Getting Started with Coverage

STK Pro, STK Premium (Air), STK Premium (Space), or STK Enterprise
You can obtain the necessary licenses for this training 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.

Capabilities Covered

This lesson covers the following STK Capabilities:

  • STK Pro
  • Coverage

Problem Statement

As a university student, your senior design team has worked in conjunction with a consortium of two other universities in designing a new space-based Earth observing payload. Your payload was designed to be an on-orbit space shuttle experiment rather than a stand-alone satellite. The space shuttle has just lifted off with your payload on-board! The other two universities built small satellites carrying this new payload (SunSync and TestSat). Their satellites launched previously on two separate space launches. Because the three Earth observing payloads were all piggy-backed to space as secondary missions of other launches, they ended up in three different orbits.

You need to know when any or all of the three satellites can “see” the portion of the Earth’s surface that falls between 60 degree and -60 degrees latitude. Additionally, you would like to know if any areas of the Earth will be covered by two or even three sensors simultaneously, during daylight hours, and if so, for how long.

Manually calculating point-to-point access to an object positioned at every point on the Earth individually would be time consuming. How will you determine the extent and quality of coverage provided by the three satellites that you are assessing?

Break It Down

You have some information that may be helpful. Here’s what you know:

  1. The Earth observing payload is attached to three different satellites (Shuttle, SunSync, and TestSat).
  2. The shuttle is flying in a low earth orbit with a 51.6 degree inclination.
  3. One of the university satellites is in a sun synchronous orbit (SunSync).
  4. The other satellite is in a circular orbit with an altitude of 1400 km and an inclination of 70 degrees (TestSat).
  5. The Earth observing mission that these satellites are performing requires the Earth to be in sunlight in order for data collection to occur.
  6. 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.

Solution

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

Video Guidance

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

Model the world!

The first thing you need to do is create a scenario.

  1. Open STK and click the Open a Scenario () button.
  2. Browse to <STK Install Folder>\Data\Resources\stktraining\VDFs and select Coverage_GettingStarted.vdf.

    3. If using an older version of STK, browse to <STK install folder>\Data\Resources\stktraining\samples and open SimSatCov.vdf.

  3. Click Open .

    4. When you open the scenario, a directory with the same name as the scenario will be created in the default user directory (C:\Users\<username>\Documents\STK 12\. The scenario will not be saved automatically.

    When you save a scenario in STK, it will save in the format in which it originated. In other words, if you open a VDF, the default save format will be a VDF. The same is true for a scenario file (*.sc). If you want to save a VDF as a SC file (or vice-versa), you must change the file format when you are performing the Save As procedure.

  4. Click File on the menu bar.
  5. Select Save As...
  6. Navigate to your student area (C:\Users\<username>\Documents\STK 12\).
  7. Create a folder called Coverage_GettingStarted.
  8. Ensure the file type is a Scenario file (*.sc).
  9. Save the scenario as Coverage_GettingStarted.

What's In My Scenario?

The scenario provided 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.

3D View: Three predefined orbits

What is Coverage?

Coverage allows you to analyze the global or regional coverage provided by one or more assets (facilities, vehicles, sensors, etc.) while considering all access. Specific results are generated based on detailed access computations performed to user-defined grid points within an area of coverage. Using Coverage you can:

  • Define areas of interest
  • Define coverage assets (satellites, ground facilities, etc.)
  • Define the time period of interest
  • Determine and report measures of coverage quality

Coverage provides the necessary tools, but you have some work to do too. Let’s get started.

Coverage Definition

You know what your region-of-interest is--the portion of the Earth’s surface that falls between 60 degree and -60 degrees latitude. You need to tell STK to use that area as your region-of-interest. Use a coverage definition object to define an analytical area that will limit itself to user defined boundaries. A coverage definition object is defined by:

  • Selecting the area(s) of interest
  • Identifying the assets that may provide coverage to those areas
  • Setting the time period over which coverage statistics are to be analyzed

Once the coverage definition object is defined, 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 user-specified constraints within that area.

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 STK. Points have specific geographical locations and are used in the computation of asset availability. Regions are closed boundaries that contain points. Accessibility to a region is computed based on accessibility to the points within that region. The combination of the geographical area, the regions within that area, and the points within each region is called the coverage grid.

The default Grid Definition type is set to Latitude Bounds. This definition results in a coverage region that is a band circling the globe between your defined latitude boundaries.

  1. Insert a Coverage Definition () using the Insert Default method.
  2. Rename the Coverage Definition Stereo_Cov.
  3. Open Stereo_Cov's () Properties (). The Basic - Grid page should already be selected.
  4. In the Grid Area of Interest section, set the following:
    5. Option Value
    Type Latitude Bounds
    Min Latitude -60 deg
    Max Latitude 60 deg

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 is based on a set of locations, or points, which span the coverage area. You can determine the spacing between grid points using the options in the Point Granularity area 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 resolution typically produces more accurate results but requires additional computational time and resources.

  1. Ensure that Lat/Lon is selected in the Grid Definition - Point Granularity section
  2. Change the Point Granularity to 4 deg.
  3. Click Apply to apply the changes and keep the Properties Browser open.

Coverage Graphics

You can define how the coverage grid displays 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.

Let’s turn on the 2D and 3D grid region display now.

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

Get 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. Mouse around in the 3D Graphics window to get a good look at the coverage grid.

    3. 3D View: Stereo Cov's grid display

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

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

    3D View: Stereo Cov's grid extents

Manage Your Resources

By default, STK 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. You still have several changes to make. In an effort to manage your resources more efficiently, let’s not tie up STK recomputing access automatically every time you make a change. Let’s turn that off.

  1. Return to Stereo_Cov's () properties ().
  2. Select the Basic - Advanced page.
  3. Clear the Automatically Recompute Accesses check box.
  4. Click OK .

How Will I Constrain My Coverage?

Your first objective is to determine what areas of the Earth, at some time in a twenty-four 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 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.

Create the Constraints Template

Since you want to constrain your analysis based on the lighting conditions on the ground, apply the constraints to a facility object and then use that facility as your template.

  1. Insert a facility () object using the Insert Default method.
  2. Rename the facility Const_Template.

Apply Constraints

Any constraints or characteristics that you want to impose on points in the coverage grid must be applied to a 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 - Sun page.
  3. Select the Lighting check box.
  4. Select Direct Sun from the list of lighting constraints.
  5. Click Apply to apply the changes and keep the Properties Browser open.

    6. The location and display of the constraints template is unimportant. Take a moment to turn off the object label in the 2D and 3D Graphics windows.

  6. Select the 2D Graphics - Attributes page.
  7. Set the following:
    8. Option Value
    Marker Style None
    Inherit From Scenario Off
    Show Label Off
  8. Select the 3D Graphics - Model page.
  9. Set the following options:
    10. Option Value
    Model - Show Off
    Marker - Show Off
  10. Click OK .

Associate the Constraints

You’ve applied the appropriate constraint to the template object (Const_Template), but you still need to associate that object with the Coverage Definition (Stereo_Cov).

  1. Open Stereo_Cov's () properties ().
  2. Ensure that the Basic - Grid page is selected.
  3. Click Grid Constraint Options... .
  4. Set the following:
    5. Option Value
    Reference Constraint Class Facility
    Use Object Instance On
    <Object Instance> Const_Template (highlight)
  5. Click OK to return to the Grid page.
  6. Click Apply to apply the changes and keep the Properties Browser open.

Identify Your 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 payloads attached to each satellite (Shuttle, SunSync,and TestSat) are modeled using an STK sensor object in this scenario; therefore, the sensors attached to each satellite will be your assets. Let’s assign those assets now.

  1. Select the Basic - Assets page.
  2. Expand () each satellite object () to unnest the attached payloads.
  3. Hold down the Ctrl key and select all three sensors ().
  4. Click the Assign button.

    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 .

Compute Coverage!

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. Let’s do that now.

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

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 sensors) and the coverage area (Stereo_Cov) are computed. A Progress Bar will display in STK'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 on a local machine, or taking advantage of cluster configurations, depending upon your machine configuration. For more information on machine configuration, installation of the Parallel Extension, licensing, and more, please see the STK Help system.

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

2D View: Coverage computation display

Define the Quality of Coverage

While the coverage definition defines the problem, the figure(s) of merit 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.

Measure 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 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 computes a 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.

Let’s evaluate the quality of coverage within your coverage region using a simple coverage type figure of merit (FOM).

  1. Insert a Figure of Merit () using the Insert Default method.

  2. You may need to add the Figure or Merit object to the Insert STK Objects tool. To do this, click the Edit Preferences... button and select it from the New Object page.

  3. Select Stereo_Cov () in the Select Object pop up.
  4. Click OK .
  5. Rename the figure of merit Simple_Cov.

STK creates a Simple Coverage figure of merit by default. Since you will be evaluating simple coverage there is no need to change Simple Cov’s properties.

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. Reset () the animation.

    3. 3D View: Simple coverage quality for Stereo Cov

    In this case, the entire coverage region is shaded here in red. This tells you that, at some point during the twenty-four analysis interval, each point in your coverage region did have access to at least one asset during daylight hours.

Dynamic Coverage Graphics

Let’s look at coverage graphics in the 2D Graphics window. In the 2D Graphics window we 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. Play () the animation.

    3. 2D View: Simple coverage quality dynamic display

By default the solar terminator as well as the subsolar point have already been enabled for you so you can tell which portion of the Earth is in sunlight at any given time. Notice that throughout the twenty-four 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.

It’s obvious that each of your assets has access for some portion of the twenty-four hour period, but how many of those assets have coverage in the same area simultaneously during daylight hours? A second FOM can be used to answer that very question.

Clean Up!

In an effort to minimize clutter and more clearly visualize periods of access, let’s 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. In the Object Browser, clear the check box beside Simple_Cov () to toggle its graphics display off.

N Asset Coverage

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.

Let’s add a second FOM object that will analyze the quality of coverage based on the number of available assets.

Definition

  1. Insert a Figure of Merit () object using the Define Properties method.
  2. Select Stereo_Cov () in the Select Object pop up.
  3. Click OK .
  4. Rename the figure of merit NAsset_Cov.
  5. Select the Basic - Definition page.
  6. Set the following Definition criteria:
    7. Option Value
    Type N Asset Coverage
    Compute Maximum

    Selecting maximum will compute 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.

  7. Click Apply to apply the changes and keep the Properties Browser open.

Get a Better Look

  1. Bring the 2D Graphics window to the front.
  2. Reset () the animation to refresh the display in the 2D Graphics window.

    3. 2D View: NAsset FOM coverage graphics

    The graphics indicate that you have access over the entire coverage grid. Let’s change the criteria that will indicate which accesses are considered valid.

Satisfaction

You can restrict the figure of merit behavior so that STK only applies the graphical properties of the figure of merit when a chosen satisfaction criterion is met.

  1. Return to NAsset_Cov’s () properties ().
  2. Set the following Satisfaction section criteria:
    3. Option Value
    Enable On
    Satisfied If At Least
    Threshold 2

    In this case, you want the satisfaction criteria 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 to apply the changes and keep the Properties Browser open.

Decrease the Translucency

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

  1. Select the 2D Graphics - Animation page.
  2. Set the % Translucency to 10 percent.
  3. Click Apply .
  4. Select the 2D Graphics - Static page.
  5. Set the % Translucency to 10 percent.
  6. Click OK .

Get a Better Look

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

  1. Reset () the animation.
  2. Bring the 3D Graphics window to the front.

    3. 3D View: NAsset FOM satisfaction graphics

  3. Bring the 2D Graphics window to the front.
  4. Play () the animation.

    5. 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.

Graph Coverage by Latitude

Let’s create a graph to confirm what you are seeing in the 2D Graphics window.

  1. Open the Report & Graph Manager ().
  2. Select the following:
    3. Option Value
    Object Type Coverage Definition
    Object (Below Object Type) Stereo_Cov
    Show Reports Off
    Show Graphs On
    Style Coverage by Latitude
    Generate as Report/Graph
  3. Click Generate... .

Coverage By Latitude Data Provider

The Coverage by Latitude data provider reports coverage for each latitude in the selected range (-90 degrees to 90 degrees if Global Coverage is chosen), 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.

Graph: Stereo Cov percent of time covered by latitude

The graph clearly coincides with what you see on the map. As your latitude increases, your coverage decreases.

Use the graph to answer the following questions:

  • Where would be the best to place to put a ground station for data collection?
  • Would you have access to multiple assets at the same time?
  1. Close the Coverage by Latitude graph.
  2. Close the Report & Graph Manager ().

Multiple Asset Coverage

You have determined that the southern latitudes provide the best coverage, and it would, therefore, be beneficial to put a data collection ground station somewhere in a southern latitude. Your analysis, up to this point, has illustrated our instantaneous coverage, but, you would also like to determine what areas, at some time during the day, had single, double, or triple coverage.

  1. Open NAsset_Cov’s () properties ()
  2. Select the 2D Graphics - Animation page.
  3. In the Accumulation - Show field, select Up to Current Time.
  4. Click Apply to apply the changes and keep the Properties Browser open.

The accumulation options for animation graphics allow you to control the sense and persistence of the animation graphics. By default, STK 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, 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.

Get a Better Look

Because we have made minimal changes to the 2D Graphics properties for the NAsset_Cov FOM, by default both static and animation graphics display in the visualization 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.

In the figure below, 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. If 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.

  1. Bring the 2D Graphics window to the front.
  2. Reset () the animation.
  3. Play () the animation.

    4. 2D View: NAsset FOM up to current coverage

Contour Graphics

You can specify how levels of coverage quality display in both the 2D and 3D Graphics windows using contours 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, let’s 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. Disable the Show Animation Graphics option.
  4. Click Apply to apply the changes and keep the Properties Browser open.

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. Set the following options:
    3. Option Value
    Show Static Graphics On
    Filled Area - % Translucency 15
  3. Enable the Show Contours option.
  4. Click the Remove All button in the Level Attributes page.
  5. Enter the following values in the Level Adding area:
    6. Option Value
    Add Method Start, Stop, Step
    Start 1
    Stop 3
    Step 1
  6. Click Add Levels .
  7. Enter the following values in the Level Attributes area:
    8. Option Value
    Color Method Color Ramp
    Start Color Red
    End Color Blue
  8. Click Apply to apply the changes and keep the Properties Browser open.
  9. Click the Legend... button.
  10. Click the Layout... button.
  11. Select the Show at Pixel Location check box in either the 2D Graphics Window or 3D Graphics Window section or both depending where you want the legend to display.
  12. Click OK and then close the floating legend layout window. You should see a legend in the chosen Graphics Window(s).

    13. 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.

Set the Natural Neighbor Sampling

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

  1. On the 2D Graphics - Static page, locate the Contour Interpolation section.
    2. Option Value
    Natural Neighbor On
    Sampling: Medium Sampling

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

  2. Click OK to apply the changes and dismiss the Properties Browser.

    3. 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.

Get a Better Look

  1. Reset () the animation to refresh the visualization windows.
  2. Bring the 2D Graphics window to the front.

    3. 2D View: NAsset FOM static contours display

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

    4. 3D View: NAsset FOM static contours display

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. Let’s take contours a step further. Let’s display contours that will tell you how many assets you have access to based on the scenario time.

  1. Open NAsset_Cov’s () properties ()
  2. Select the 2D Graphics - Static page.
  3. Clear the Show Static Graphics check box.
  4. Click Apply to apply the changes and keep the Properties Browser open.
  5. Select the 2D Graphics - Animation page.
  6. Set the following:
    7. Option Value
    Show Animation Graphics On
    Filled Area 15% Translucency
  7. Set the following:
    8. Option Value
    Show Contours On
    Natural Neighbor On
    Sampling: Medium Sampling

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

  8. Click Copy Static Levels to ensure the same levels you selected before are being computed now.
  9. Click Yes on the informational message that explains your contour levels will be overwritten.
  10. Click OK .

Get 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. Reset () the animation to refresh the visualization windows.
  2. Bring the 2D Graphics window to the front.
  3. Play () the animation.

    4. 2D View: NAsset dynamic contours display

    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 FOM to help answer that very question.

  4. When you finish, reset () the animation.

Clean Up

Before you create another FOM, turn the NAsset_Cov FOM graphics off, so that they don’t interfere with the coverage quality display of the new FOM.

Measure Coverage Time

Coverage Time 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.

  1. Insert a Figure of Merit () object using the Define Properties method.
  2. Select Stereo_Cov () in the Select Object pop up.
  3. Click OK .
  4. Rename the Figure of Merit Cov_Time.
  5. Select the Basic - Definition page.
  6. Set the following:
    7. 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.

  7. Click Apply to apply the changes and keep the Properties Browser open.

Decrease 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. Set the % Translucency to 10 percent.
  3. Click Apply to apply the changes and keep the Properties Browser open.

Get a Better Look

The shaded points on the 2D Graphics window are those that have some amount of time when they are covered by two assets simultaneously.

  1. Reset () the animation to refresh the visualization windows.
  2. Bring the 2D Graphics window to the front.

    3. 2D View: Cov Time FOM graphics display

Report Coverage Time

The FOM 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?

  1. Open the Report & Graph Manager ().
  2. Select the following:
    3. Option Value
    Object Type Figure of Merit
    Object (Below Object Type) Cov_Time
    Show Reports On
    Show Graphs Off
    Style Grid Stats
    Generate as Report/Graph
  3. Click Generate... .

    4. The Grid Stats report summarizes the minimum, maximum and average static value for the figure of merit 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 graphics contours.

    • What are the minimum, maximum, and average values for the figure of merit?
  4. Note these values to help you define your contour levels.
  5. Close the Report & Graph Manager (), but leave the Grid Stats report open.

Coverage Time Contours

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

  1. Return to Cov_Time’s () properties ().
  2. Select the 2D Graphics - Static page.
  3. Set the following display options:
    4. Option Value
    Show Static Graphics On
    Filled Area 15% Translucency
  4. Enable the Show Contours option.
  5. Click Remove All in the Level Attributes section.
  6. Set the following values in the Level Adding section:
    7. Option Value
    Add Method Start, Stop, Step
    Start 100 sec
    Stop The nearest 100 above the Maximum (sec) value found in the Grid Stats report
    Step 200 sec
  7. Click Add Levels .
  8. Enter the following values in the Level Attributes section:
    9. Option Value
    Color Method Color Ramp
    Start Color Red
    End Color Blue
  9. Set the following options in the Color Interpolation section.
    10. Option Value
    Natural Neighbor On
    Sampling: Medium Sampling
  10. Click Apply .

Change the Legend Layout

Let’s displays in the 2D Graphics window.

  1. Click the Legend... button.
  2. Click the Layout... button.
  3. Enter the following values in the Figure of Merit Legend Layout.
    4. Category Option Value
    2D Graphics Window Show at Pixel Location On
    Text Options Number of Decimal Digits 0
    Range Color Options

    Max Color Squares per Row

    Color Squares Width

    Color Square Height

    40

    50

    20
  4. Bring the 2D Graphics window to the front.
  5. With the Figure of Merit Legend Layout dialog open, click the location where you’d like to position the upper left corner of the legend in the 2D Graphics window.
  6. When you finish, click OK to dismiss the Figure of Merit Legend Layout dialog.
  7. Close the Legend Layout Window and the floating Legend window.
  8. Click OK on the properties page.
  9. Close the Grid Stats report.

Get a Better Look

  1. Bring the 2D Graphics window to the front.
  2. Reset () the animation.

    3. 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.

  3. Bring the 3D Graphics window to the front.
  4. Mouse around to see how the contours cover the globe.

    5. 3D View: Cov Time FOM static contour display with legend

Report 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, let’s create a report.

  1. Open the Report & Graph Manager ().
  2. Select the following:
    3. Option Value
    Object Type Figure of Merit
    Object (Below Object Type) Cov_Time
    Show Reports On
    Show Graphs Off
    Style Value By Grid Point
    Generate as Report/Graph
  3. Click Generate... .

    4. The Value by Grid Point data provider 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).

    • Are there any grid points in the southern hemisphere that have values?
    • Which latitude/longitude has the highest value (most time covered)?
  4. When you finish, close the Value By Grid Point report.
  5. Close the Report & Graph Manager ().

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, the Grid Inspector provides in-depth information about raw access data. For the figure of merit, 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.

  1. Right-click Cov_Time () in the Object Browser.
  2. Extend the FigureofMerit menu.
  3. Click Grid Inspector.
  4. Set the Action field to Select Region.
  5. Bring the 2D Graphics window to the front.
  6. Click anywhere in the 2D Graphics window where there is coverage.
    • Is there a point where three of your satellites cover an area?
    • Is there any region where you have 100% coverage?

Region FOM Report

  1. In the Object Browser, clear the check box beside Cov_Time () to toggle the graphics display off and select the box NAsset_Cov () to toggle the graphics display on.
  2. Right-click on NAsset_Cov () in the Object Browser and select Properties ().
  3. On the 2D Graphics - Animation page, clear the Show Animation Graphics check box.
  4. On the 2D Graphics - Static page, select the Show Static Graphics check box.
  5. Click OK .
  6. Bring the Grid Inspector tool to the front.
  7. Click the Select Object... button to change the Inspect FOM to NAsset_Cov.
  8. Set the Action field to Select Region.
  9. Click anywhere in the 2D Graphics window where there is coverage.
  10. Click Region FOM... in the Reports section.

Narrow the Focus to One Point

Let’s narrow the focus to an actual point.

  1. Set the Action option to Select Point.
  2. Bring the 2D Graphics window to the front.
  3. Click anywhere in the Coverage results area.
  4. Feel free to continue to click various points in the Coverage results.

    5. The information displays the Coverage Time at each specific point.

  5. Close the Grid Inspector when done.

When You Finish

  1. Save () your work.
  2. Close the scenario ().
  3. Leave STK () open.