Part 8: Compute Coverage Over Regions

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 lesson 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

Engineers and operators need to analyze both global and regional coverage from one or more assets. Coverage analyses may need to account for constraints, such as lighting conditions and terrain, or simply determine whether a sensor footprint passes over a specific ground location. They may even need to analyze a large area of ground or space to examine communication link bit error rates in terms of the area of interest, age of the data, dilution of precision, and so on. You want to analyze the extent of coverage provided by three Earth-observing satellite sensor payloads located in different orbits. You need to determine what percentage of the Earth's surface is seen by all three sensors during a 24-hour period, taking into consideration sunlight, umbra, and how many times points on the ground are accessed. You also need to determine how long one satellite's sensor can cover Canada and the contiguous United States during the same interval.

Solution

Use the Coverage capability to model and analyze the quality and quantity of coverage provided by each of the sensors. Use figures of merit to determine the percentage of the Earth's surface the satellite payloads can survey in direct sun lighting conditions only during 24-hour period, how many times the sensor footprints can access points on the ground during that period, and for how long points on the ground can be seen in Canada and the contiguous United States.

What you will learn

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

  • Compute global and regional coverage using Coverage Definition objects
  • Understand a coverage grid
  • Determine coverage assets
  • Use constraints in a coverage grid
  • Evaluate the quality of coverage using Figure Of Merit objects
  • Visualize coverage with contour graphics in the 2D and 3D Graphics windows

Creating a new scenario

First, you must create a new scenario, then build from there.

  1. Launch the STK application ().
  2. Click Create a Scenario in the Welcome to STK dialog box.
  3. Enter the following options in the STK: New Scenario Wizard:
    4. Option Value
    Name STK_Coverage
    Location Default
    Start Default / set the time to 16:00:00.000 UTCG
    Stop + 24 hr
  4. Click OK when you finish.
  5. Click Save () when the scenario loads.

    6. The STK application automatically creates a folder with the same name as your scenario for you.

  6. Verify the scenario name and location in the Save As dialog box.
  7. Click Save.

Save () often!

Preparing your STK workspace

For this scenario, you will not use the Timeline View. Close it and configure your workspace.

  1. Close the Timeline View at the bottom of the STK workspace.
  2. Select the Window menu on the Menu Bar.
  3. Select Tile Vertically to have the 2D and 3D Graphics windows fill the workspace.

Turning off streaming terrain

By default, the STK application connects to the Ansys Geospatial Data Cloud to distribute Earth terrain data for analysis and visualization. Turn off streaming terrain to simplify your analysis for this scenario.

  1. Right-click on STK_Coverage () in the Object Browser.
  2. Select Properties () in the shortcut menu.
  3. Select the Basic - Terrain page when the Properties Browser opens.
  4. Clear the Use terrain server for analysis check box in the Terrain Server panel.
  5. Click OK to confirm your change and to close the Properties Browser.

Inserting the satellites

Insert three Satellite objects using the Orbit Wizard. The Orbit Wizard is a satellite-level tool designed to assist you in creating any one of several standard orbits, or designing your own satellite orbit. The configurable options available will depend on the orbit type selected.

Creating a satellite in a circular orbit

Circular orbits have a constant radius.

  1. Bring the Insert STK Objects tool () to the front.
  2. Select Satellite () in the Select An Object To Be Inserted list.
  3. Select Orbit Wizard () in the Select A Method list.
  4. Click Insert. . ..
  5. Leave the Type set to Circular when the Orbit Wizard opens.
  6. Enter Circ_Sat in the Satellite Name field.
  7. Set the following orbital elements in the Definition panel:
    8. Option Value
    Inclination 55 deg
    Altitude 700 km
    RAAN -105 deg
  8. Click OK to propagate Circ_Sat and to close the Orbit Wizard.

Creating a satellite in a repeating ground trace orbit

Insert a second satellite and place it in a repeating ground trace orbit. Orbits with repeating ground traces are useful when you want identical viewing conditions at different times to detect changes. You can have the ground trace repeat every day or interweave from day to day before repeating.

  1. Insert a Satellite () object using the Orbit Wizard () method.
  2. Open the Type drop-down list when the Orbit Wizard opens.
  3. Select Repeating Ground Trace.
  4. Enter Repeat_Sat in the Satellite Name field.
  5. Click OK to propagate Repeat_Sat and to close the Orbit Wizard.

Creating a satellite in a sun-synchronous orbit

Insert a third Satellite object and place it in a sun-synchronous orbit. These orbits are designed to utilize the effect of the Earth's oblateness, causing the orbital plane to precess at a rate equal to the mean orbital rate of the Earth around the Sun. Sun-synchronous orbits have the property that their nodes maintain constant local mean solar times.

  1. Insert a Satellite () object using the Orbit Wizard () method.
  2. Open the Type drop-down list when the Orbit Wizard opens.
  3. Select Sun Synchronous.
  4. Enter Sun_Sat in the Satellite Name field.
  5. Click OK to propagate Sun_Sat and to close the Orbit Wizard.

Adding the sensor payloads

All three satellites use the same sensor definition and field of view. Set up a sensor on one satellite, and then copy and paste it to the other two. The STK application enables you to copy and paste objects from one object to another.

Inserting a Sensor object

Attach a Sensor object to Circ_Sat.

  1. Insert a Sensor () object using the Define Properties () method.
  2. Select Circ_Sat () when the Select Object dialog box opens.
  3. Click OK to confirm your selection and to close the Select Object dialog box.

Setting the sensor definition

Use a Rectangular sensor definition with a 20-degree vertical half angle and 10-degree horizontal half angle. Rectangular sensor types are typically used with satellites or aircraft for modeling the field of view of instruments such as push broom sensors and star trackers.

  1. Select the Basic - Definition page when the Properties Browser opens.
  2. Open the Sensor Type drop-down list.
  3. Select Rectangular.
  4. Set the following options in the Rectangular panel:
    5. Option Value
    Vertical Half Angle 20 deg
    Horizontal Half Angle 10 deg
  5. Click OK to confirm your changes and to close the Properties Browser.

Reusing the Sensor object

Copy and paste the Sensor object onto the other two satellites.

  1. Select Sensor1 () in the Object Browser.
  2. Click Copy () on the Object Browser toolbar.
  3. Select Repeat_Sat () in the Object Browser.
  4. Click Paste () on the Object Browser toolbar.
  5. Select Sun_Sat () in the Object Browser.
  6. Click Paste () on the Object Browser toolbar.

Renaming the sensors

Rename all three Sensors objects.

  1. Right-click on Sensor1 () in the Object Browser.
  2. Select Rename in the shortcut menu.
  3. Rename Sensor1 () Circ_Sens.
  4. Repeat the process to Rename Sensor2 () Repeat_Sens.
  5. Rename Sensor3 () Sun_Sens.

Defining the coverage area

The STK software's Coverage capability allows you to analyze global or regional coverage provided by one or more assets such as facilities, vehicles, sensors, and so on, 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.

While you know what you want to study — the entire globe — you still need to specify it as your area of interest. Before performing a coverage analysis, you must first define your coverage area.

Inserting a Coverage Definition object

A Coverage Definition object enables you to define and maintain an area of interest, 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. Insert a Coverage Definition object into your scenario.

  1. Bring the Insert STK Objects tool () to the front.
  2. Insert a Coverage Definition () object using the Insert Default () method.
  3. Rename CoverageDefinition1 () World_Cov.
  4. Review the changes in the 2D Graphics window.

    5. 2D Graphics Window Default Coverage Grid

Note the orbit tracks of the three satellites.

The Coverage capability allows you to analyze numerous coverage areas simultaneously. Simply set up a Coverage Definition object for each area of interest. If you intend to analyze more than one set of contingencies for a given area, you can set up multiple Coverage Definition objects for that area, each representing a different set of contingencies.

Defining the coverage grid

Coverage analyses are based on access between assets — the objects that provide coverage — to geographical areas of interest. 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.

The default grid area of interest setting is Latitude Bounds, which specifies a grid between 60 degrees south latitude to 70 degrees north latitude. The point granularity defaults to every 6 degrees on the surface of the WGS84 ellipsoid. You can determine the spacing between grid points using grid definition options. These options help you define the fineness or coarseness of the grid. The use of finer grid resolutions typically produce more accurate results, but requires additional computational time and resources. Use the Grid properties to define your coverage grid to be global with a 4-degree point granularity.

  1. Open World_Cov's () Properties ().
  2. Select the Basic - Grid page when the Properties Browser opens.
  3. Open the Type drop-down list in the Grid Area of Interest panel.
  4. Select Global.

    5. This creates a grid that covers the entire globe. Due to the number of points computed when covering the globe, the time needed to calculate data when using this option may be large.

  5. Enter 4 deg in the Lat/Lon field in the Point Granularity panel.

    6. This determines the location of grid coordinates by applying the entered value. Grid points in longitude at higher or lower latitudes are stretched in an attempt to preserve the area of the grid point.

  6. Click Apply to confirm your changes and to keep the Properties Browser open.
  7. Select the 3D Graphics window to bring it to the front.
  8. Review the changes.

3D Graphics Window Global Coverage Grid

Notice the grid now covers the entire globe down to the poles.

Assigning coverage assets

A Coverage Definition object's Assets properties allow you to specify the STK objects used to provide coverage. Define the three Sensor objects as the Coverage Assets.

  1. Return to World_Cov's () Properties ().
  2. Select the Basic - Assets page.
  3. Expand () Circ_Sat (), Repeat_Sat () and Sun_Sat () in the Assets list.
  4. Multi-select Circ_Sens (), Repeat_Sens () and Sun_Sens () in the Assets list.
  5. Click Assign.

    6. Note that all three Sensor objects appear in bold with an asterisk (*) to the left of their names, which indicate they are currently assigned to the coverage area. Note also that the status of each Sensor object has been set to Active. Setting the status to Inactive enables you to remove selected assets from consideration without removing access information from the coverage calculations, and is typically useful after accesses have been computed. You can use the Inactive option to simulate the effect of an asset failure on the coverage provided by a set of satellites.

  6. Click Apply to confirm your changes and to keep the Properties Browser open.

While Sensor objects may be used as coverage assets, more time is required to compute accesses to them due to the need for finer sampling and attitude information. It is often possible to substitute constraints on either the grid points or the parent object of a Sensor object for the Sensor object itself to improve the performance of access computations.

Turning off the automatic recomputation of accesses

The STK application automatically recomputes accesses every time you update an object on which the coverage definition depends (such as an asset). If you want control as to when STK computes coverage, you need to turn this off by updating the Coverage Definition object's Advanced properties, which allow you to adjust the manner in which access information is stored and computed.

  1. Select the Basic - Advanced page.
  2. Clear the Automatically Recompute Accesses check box.
  3. Click OK to confirm your changes and to close the Properties Browser.

Computing coverage with 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 can compute coverage using the Compute Accesses tool. The Compute Accesses tool computes accesses between the grid points and the assigned assets.

  1. Select World_Cov () in the Object Browser.
  2. Select the CoverageDefinition menu on the Menu Bar.
  3. Select Compute Accesses.

The status of the access computations displays in the 2D Graphics window while accesses are being calculated. You can also view the progress of the computations in the Status Bar, located in the lower-right corner of the STK workspace.

Generating a coverage by latitude graph

The Coverage capability ships with several predefined report and graph styles that summarize key coverage information. A Coverage By Latitude graph is a quick way to see the percentage of time covered by latitude. It summarizes coverage for each latitude in the selected range (-90 degrees to 90 degrees for a Global coverage definition), at intervals depending on the selected resolution. The reported value for each latitude is the average value for all grid points at that latitude.

  1. Right-click on World_Cov () in the Object Browser.
  2. Select Report & Graph Manager... () in the shortcut menu.
  3. Select the Coverage By Latitude () graph style in the Installed Styles () folder, located in the Styles panel list, when the Report & Graph Manager opens.
  4. Click Generate. . ..
  5. Review the Coverage By Latitude graph.

    6. Coverage By Latitude Graph

    Note that there are two distinct latitude bands in each hemisphere that have significantly more coverage: one nearer the pole at 82 degrees latitude and one at 54 degrees latitude. This makes sense when you consider the earth's spherical geometry and the inclinations of the three Satellite objects.

  6. Close the Coverage By Latitude graph when finished.
  7. Click Close to close the Report & Graph Manager.

Evaluating simple coverage with a Figure Of Merit object

The STK application enables you to specify the method by which the quality of coverage is measured using a Figure Of Merit object. Figure Of Merit objects are extensions of the Coverage Definition object and, as a result, obtain their access information from their parent coverage definition. The Coverage Definition object defines the problem, while any Figure Of Merit objects provide methods for summarizing and viewing the resultant data.

Attaching a Figure Of Merit object to a Coverage Definition object

Attach a new Figure Of Merit object to your Coverage Definition object to evaluate the quality of coverage based on the available accesses. Note that accesses can only be computed for a Coverage Definition object.

  1. Bring the Insert STK Objects tool () to the front.
  2. Insert a Figure Of Merit () object using the Insert Default () method.
  3. Select World_Cov () when the Select Object dialog box opens.
  4. Click OK to confirm your selection and to close the Select Object dialog box.
  5. Rename FigureOfMerit1 () Simple_Cov.

Measuring Simple Coverage

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 criterion needed to achieve satisfactory coverage. You can specify the method by which the quality of coverage is measured using the options in the Figure Of Merit Definition page. The Simple Coverage method measures whether or not a point is accessible by any of the assigned assets during the analysis period. Areas on the map that are shaded mean that the surface point is seen by at least one sensor footprint during your 24-hour analysis period.

  1. Open Simple_Cov's () Properties ().
  2. Select the Basic - Definition page when the Properties Browser opens.
  3. Note the default Type is set to Simple Coverage in the Definition panel.
  4. Click Cancel to close the Properties Browser without making any changes.
  5. Bring the 2D Graphics window to the front.

    6. Simple Coverage Graphics

Your 2D Graphics window will look different than the image above. You can change the appearance of the shaded areas by updating Simple_Cov's () 2D Graphics - Static properties.

Generating a Percent Satisfied report

Using the Report & Graph Manager, you can generate several report and graph styles for a Figure Of Merit object. For this figure of merit, generate a Percent Satisfied report. This report presents the percentage of the total grid area where the static value of the Figure Of Merit object meets the specified satisfaction criterion. In this scenario, the report shows the percentage of the globe that is accessible by any of the three Sensor objects during the analysis period.

  1. Right-click on Simple_Cov () in the Object Browser.
  2. Select Report & Graph Manager... () in the shortcut menu.
  3. Select the Percent Satisfied () report style, located in the Installed Styles () folder, located in the Styles panel list, when the Report & Graph Manager opens.
  4. Click Generate. . ..
  5. Note the % Satisfied value at the bottom of the report.

    6. Approximately 77% of the globe is covered by at least one of the three sensors during the analysis time period.

  6. Close the Percent Satisfied report and the Report & Graph Manager when finished.

This baseline analysis does not take into any constraints that may exist, such as specific lighting conditions. In order to take constraints into account, you must first define them using a template object.

Constraining coverage

Once you have defined the grid area, you can specify an object class or a specific object for the points within the grid. The object can then be used to associate access constraints, which are factored into the computation of access times to restrict the periods of asset visibility, with the grid points. When you select a specific object, all of the properties and constraints that apply to that one object, excluding positional information, are also applied to every point in the grid.

Inserting a Target object as constraint template

Insert a Target object, which models a point of interest on the surface of the central body, and define a direct sun lighting constraint.

  1. Bring the Insert STK Objects tool () to the front.
  2. Insert a Target () object using Insert Default () method.
  3. Rename Target1 () Constraint_Template.

Adding a Direct Sun Lighting constraint

Basic constraints enable you to impose common access constraints on an object. You are interested in the coverage percentage during periods of total sunlight. Add a direct sun Lighting constraint to your Target object.

  1. Open Constraint_Template's () Properties ().
  2. Select the Constraints - Active page when the Properties Browser opens.
  3. Click Add new constraints () in the Active Constraints toolbar.
  4. Enter Lighting in the Search field when the Select Constraints to Add dialog box opens.
  5. Select Lighting in the Constraint Name list.
  6. Click Add.
  7. Click Close to close the Select Constraints to Add dialog box.
  8. Note that DirectSun is the default Value for the Lighting constraint.
  9. Click OKto confirm your changes and to close the Properties Browser.
  10. Clear the check box next to Constraint_Template () in the Object Browser.

You do not need to visualize the Constraint_Template Target object in the 2D or 3D Graphics windows in order to use it for a constraint template.

Applying the grid constraint

Use the Constraint_Template Target object as the grid constraint.

  1. Open World_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. Note that the Reference Constraint Class defaults to Target in the Grid Point Access Options panel when Grid Constraint Options dialog box opens.
  5. Select the Use Object Instance check box.
  6. Select Constraint_Template in the list.
  7. Click OK to confirm your changes and to close the Grid Constraints Options dialog box.
  8. Click OK to confirm your changes and to close the Properties Browser.

The constraints applied to a coverage analysis can be associated with the coverage assets or with the definition of the coverage area. While only one set of constraints can be associated with a Coverage Definition object, multiple Coverage Definition objects can be defined to model different constraints associated with the coverage area. You can see brief examples of situations where a single or multiple Coverage Definition objects are required here.

Recomputing accesses

Since a change was made to the coverage grid, you need to recompute accesses.

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

Simple Coverage with Direct Sun Constraint

Your 2D Graphics window will look different than the image above. It's obvious from the view in the 2D Graphics window that you have less coverage when using a Direct Sun constraint. Depending on the time of year, there may be more sunlight in the northern or southern hemisphere, which you can see represented in the coverage graphics.

Determining the coverage lost

Generate a new Percent Satisfied report to determine the percent coverage loss.

  1. Right-click on Simple_Cov () in the Object Browser.
  2. Select Report & Graph Manager... () in the shortcut menu.
  3. Select the Percent Satisfied () report style, located in the My Favorites () folder in the Styles panel list, when the Report & Graph Manager opens.
  4. Click Generate. . ..
  5. Note the % Satisfied value at the bottom of the report.

    6. Since coverage is now being analyzed during periods of direct sun and not being analyzed during periods of penumbra and umbra, there's a significant loss of coverage.

  6. Close the Percent Satisfied report and the Report & Graph Manager when finished.

Evaluating the Number of Accesses with another Figure of Merit object

You can attach multiple Figure Of Merit objects to a single Coverage Definition object to gauge different satisfaction criteria.

Attaching a new Figure Of Merit object to the Coverage Definition object

Attach a new Figure of Merit object to your Coverage Definition object to measure Number of Accesses to the individual points in the grid.

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

    2. This will clear its graphics from the 2D and 3D Graphics windows.

  2. Insert a Figure Of Merit () object using the Define Properties () method.
  3. Select World_Cov () when the Select Object dialog box opens.
  4. Click OK to confirm your selection and to close the Select Object dialog box.
  5. Select the Basic - Definition page when the Properties Browser opens.
  6. Open the Type drop-down list in the Definition panel.
  7. Select Number Of Accesses.
  8. Keep the default Compute type set to Total.

    9. The Total compute option computes the total number of accesses over the coverage interval without considering overlapping accesses.

  9. Click OK to confirm your changes and to close the Properties Browser.
  10. Rename FigureOfMerit2 () Num_Accesses.

Generating a Grid Stats report

Generate a Grid Stats report to see the smallest to largest number of accesses to any point in the grid. A Grid Stats report summarizes the minimum, maximum and average static value for the Figure Of Merit object over the entire grid.

  1. Right-click on Num_Accesses () in the Object Browser.
  2. Select Report & Graph Manager... () in the shortcut menu.
  3. Select the Grid Stats () report style, located in the Installed Styles () folder in the Styles panel list, when the Report & Graph Manager opens.
  4. Click Generate. . ..
  5. Note the Maximum value (for example, 8) when the Grid Stats report opens.

    6. A Maximum Value of 8 means at least one point in the grid was accessed on eight different occasions during the analysis period. Note that, as with Simple_Cov, the Num_Accesses figure of merit's Grid Stats report includes the constraints used by its parent coverage definition.

    The total number of accesses are computed over the coverage interval without considering overlapping accesses. A grid point with simultaneous access to two or more of the Satellite objects, even if the access to another Satellite object is entirely within the span of the access to the first Satellite object, would be measured as having two or more accesses.

  6. Note the Minimum value (for example, 0).

    7. A value of zero (0) means at least one point in the grid was never accessed by any of the three sensors during the analysis period.

  7. Close the Grid Stats report and the Report & Graph Manager when finished.
  8. Clear the check box next to World_Cov () in the Object Browser.

This will clear both the coverage grid and the figure of merit graphics in the 2D and 3D Graphics windows.

Focusing your coverage analysis

You can focus the coverage grid in a confined location by selecting custom regions for your grid area of interest. For this part of the analysis, you will focus on the contiguous United States (which excludes Alaska) and mainland Canada.

Creating Area Target objects for coverage

Insert two Area Target objects, which model regions on the surface of the central body, using the Select Countries and US States method.

  1. Bring the Insert STK Objects tool () to the front.
  2. Insert an Area Target () object using the Select Countries and US States () method.
  3. Clear the US States check box in the List Selections panel when the Select Countries And US States dialog box opens.
  4. Multi-select both Canada and United_States_of_America in the countries list on the left.
  5. Leave the Primary Area Only option selected in the Insert panel.

    6. The STK application creates Area Target objects from shapefiles, which contain one or more polygons. It converts each polygon into one Area Target object. If the shapefile for the selected area contains two or more polygons, you can choose whether to add only the largest polygon (Primary Area Only) or all polygons (All Areas) in the shapefile. By selecting this option, you will ignore islands and territories.

  6. Click Insert.
  7. Click Closeto close the Select Countries And US States dialog box.

Note that two separate Area Target objects have been created for both Canada and the United States of America.

Inserting a new Coverage Definition object

Insert a new Coverage Definition object.

  1. Insert a Coverage Definition () object using the Insert Default () method.
  2. Rename CoverageDefinition2 () Country_Cov.

Defining the coverage grid

Define the coverage area of interest to include Canada and the contiguous United States by selecting their Area Target objects. Area Target objects used to define custom regions should have a longitude span no greater than 180 degrees. This limitation includes area targets encompassing a polar region.

  1. Open Country_Cov's () Properties ().
  2. Select the Basic - Grid page when the Properties Browser opens.
  3. Open the Type drop-down list in the Grid Area of Interest panel.
  4. Select Custom Regions.
  5. Open the drop-down menu under Custom Regions.
  6. Select Area Targets.
  7. Multi-select both Canada () and United_States_of_America () in the Area Targets list on the left.
  8. Move () Canada () and United_States_of_America () from the Area Targets list to the Selected Regions list.
  9. Enter 1 deg in the Lat/Lon field in the Point Granularity panel.

    10. When using custom regions, it is important to select adequate point granularity. If a single custom region is smaller than the resolution, the STK application will generate an alternative grid using a finer granularity to ensure at least three samples within the region.

  10. Click Apply to confirm your changes and to keep the Properties Browser open.

Viewing the changes in the 2D Graphics window

View the inlaid grids in the 2D Graphics window.

  1. Bring the 2D Graphics window to the front.
  2. Zoom In () so that you only see Canada and United States.

Coverage Grid Confined to Area Targets

Your 2D Graphics window will appear different than the image above. If desired, you can Zoom In () and center the 3D Graphics window to the same view as the 2D Graphics window.

Assigning the coverage asset

Assign the Sensor object on the Satellite object with a repeating ground trace orbit as the asset for the Coverage Definition object.

  1. Return to Country_Cov's () Properties ().
  2. Select the Basic - Assets page.
  3. Expand () Repeat_Sat () in the Assets list.
  4. Select Repeat_Sens () in the Assets list.
  5. Click Assign.
  6. Click Apply to confirm your changes and to keep the Properties Browser open.

Turning off grid points

You can define how the coverage grid displays in the 2D Graphics window by opening the 2D Graphics Attributes for the Coverage Definition object of interest. You will be displaying Figure Of Merit object graphics, so turn off the grid point display for easier viewing.

  1. Select the 2D Graphics - Attributes page.
  2. Clear the Show Points check box in the Grid panel.

    3. This turns off the visual grid inside the Area Target objects. Analytically, they're still there.

  3. Click OK to confirm your changes and to close the Properties Browser.

Computing accesses

With your regions selected and assets assigned, compute the accesses.

  1. Right-click on Country_Cov () in the Object Browser.
  2. Select CoverageDefinition in the shortcut menu.
  3. Select Compute Accesses in the CoverageDefinition submenu.

Measuring Coverage Time with another Figure Of Merit object

Use a Coverage Time Figure Of Merit object to determine the amount of time during which the grid points are covered by Repeat_Sens.

Inserting a Figure of Merit object

Insert a Figure Of Merit object to measure the quality of coverage of Country_Cov.

  1. Insert a Figure Of Merit () object using the Insert Default () method.
  2. Select Country_Cov () when the Select Object dialog box opens.
  3. Click OK.to confirm your selection and to close Select Object dialog box.
  4. Rename the FigureOfMerit3 () Cov_Time.

Measuring Coverage Time

Set the Figure Of Merit object to 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. Open Cov_Time's () Properties ().
  2. Select the Basic - Definition page when the Properties Browser opens.
  3. Open the Type drop-down list in the Definition panel.
  4. Select Coverage Time.
  5. Open the Compute drop-down list.
  6. Select Total.

    7. This will compute the amount of time (over the entire coverage interval) during which a point is covered.

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

Generating a Grid Stats report

Generate a Grid Stats report to determine the minimum and maximum amount of time any of the grid points are covered by Repeat_Sens.

  1. Right-click on Cov_Time () in the Object Browser.
  2. Select Report & Graph Manager... () in the shortcut menu.
  3. Select the Grid Stats () report style, located in the My Favorites () folder in the Styles panel list, when the Report & Graph Manager opens.
  4. Click Generate....
  5. Note the Maximum (sec) when the Grid Stats report opens (for example, approximately 49 seconds).

    6. That means at least one point in the grid was accessed for an approximate total of 49 seconds during the analysis period.

  6. Keep your Grid Stats report open.

Defining static graphics for the Figure Of Merit object

Define static graphics for the Figure Of Merit object on the 2D Graphics - Static page.

  1. Return to Cov_Time's () Properties ().
  2. Select the 2D Graphics - Static page.
  3. Enter 30 in the % Translucency field in the Show Points As panel.

Showing contours

You can specify how levels of coverage quality display in both the 2D and 3D Graphics windows. To accurately display contour levels for a Figure Of Merit object in the 2D and 3D Graphics window, you should know the approximate range of values for the current Figure Of Merit object. You can use the Report & Graph Manager for the Figure Of Merit object to determine this range. Defining contour levels for display in the 2D and 3D Graphics windows requires several steps. Start by defining the number and type of contour levels to be displayed.

  1. Select the Show Contours option in the Display Metric panel.
  2. Click Remove All in the Level Attributes panel.
  3. Set the following in the Level Adding panel:
    4. Option Value
    Start 0 sec
    Stop round down to the nearest integer from the Maximum (sec) value in the Grid Stats report (for example, 49 sec)
    Step 5 sec
  4. Click Add Levels.
  5. Open the Start Color drop-down list in the Level Attributes panel.
  6. Select red.
  7. Open the End Color drop-down list.
  8. Select blue.

    9. Points with no coverage will be red and any points at or above your highest Level Attribute value will be blue.

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

    10. Color is applied smoothly over all points in the grid to differentiate contour levels.

  10. Click Apply to confirm your changes and to keep the Properties Browser open.

Configuring legends for the 2D and 3D Graphics windows

Once you have set the contours for coverage, you choose to display a contour key, or legend in your 2D and/or 3D Graphics window. A Legend provides you with a convenient way to interpret contour data displayed in the 2D and 3D Graphics windows.

Using the Contours Legend tool

The Figure of Merit Legend Layout dialog box 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).

  1. Click Legend... in the Level Attributes panel.
  2. Click Layout... when the Contours Legend window opens.
  3. Select the Show at Pixel Location check box in the 2D Graphics Window panel when the Figure of Merit Legend Layout dialog box opens.
  4. Select the Show at Pixel Location check box in the 3D Graphics Window panel.

    5. These options define the pixel location for the upper-left corner of the legend in the two windows. The pixel location is used to maintain the location of the legend regardless of the zoom level.

  5. Set the following options in the Text Options panel:
    6. Option Value
    Title Coverage Time (seconds)
    Number Of Decimal Digits 0

    The Title contains the text displayed at the top of the contours legend. The Number Of Decimal Digits specifies the number of digits that should be displayed to the right of the decimal point for real numbers.

  6. Enter 50 in the Color Square Width (pixels) field in the Range Color Options panel.

    7. This specifies the width (in pixels) of the individual color bands in the legend. Setting this to 50 makes them easier to see.

  7. Click OK to confirm your changes and to close the Figure of Merit Legend Layout dialog box.
  8. Close Contours Legend window.
  9. Click OK to confirm your changes and to close the Properties Browser.

Viewing the legends

With your legends and contours configured, view them in the 2D and 3D Graphics windows.

  1. Bring the 2D window to the front.
  2. Note the contours and placement of the legend.

    3. 2D Graphics Window with Coverage Contours

    Your contour graphics will look different than those show in the image above. You can see that there are distinct tracks where Repeat_Sens was able to access the coverage area. In several instances, the tracks cross, leading to relatively high total coverage times.

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

    4. 3D Graphics Window with Coverage Contours

    Your contour graphics will look different than those show in the image above.

  4. Note the contours are the same in both windows.

Saving your work

Clean up and close out your scenario.

  1. Close any open graphs, properties, and tools.
  2. Save () your work.

Summary

This tutorial served as an introduction to the STK software's Coverage capability. You began by modeling satellites in three different orbits and attaching identical sensor payloads to each. You inserted a Coverage Definition object and updated its properties to cover the entire globe. You then computed access and examined the coverage by latitude. After inserting a Figure Of Merit object to examine simple coverage, you applied a lighting constraint to the coverage definition with a template object to evaluate the effect on the overall coverage. You then examined the quality of coverage using a separate Figure Of Merit object to examine the number of accesses. You next inserted two Area Target objects, together with another Coverage Definition object and Figure Of Merit object, to evaluate the coverage time provided by a single sensor over the contiguous United States and Canada. Finally, you added static contour graphics for the Figure Of Merit object to of the coverage data to visualize the coverage data in the 2D and 3D Graphics windows.

On your own

Coverage analyses can come in many forms and types. The following tutorials are recommended for further training: