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 training by contacting AGI Support at support@agi.com or 1-800-924-7244.

This lesson requires STK 12.7 or newer to complete.

Pictures, graphs, and data snippets are used as examples only. 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

Problem statement

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

Solution

Use STK to model a large constellation of satellites using the Satellite Collection object and SP3 files. Use STK Coverage to determine dilution of precision over the Continental United States during a selected analytical period.

What you will learn

Upon completion of this tutorial, you will understand:

  • How to implement the Satellite Collection object.
  • How to use SP3 files.
  • How to analyze dilution of precision using STK's Coverage capabilitiy.

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 STK scenario and then build from there.

  1. Launch STK ().
  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. STK creates a folder with the same name as your scenario for you.
  6. Verify the scenario name and location in the Save As window.
  7. Click Save.

Save () often during this lesson!

Inserting a Satellite Collection object

The 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 STK's Coverage capability, CommSystem, DeckAccess, and AdvCAT.

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

Using SP3 files

Extended Standard Product (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.

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

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

Loading your SP3 file

You need to select your SP3 file location.

  1. Click the Ephemeris Directory ellipsis () located in the SP3 Properties frame.
  2. Browse to the SP3 file (typically: <STK install folder>\Data\Resources\stktraining\samples\Ephemeris) in the Select File dialog box.
  3. Click Select Folder.
  4. Click OK to accept your changes and to close the Properties Browser.
  5. Open SP3_Collection's () properties ().
  6. Make a note of the Start and Stop times of the file.

    • Start: 13 May 2023 23:59:42.000 UTCG

    • Stop: 15 May 2023 00:04:42.000 UTCG

Viewing available subsets

STK 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 (e.g., GPS-Block_IIF).

  1. Scroll down through the list to view your satellites in the Subsets frame.

Editing the Graphics Attributes properties

You only want to view the GPS satellites in the 3D Graphics window.

  1. Select the Graphics - Attributes page.
  2. Clear the Show check box for AllSatellites.
  3. Select the Show checkbox for the following satellites:

    • 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 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 frame:
    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 Area Target () objects. For this part of the analysis, you will focus on the continental United States. Islands and territories will not be taken into consideration.

Insert an Area Target () to model the Continental United States.

  1. Insert an Area Target () object using the Select Countries and US States () method.
  2. Clear the US States checkbox in the List Selections frame 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 (). Insert a Coverage Definition () object.

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

Defining the grid area of interest

Define the coverage area of interest to be the continental 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 menu in the Grid Area of Interest frame.
  4. Select Custom Regions.
  5. Select Area Targets in the drop-down menu 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 frame.
  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 Continental 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 satellites:

    • 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 Figure Of Merit graphics, so turn off the grid point display.

  1. Go to the 2D Graphics - Attributes page.
  2. Clear the Show Points checkbox in the Show - Grid field. 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 (e.g., Sensor object field of view) upon those accesses.

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

Determining the quality of coverage

You can evaluate the quality of coverage for an area by creating one or more Figure Of Merit () objects 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 () to GDOP.

Adding geometric dilution of precision (GDOP) as the FOM

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. 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.
  1. Open GDOP's () properties ().
  2. Go to the Basic - Definition page when the Properties Browser opens.
  3. Open the Type: shortcut menu in the Definition frame.
  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 the 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 GDOP () in the Object Browser.
  2. Select Report & Graph Manager ().
  3. Select the Grid Stats report () in the Installed Styles list when the Report & Graph Manager opens.
  4. Click Generate....
  5. Note the Maximum value (e.g., 2.745).

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

  6. Return to GDOP's () properties().
  7. Open the Compute: shortcut menu in the Definition frame.
  8. Select Minimum.
  9. Click Apply to accept your changes and to keep the Properties Browser open.

Refreshing the report

  1. Return to the Grid States report.
  2. Click Refresh (F5) () in the report toolbar.
  3. Note the Minimum value (e.g., 1.037).

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

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

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

Defining animation graphics for the Figure Of Merit

In the Figure of Merit properties, the 2D Graphics - Animation page enables 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 frame.
  4. Select the Show Contours option in the Display Metric frame.
  5. Click Remove All in the Level Attributes frame.
  6. Enter the following in the Level Adding frame located in the Levels frame:
    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 frame:
    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) frame.
  10. Click Apply to accept your changes and keep the Properties Browser open.

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

Viewing the coverage in the 2D graphics window.

You can view GDOP coverage in both the 2D and 3D Graphics windows. You will use the 2D Graphics window.

  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 fro◘nt, zoom to the Continental United States, and animate your scenario.

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 one Satellite Collection () object containing multiple GPS satellites.
  • Use the selected GPS satellites to perform GDOP coverage over the Continental 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

Saving your work

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