Insert a Figure of Merit () object using the Insert Default () method.
  2. Select Stereo_Cov () in the Select Object dialog box.
  3. Click OK.
  4. Rename FigureofMerit2 () NAsset_Cov.

Using N Asset Coverage

Set the coverage definition properties to utilize N Asset Coverage.

  1. Open NAsset_Cov's () Properties ().
  2. Select the Basic - Definition page when the Properties Browser opens.
  3. Set the following in the Definition panel:
    4. Option Value
    Type N Asset Coverage
    Compute Maximum

    Selecting maximum computes the maximum number of assets available over the entire coverage interval. In this case, for every grid point the static value of the FOM is the maximum number of sensors (assets) simultaneously providing coverage during the analysis interval.

  4. Click Apply.

Getting a better look

View the coverage graphics in the 2D Graphics window.

  1. Bring the 2D Graphics window to the front.
  2. Review the quality of coverage.

    3. 2D View: NAsset FOM coverage graphics

    Your colors might be different from the image. The graphics indicate that you have access over the entire coverage grid.

Choosing the satisfaction criterion

You can restrict NAsset_Cov's behavior so that the STK application only applies the graphical properties when a chosen satisfaction criterion is met. Along with the Satisfaction criterion, you can change the Threshold at which satisfaction is achieved. The Threshold value depends on the type of Figure Of Merit you select. Change the criterion and threshold that will indicate which accesses are considered valid.

  1. Return to NAsset_Cov's () Properties ().
  2. Set the following in the Satisfaction panel:
    3. Option Value
    Enable Selected
    Satisfied If At Least
    Threshold 2

    The application of the Satisfaction criterion determines which grid points are graphically highlighted in the dynamic and static graphics. In this case, you want the Satisfaction Criterion to be that at least two (the selected threshold) of the assets (sensors) have access to a point in the grid simultaneously during daylight hours.

  3. Click Apply.

Decreasing the translucency

To ensure the graphics display brightly against the globe, you can decrease the percent translucency on the Figure of Merit's 2D Graphics - Static page.

  1. Select the 2D Graphics - Animation page.
  2. Enter 20 in the % Translucency field in the Show Points As panel.
  3. Click Apply.
  4. Select the 2D Graphics - Static page.
  5. Enter 20 in the % Translucency field in the Show Points As panel.
  6. Click OK.

Getting a better look

Adding the satisfaction criteria has greatly reduced your area of coverage as evidenced by the 2D and 3D Graphics display.

  1. Bring the 3D Graphics window to the front.

    2. 3D View: NAsset FOM satisfaction graphics

    Your colors might be different from the above image.

  2. Bring the 2D Graphics window to the front.
  3. Click Start () to animate your scenario.

    4. 2D View: NAsset FOM satisfaction graphics

    Notice that, as the scenario animates, a single sunlit sensor no longer shows dynamic coverage graphics. With the satisfaction criteria applied, you only see dynamic coverage graphics if there is double or triple coverage.

  4. Click Reset () when you are finished.

Graphing coverage by latitude

Create a Coverage By Latitude graph to confirm what you are seeing in the 2D Graphics window.

  1. Right-click on Stereo_Cov () in the Object Browser.
  2. Select Report & Graph Manager... () in the shortcut menu.
  3. Clear the Show Reports check box in the Styles list of the Report & Graph Manager.
  4. Select the Coverage By Latitude () graph in the Installed Styles () folder.
  5. Click Generate....

Understanding the coverage by latitude data provider

The coverage by latitude data provider reports coverage for each latitude in the selected range (-60 degrees to 60 degrees), at intervals depending on the selected resolution. A point is considered to be covered if it has access to one or more of the assigned assets. The reported values for each latitude are the average value for all grid points at that latitude.

  1. Review the Coverage by Latitude graph.

    2. Graph: Stereo Cov percent of time covered by latitude

    The graph coincides with what you see in the 2D and 3D Graphics windows. As your latitude increases, your coverage decreases.

  2. Close the Coverage by Latitude graph.
  3. Click Close to close the Report & Graph Manager.

Visualizing accumulated coverage

Your analysis up to this point has illustrated instantaneous coverage. You would also like to determine what areas, at some time during the day, had single, double, or triple coverage.

Setting the accumulation options

The accumulation options for animation graphics allow you to control the sense and persistence of the animation graphics. By default, the STK application is set to highlight grid points that meet the satisfaction criteria at the current time. When you change the accumulation value to Up to current time, grid points that have met the satisfaction criterion based on the dynamic definition of the figure of merit from the start time to the current time are highlighted during animation. This can help you determine not only where you have the best coverage but also when you have the best coverage.

  1. Open NAsset_Cov's () Properties ()
  2. Select the 2D Graphics - Animation page when the Properties Browser opens.
  3. Open the Show drop-down list in the Accumulation panel.
  4. Select Up to current time.
  5. Click Apply.

Viewing up to current time in the 2D Graphics window

Because you made minimal changes to the 2D Graphics properties for the NAsset_Cov (), by default both static and animation graphics display in the 2D and 3D Graphics windows. Whenever an assigned asset passes through the coverage area it leaves a footprint that indicates where the quality criteria (at least two assets) was met at a specific point in time.

  1. Bring the 2D Graphics window to the front.
  2. Click Start () to animate your scenario.

    3. 2D View: NAsset FOM up to current coverage

    In the above image, the pink shading (the static graphics) shows the sum of what has been covered by at least two assets at some time during the entire coverage interval. The yellow shading (animation graphics) shows how coverage is accumulated. When you animate the scenario, the animation graphics will accumulate as additional areas of the Earth are covered by at least two assets over time until they match the total static coverage for the coverage interval. Since the static coverage is the sum of the accumulated coverage it will eventually equal or add up to the static graphics.

  3. Click Reset () when you are finished.

Understanding contour graphics

You can specify how levels of coverage quality display in both the 2D and 3D Graphics windows using contour graphics. Contour levels represent the gradations in coverage quality and can be displayed for both static and animation values of the figure of merit.

Before you display contour graphics, turn off the display of the Animation graphics for NAsset_Cov.

  1. Return to NAsset_Cov's () Properties ().
  2. Select the 2D Graphics - Animation page.
  3. Clear the Show Animation Graphics check box.
  4. Click Apply.

Creating static contours

Static Contour levels display coverage data for all points based on evaluation over the entire coverage interval (in this case the analysis period).

  1. Select the 2D Graphics - Static page.
  2. Select the Show Contours option in the Display Metric panel.
  3. Click Remove All in Level Attributes panel.
  4. Enter the following values in the Level Adding panel:
    5. Option Value
    Add Method Start, Stop, Step
    Start 1
    Stop 3
    Step 1
  5. Click Add Levels.

Selecting the contour colors

Use a color ramp from red to blue for your coverage graphics. The Color Ramp method applies a spectrum pattern with selected start and end colors.

  1. Enter the following values in the Level Attributes panel:
    2. Option Value
    Color Method Color Ramp
    Start Color Red
    End Color Blue

    Note that the Start Color corresponds to the first Level value under Level Attributes.

  2. Click Apply.

Creating an embedded legend for the 2D and 3D Graphics windows

A contour key, or legend, provides you with a convenient way to interpret contour data displayed in the 2D and 3D Graphics windows. The Contours Legend window displays the coverage levels assigned along with the colors assigned to each level. The Contours Legend tool provides this information in a conveniently sized, easy-to-read window that can be kept on the side or in an unused corner of the screen throughout your Coverage session and, if desired, included in the display in your 2D and 3D Graphics windows. Add a legend to your 2D and 3D Graphics windows.

  1. Click Legend... in the Level Attributes panel.
  2. Click Layout... in the Static Legend for NAsset_Cov floating legend.

    3. The Contours Legend Layout window allows you to adjust the position of the legend display in the 2D and 3D Graphics windows, the width of the color bands and the order in which the coverage levels are presented (maximum to minimum or vice versa).

  3. Select the Show at Pixel Location check box in both the 2D Graphics Window and 3D Graphics Window panels in the Figure of Merit Legend Layout dialog box.
  4. Click OK to close the Figure of Merit Legend Layout dialog box.
  5. Close the Static Legend for NAsset_Cov floating legend window.

Viewing the legend

View the legend you just added to the 2D and 3D Graphics windows.

  1. Bring either the 2D or 3D Graphics window to the front.
  2. You should see the legend in either window.

    3. Static contours legend for NAsset coverage

    The map graphics will be colored according to the number of available assets as outlined in the static contours legend.

Selecting natural neighbor sampling

You would like a smoother effect for the contours in your 2D and 3D Graphics windows. You can to use the Natural Neighbor Sampling option to accomplish this.

  1. Return to NAsset_Cov's () Properties ().
  2. Select the 2D Graphics - Static page.
  3. Select the Natural Neighbor option in the Contour Interpolation (points must be filled) panel.

    4. This option is not valid for these Coverage Definition types: Latitude Line, Longitude Line, and Custom Boundary.

  4. Click Apply.

Getting a better look

Color is applied smoothly over all points in the grid to differentiate contour levels. If you choose the Natural Neighbor Sampling, the value of the Figure of Merit is determined for each screen pixel within the coverage area using a natural neighbor interpolation algorithm based on the computed values of the Figure of Merit at the grid points. In the case of discreet figures of merit, interpolated values are rounded to the nearest integer. View the changes in both the 2D and 3D Graphics windows.

  1. Bring the 2D Graphics window to the front.
  2. Review the contours.

    3. 2D View: NAsset FOM static contours display

  3. Bring the 3D Graphics window to the front.
  4. Review the contours.

    5. 3D View: NAsset FOM static contours display

Creating dynamic contours

The static contour display tells you where you have access to at least one (red), two (green), or three (blue) assets at some point during the entire coverage interval. Take contours a step further. Display contours that will tell you how many assets you have access to based on the scenario time.

  1. Return to NAsset_Cov's () Properties ()
  2. Select the 2D Graphics - Static page.
  3. Clear the Show Static Graphics check box.
  4. Select the 2D Graphics - Animation page.
  5. Select the Show Animation Graphics check box.
  6. Select the Show Contours option in the Display Metric panel.
  7. Click Copy Static Levels in the Level Attributes panel.
  8. Click Yes to confirm.

    9. Selecting Copy Static Levels ensures that the same contour levels and colors are used for both static and animation graphics.

  9. Select the Natural Neighbor option in the Contour Interpolation (points must be filled) panel.
  10. Click OK.

Getting a better look

As your scenario animates areas in the coverage grid that have access to all three assets will be blue, the areas with double coverage will be green, and those with single coverage will be red.

  1. Bring the 2D Graphics window to the front.
  2. Click Start () to animate your scenario.

    3. 2D View: NAsset dynamic contours display

  3. Click Reset () when you are finished.

Contour graphics have shown you that you have coverage from one and two assets at various times throughout your coverage analysis, but how long do you have that coverage, and exactly where? You can use yet another type of Figure of Merit object to help answer that very question.

Removing NAsset_Cov's graphics

Before you create another Figure of Merit object, turn NAsset_Cov's graphics off, so that they don't interfere with the coverage quality display of the new Figure of Merit object.

  1. Clear the check box next to NAsset_Cov () in the Object Browser.

Using a Coverage Time Figure of Merit object

A Coverage Time Figure of Merit measures the amount of time during which grid points are covered. Because Coverage Time does not have a dynamic definition, no time-dependent information is computed.

Inserting a third Figure of Merit object

Add a new Figure of Merit object to gauge Coverage Time.

  1. Insert a Figure of Merit () object using the Insert Default () method.
  2. Select Stereo_Cov () in the Select Object dialog box.
  3. Click OK.
  4. Rename FigureOfMerit3 () Cov_Time.

Measuring coverage time

Set the Figure of Merit type to Coverage Time.

  1. Open Cov_Time's () Properties ().
  2. Select the Basic - Definition page when the Properties Browser opens.
  3. Set the following in the Definition panel.
    4. Option Value
    Type Coverage Time
    Compute Total Time Above
    Min # Assets 2

    The Total Time Above option computes the amount of time (over the entire coverage interval) during which a point is covered by at least the minimum number of assets specified.

  4. Click Apply.

Decreasing the translucency

To ensure the graphics display brightly against the globe, you need to decrease the percent translucency.

  1. Select the 2D Graphics - Static page.
  2. Enter 20 in the % Translucency field in the Show Points As panel.
  3. Click Apply.

Getting a better look

View the coverage time graphics in the 2D Graphics window.

  1. Bring the 2D Graphics window to the front.
  2. Move around to see how the coverage over the globe.

    3. 2D View: Cov Time FOM graphics display

    Your colors could be different from the above image. The shaded points on the 2D Graphics window are those that have some amount of time when they are covered by two assets simultaneously.

Reporting coverage time

Cov_Time's display shows that you have at least two assets viewing parts of the southern latitudes over the entire coverage interval. But what are the maximum, minimum, and average values over the entire coverage region? Use a Grid Stats report to summarize the minimum, maximum and average static value for Cov_Time over the entire grid. The values in the Grid Stats report are a great way to determine the start and stop values to specify when enabling contour graphics.

  1. Right-click on Cov_Time () in the Object Browser.
  2. Select Report & Graph Manager... () in the shortcut menu.
  3. Select the Show Reports check box in the Styles panel in the Report & Graph Manager.
  4. Clear the Show Graphs check box.
  5. Select the Grid Stats () report in the Installed Styles () folder .
  6. Click Generate....
  7. Note the minimum (e.g. 0.000 seconds), maximum (e.g. ~1697 seconds) and average (e.g. ~70 seconds) values for Cov_Time to help you define your contour levels.
  8. Close the report and the Report & Graph Manager.

Creating coverage time contours

Now that you have the values for your coverage time, you can use them to set the intervals for Cov_Time's contour graphics.

  1. Return to Cov_Time's () Properties ().
  2. Select the 2D Graphics - Static page.
  3. Select the Show Contours option in the Display Metric panel.
  4. Click Remove All in the Level Attributes panel.
  5. Set the following values in the Level Adding panel:
    6. Option Value
    Add Method Start, Stop, Step
    Start 100 sec
    Stop Round down to nearest 100 below the Maximum (sec) value found in the Grid Stats report (e.g. 1600 sec)
    Step 250 sec

    Any times under 100 seconds will show no color in both the 2D and 3D Graphics windows. Any times above 1600 seconds will show the end color.

  6. Click Add Levels.

Selecting the contour colors

Adjust the color ramp options for your contours.

  1. Enter the following values in the Level Attributes panel:
    2. Option Value
    Color Method Color Ramp
    Start Color Red
    End Color Blue
  2. Select the Natural Neighbor option in the Color Interpolation (points must be filled) panel.
  3. Click Apply.

Creating an embedded legend for the 2D and 3D Graphics windows

As before, add a legend to your 2D and 3D Graphics windows.

  1. Click Legend... in the Level Attributes panel.
  2. Click Layout... in the Static Legend for Cov_Time floating legend.
  3. Select the Show at Pixel Location check box in both the 2D Graphics Window and 3D Graphics Window panels in the Figure of Merit Legend Layout dialog box.
  4. Enter Coverage Time (seconds) in the Title field in the Text Options panel.
  5. Enter 0 in the Number Of Decimal Digits field.
  6. Enter the following values in the Range Color Options panel:
    7. Option Value
    Max Color Squares per Row 40
    Color Squares Width (pixels) 50
    Color Square Height (pixels) 20
  7. Click OK to close the Figure of Merit Legend Layout dialog box.
  8. Close the Static Legend for Cov_Time floating legend.
  9. Click OK to close the Properties Browser.

Getting a better look

View your contours and legends in the 2D and 3D Graphics windows.

  1. Bring the 2D Graphics window to the front.

    2. 2D View: Cov Time FOM static contour display with legend

    The legend is now embedded in the 2D map display for easy reference. The map graphics will be colored according to the length of time that assets are available as outlined in the static contours legend.

  2. Bring the 3D Graphics window to the front.
  3. Move around to see how the contours cover the globe.

    4. 3D View: Cov Time FOM static contour display with legend

Reporting coverage time by grid point

The contours display provides a general overview of when you have coverage by two or more assets for how long, and the animation time can serve as a reference for when you the extended periods of coverage occur. To get a more thorough outline of the exact length of time each point in the grid is covered by two or more assets, create a report of values by grid point.

Creating a Value by Grid Point report

A Value by Grid Point report returns a detailed list which includes the geodetic coordinates of each point in the grid, and the length of time that each point is covered by at least two assets (the minimum assets specified in the FOM definition) while in direct sunlight (the constraint imposed on the grid points using the Const_Template facility object).

  1. Right-click on Cov_Time () in the Object Browser.
  2. Select Report & Graph Manager... () in the shortcut menu.
  3. Select the Value By Grid Point () report in the Installed Styles () list.
  4. Click Generate....
  5. Review the report.
    • Are there any grid points in the southern hemisphere that have values?
    • Which latitude / longitude has the highest value (most time covered)?
  6. When you finish, close the Value By Grid Point report.
  7. Click Close to exit the Report & Graph Manager.

Using the Grid Inspector tool

The Grid Inspector tool is an object-level tool that is available for Coverage Definition and Figure of Merit objects. For a Coverage Definition object, the Grid Inspector provides in-depth information about raw access data. For the Figure of Merit object, the Grid Inspector provides detailed quality-related information. Since you're interested in the amount of time that multiple satellites cover an area, you will use the Grid Inspector tool for the figure of merit to see the exact FOM values for each area.

Preparing the 2D Graphics window for the Grid Inspector tool

In order to use the Grid Inspector tool, you must show the grid points in the 2D Graphics window.

  1. Open Stereo_Cov's () Properties ().
  2. Select the 2D Graphics - Attributes page when the Properties Browser opens.
  3. Select the Show Regions check box in the Grid panel.
  4. Select the Show Points check box.
  5. Click OK.

Opening the Grid Inspector tool

Open the Grid Inspector tool for Cov_Time.

  1. Bring the 2D Graphics window to the front.
  2. Right-click on Cov_Time () in the Object Browser.
  3. Select FigureOfMerit in the shortcut menu.
  4. Select Grid Inspector... () in the FigureOfMerit submenu.

Obtaining region data

Inspect a region using the Grid Inspector tool.

  1. Open the Action drop-down list.
  2. Choose Select Region.
  3. Bring the 2D Graphics window to the front.
  4. Click anywhere in the 2D Graphics window where there is coverage.
  5. Read the information in the Messages field concerning the selected region.

Changing the Figure of Merit

There are several reports and graphs available for Coverage Definition objects through the Grid Inspector tool. The available report options depend on the object selected. Time-dependent data is not available for Cov_Time; however, it is for NAsset_Cov.

  1. Clear the Cov_Time () check box in the Object Browser.
  2. Select the NAsset_Cov () check box in the Object Browser.
  3. Open NAsset_Cov's () Properties ().
  4. Select the 2D Graphics - Animation page when the Properties Browser opens.
  5. Clear the Show Animation Graphics check box.
  6. Click Apply.
  7. Select the 2D Graphics - Static page.
  8. Select the Show Static Graphics check box.
  9. Click OK.

Creating a Region Figure of Merit report

The Region Coverage report or graph provides a summary of coverage for the region selected in the graphics window. The report includes a time-ordered breakdown of the percentage of the region covered, area of the region covered, percentage of accumulated coverage and accumulated area of coverage. The covered area is computed by summing the areas represented by covered points within the region.

  1. Bring the Grid Inspector tool to the front.
  2. Click Select Object....
  3. Select NAsset_Cov () in the Select Object dialog box.
  4. Click OK.
  5. Open the Action drop-down list.
  6. Choose Select Region.
  7. Click on a grid point anywhere in the 2D Graphics window where there is coverage.
  8. Click Region FOM ... in the Reports panel.
  9. Review the data in the report.
  10. Close the report when you are finished.

Narrowing the focus to just one point

Narrow the focus to an actual point.

  1. Open the Action drop-down list.
  2. Choose Select Point.
  3. Bring the 2D Graphics window to the front.
  4. Click on a grid point where there is coverage.
  5. Read the information in the Messages field concerning the selected point.
  6. Feel free to continue to click various points in the Coverage results.

    7. The Messages field displays, among other information, the value of the Total Time covered by 2 or more assets for that point.

  7. Feel free to create any report or graphs.
  8. Close the Grid Inspector tool when you are done.

Saving your work

Close out your work and save your scenario.

  1. Close any open reports, properties and the Report & Graph Manager.
  2. Save () your work.

Summary

You learned how to use a Coverage Definition object to include defining the grid, creating a direct sun constrained template object and applying that to the grid. You learned how to choose coverage assets. You looked at multiple Figures of Merit setups and analyzed simple , number of assets and coverage time coverage. You used multiple data providers to analyze your grid. Using the data, you created color contours that corresponded to the data. Finally, you used the Grid Inspector tool to focus analysis in selected regions and points inside of the coverage grid.