Satellite Collection Object: Using SP3 Files

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.

This lesson requires version 12.7 of the STK software or newer to complete.

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

  • STK Pro
  • Coverage

Problem statement

You require a fast, easy way to set up and analyze a group of satellites as a single object using an SP3 file. You also need to simulate and analyze dilution of precision using GPS satellites.

Solution

Use the STK software to model a large constellation of satellites using a Satellite Collection object and an SP3 file. Use the STK software's Coverage capability to determine dilution of precision over the contiguous United States during a selected analytical period.

What you will learn

Upon completion of this tutorial, you will understand:

  • How to use a Satellite Collection object
  • How to use SP3 files
  • How to analyze dilution of precision using the STK software's Coverage capability

Video guidance

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

Creating a new scenario

First, you must create a new scenario and 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 in the STK: New Scenario Wizard:
    4. Option Value
    Name GPS_SP3
    Location Default
    Start Default
    Stop Default
  4. Click OK when you finish.
  5. Click Save () when the scenario loads. The STK software 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 during this lesson!

Inserting a Satellite Collection object

A Satellite Collection object models a group of satellites as a single object in the Object Browser. The associated satellites do not appear in the Object Browser, but are available for analysis purposes within other computational tools such as the STK software's Coverage capability, CommSystem objects, and the Deck Access and Advanced CAT tools.

  1. Select SatelliteCollection () in the Insert STK Objects Tool.
  2. Select Insert Default () as the method.
  3. Click Insert....
  4. Right-click on SatelliteCollection1 () in the Object Browser.
  5. Select Rename in the shortcut menu.
  6. Rename SatelliteCollection1 () SP3_Collection.

Using SP3 files

Use the Basic - Definitions page of the satellite collection properties to define its members and subsets. The STK software constructs the group of satellites based on the type that you choose. The SP3 Satellite Collection definition allows you to make use of Extended Standard Product (SP3) files. SP3 files contain detailed orbit information for the satellites in different GNSS systems. The information contained in the SP3 files consists of precise orbit data and precise clock corrections with the associated errors for the satellites in the files.

  1. Right-click on SP3_Collection () in the Object Browser.
  2. Select Properties () in the shortcut menu.
  3. Go to the Basic - Definition page when the Properties Browser opens.
  4. Open the Type drop-down list.
  5. Select SP3.

    6. For this option, you provide search parameters for the STK application to apply in extracting satellites for the collection from an SP3 file.

Loading an SP3 file

An SP3 file (RAM23134.SP3) has been provided for you in the STK software install. You must select its file location as the ephemeris directory to make use of it.

  1. Click the Ephemeris Directory ellipsis () located in the SP3 Properties panel.
  2. Browse to the location of the SP3 file at <Install Dir>\Data\Resources\stktraining\samples\Ephemeris) when the Select File dialog box opens.
  3. Click Select Folder.
  4. Click OK to accept your changes and to close the Properties Browser.

Viewing the SP3 file's details

Open the Satellite Collection object's properties to view details loaded from the SP3 file.

  1. Open SP3_Collection's () Properties ().
  2. Make a note of the Start and Stop times of the file. You will need them later.
    • Start: 13 May 2023 23:59:42.000 UTCG
    • Stop: 15 May 2023 00:04:42.000 UTCG
  3. Scroll down through the list to view your satellites in the Subsets panel.

    4. The STK software will automatically generate a subset called AllSatellites for each selected type. Using the SP3 type, you will also have a subset for each satellite constellation (for example, GPS-Block_IIF).

Editing the Graphics Attributes properties

You only want to view the GPS satellites in the 3D Graphics window. You can control the graphical display of a satellite collection by updating the Satellite Collection's Graphics Attributes.

  1. Select the Graphics - Attributes page.
  2. Clear the Show check box for the AllSatellites subset.
  3. Select the Show check box for the following satellite subsets:
    • GPS-Block_IIF
    • GPS-Block_III
    • GPS-Block_IIR
    • GPS-Block_IIIRM
  4. Change the color, if desired.
  5. Click OK to accept your changes and to close the Properties Browser.

Changing the analysis start and stop times

You need to reset your scenario analysis period to match the start and stop times of the SP3 file.

  1. Open GPS_SP3's () Properties ().
  2. Go to the Basic - Time page when the Properties Browser opens.
  3. Set the following in the Analysis Period panel:
    4. Option Value
    Start 13 May 2023 23:59:42.000 UTCG
    Stop 15 May 2023 00:04:42.000 UTCG
  4. Click OK to accept your changes and to close the Properties Browser.

Viewing the satellites in the 3D Graphics window

Reset your scenario to the new analysis period.

  1. Bring the 3D Graphics window to the front.
  2. Click Reset () in the Animation Toolbar.
  3. Use your mouse to zoom out until you can see the constellation of satellites.
  4. Click Start () in the Animation toolbar to animate your scenario.
  5. Click Reset () in the animation toolbar once you finish viewing your constellation of satellites.

Adding an Area Target

You can focus the coverage grid in a confined location using an Area Target object. For this part of the analysis, you will focus on the contiguous United States. Islands and territories will not be taken into consideration. Insert an Area Target to model the contiguous United States.

  1. Insert an Area Target () object using the Select Countries and US States () method.
  2. Clear the US States check box in the List Selections panel when the Select Countries And US States dialog box opens.
  3. Select United_States_of_America in the countries list on the left.
  4. Click Insert.
  5. Click Close.

Creating a new Coverage Definition

You want to determine coverage inside the boundaries of United_States_of_America. Do so by inserting a Coverage Definition object.

  1. Insert a Coverage Definition () object using the Insert Default () method.
  2. Rename CoverageDefinition1 () DilutionOfPrecisionCov.

Defining the grid area of interest

Define the coverage area of interest to be the contiguous United States using the Area Target.

  1. Open DilutionOfPrecisionCov's () Properties ().
  2. Go to 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. Select Area Targets in the drop-down list below Custom Regions.
  6. Select United_States_of_America () in the Area Targets list.
  7. Move () United_States_of_America () to the Selected Regions list.

Specifying the grid definition

The statistical data computed during a coverage analysis is based on a set of locations, or points, which span your grid area of interest.

  1. Enter 1 deg in the Point Granularity - Lat/Lon field in the Grid Definition panel.
  2. Click Apply to accept your changes and to keep the Properties Browser open.
  3. Bring the 2D Graphics window to the front.
  4. Zoom In () so that you only see the contiguous United States.

Choosing your assets

Assets properties enable you to specify the STK objects used to provide coverage.

  1. Return to DilutionOfPrecisionCov's () Properties ().
  2. Go to the Basic - Assets page.
  3. Expand () SP3_Collection () in the Assets list.
  4. Select the following satellite subsets ():
    • GPS-Block_IIF
    • GPS-Block_III
    • GPS-Block_IIR
    • GPS-Block_IIIRM
  5. Click Assign.
  6. Click Apply to accept your changes and to keep the Properties Browser open.

Turning off grid display

You will display the Figure of Merit graphics, so turn off the grid point display.

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

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

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

Computing coverage

The ultimate goal of coverage is to analyze accesses to an area using assigned assets and applying necessary limitations (for example, Sensor object field of view) upon those accesses.

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

Determining the quality of coverage

You can evaluate the quality of coverage for an area by creating a Figure of Merit object attached to the Coverage Definition object of interest.

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

Adding a geometric dilution of precision Figure of Merit

Dilution of Precision (DOP) measures the relative degradation or reduction in the certainty of a navigation solution based on one-way range measurements from a set of transmitters. Most often, the transmitters are those on board Global Positioning System (GPS) satellites. If four or more of these satellites are in view of a ground receiver, a navigation solution consisting of the position of the receiver and the offset between the receiver clock and the GPS clock can be computed. You can interpret the dilution of precision using the following:

    DOP value Rating Description
    < 1 Ideal This is the highest possible confidence level, for applications demanding the highest possible precision at all times.
    1-2 Excellent Positional measurements are considered accurate enough to meet all but the most sensitive applications.
    2-5 Good This marks the minimum for making accurate decisions.
    5-10 Moderate You can use the positional measurements for calculations, but you should look to improve.
    10-20 Fair This is a low confidence level, used mostly for a rough estimate of the current location.
    > 20 Poor You should discard all measurements.

Dilution of precision can be calculated in a number of ways, depending on your task. Geometric dilution of precision (GDOP) measures the dilution of precision for the entire navigation solution. GDOP combines the dilution of the position and clock-related components of the navigation solution. A GDOP of less than one (1) is possible.

A DOP Figure of Merit measures the effects of the number of measurements and the geometry of the transmitters on the uncertainty in the navigation solution. The reported value can be multiplied by the uncertainty in the range measurements (assumed to be the same for all transmitters) to provide the uncertainty in the navigation solution.

  1. Open GDOP's () Properties ().
  2. Go to the Basic - Definition page when the Properties Browser opens.
  3. Open the Type drop-down list in the Definition panel.
  4. Select Dilution Of Precision.
  5. Set the following parameters:
    6. Option Value
    Compute Maximum
    Method GDOP
    Type Over Determined
    Time Step 60 sec
  6. Click Apply to accept your changes and to keep the Properties Browser open.

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.

  1. Right-click on GDOP () in the Object Browser.
  2. Select Report & Graph Manager... () in the shortcut menu.
  3. Select the Grid Stats () report in the Installed Styles list when the Report & Graph Manager opens.
  4. Click Generate....
  5. Scroll to the bottom of the report.
  6. Note the Maximum value (for example, 2.745).

    7. That means at least one point in the grid had a maximum GDOP of approximately 2.75.

  7. Return to GDOP's () Properties().
  8. Open the Compute drop-down list in the Definition panel.
  9. Select Minimum.
  10. Click Apply to accept your changes and to keep the Properties Browser open.

Refreshing the Grid Stats report

Refresh your Grid Stats report to view the GDOP.

  1. Return to the Grid States report.
  2. Click Refresh (F5) () in the report toolbar.
  3. Scroll to the bottom of the report.
  4. Note the Minimum value (for example, 1.037).

    5. That means at least one point in the grid point had a minimum GDOP of approximately 1.037.

  5. Close () the report when finished.
  6. Close () the Report & Graph Manager.

Overall, you obtained good to excellent GDOP values during the analysis.

Defining animation graphics for the Figure of Merit

Graphics are used to represent the static and dynamic value of Dilution of Precision. The Figure of Merit 2D Graphics Animation properties enable you to define animation graphics for the Figure Of Merit data.

  1. Return to GDOP's () properties ().
  2. Go to the 2D Graphics - Animation page.
  3. Enter 30 in the % Translucency field in the Show Points As panel.
  4. Select the Show Contours option in the Display Metric panel.
  5. Click Remove All in the Level Attributes panel.
  6. Enter the following in the Level Adding panel located in the Levels panel:
    7. Option Value
    Start 1 (rounded down)
    Stop 2.7 (rounded down)
    Step 0.1
  7. Click Add Levels.
  8. Set the following in the Level Attributes panel:
    9. Option Value
    Color Method Color Ramp
    Start Color Blue (best value)
    End Color Red (worst value)
  9. Select the Natural Neighbor option in the Contour Interpolation (points must be filled) panel.
  10. Click Apply to accept your changes and keep the Properties Browser open.

Configuring the 2D and 3D Graphics window legends

Once you have set the contours for coverage, you can set the display of the contour key, or legend.

  1. Click Legend....
  2. Click Layout... in the Animation Legend for GDOP dialog box.
  3. Set the following on the Figure of Merit Legend Layout dialog box:
    4. Option Value
    2D Graphics Window - Show at Pixel Location Selected
    3D Graphics Window - Show at Pixel Location Selected
    Text Options - Title GDOP Values
    Text Options - Number Of Decimal Digits 1
    Range Color Options - Color Square Width (pixels) 50
  4. Click OK to confirm your changes and to close the Figure of Merit Legend Layout dialog box.
  5. Close () the Animation Legend for GDOP dialog box.
  6. Click OK to close GDOP's () Properties ().

Viewing dynamic GDOP coverage in the 2D Graphics window

Graphics representing dynamic DOP values are only displayed while the scenario is animated. You can view the GDOP coverage in both the 2D and 3D Graphics windows. You will use the 2D Graphics window for this exercise.

  1. Bring the 2D Graphics window to the front.
  2. Click Increase Time Step () in the Animation toolbar to set Time Step to 60 sec.
  3. Click Start () to animate your scenario.

    4. You are viewing GDOP changes during the selected analytical time period of your scenario.

  4. Click Reset () in the Animation toolbar once you are done.
  5. If you desire, you can bring the 3D Graphics window to the front, zoom to the contiguous United States, and animate your scenario.

Saving your work

Clean up your workspace and close out your scenario.

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

Summary

This was a comprehensive scenario that showed you how to use the Satellite Collection object and SP3 files. You learned how to:

  • Use SP3 files to create a Satellite Collection object containing multiple GPS satellites
  • Use the selected GPS satellites to perform GDOP coverage over the contiguous United States
  • Obtain the minimum and maximum GDOP values from the Report & Graph Manager
  • Set up contours and view GDOP in both the 2D and 3D Graphics windows