Creating Color Elevation Imagery and Using Raw Satellite Imagery

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 Ansys Systems Tool Kit^® (STK^®) digital mission engineering software or newer to complete in its entirety. If you have an earlier version of the STK software, you can complete a legacy version of this lesson.

Capabilities covered

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

STK Pro

Problem statement

Engineers and operators require a quick and easy way to determine if local terrain is affecting visibility between ground sites and satellites for a variety of purposes, such as communications, imaging, and general situational awareness. You are studying a GPS-enabled monitoring station in the vicinity of Mount St. Helens. You have a U.S. Geological Survey (USGS) Digital Elevation Model (DEM) file containing terrain data for the area requiring analysis. Raw satellite imagery is available of Mount St. Helens, which can provide situational awareness of the analytical area. A further need exists to create color elevation imagery of the area to be used in a briefing and in documentation.

Solution

Load a local terrain file to analyze the impact of local terrain on accesses between a ground station and GPS satellites. Create a color elevation image and convert a raw satellite image that can be used as an inlay for visualization and situational awareness. Change the DEM file into a STK Terrain Inlay (PDTT) file, which can be used to visualize terrain in the 3D Graphics window. Finally, insert the GPS constellation and use it in a Chain object, together with the analytical terrain and an azimuth-elevation mask, to model access to the monitoring station.

What you will learn

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

Use local terrain files for analysis
Create and customize color elevation imagery using the Create Color Elevation Imagery utility
Convert a single, georeferenced image into a format that can be displayed in the 3D Graphics window using the Imagery and Terrain Converter
Create terrain inlays for a specific region using the Terrain Region Converter
Model and visualize an azimuth-elevation mask with the local terrain to constrain access between objects

Creating a new scenario

First create a new scenario, the build from there.

Launch the STK application ().
Click Create a Scenario in the Welcome to STK dialog box.
Enter the following in the STK: New Scenario Wizard:

Option	Value
Name	Imagery_Raw
Start	Use the default date / set the time to 19:00.00.000 UTCG
Stop	+ 24 hr

Click OK when you finish.
Click Save () when the scenario loads.

The STK software creates a folder with the same name as your scenario for you.

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

Save () often during this lesson!

Locating the U.S. Geological Survey DEM file

The USGS DEM file file used in this tutorial is located in a compressed (zipped) file the STK software installation directory.

Do not extract (unzip) the file.

Using Windows File Explorer, browse to the location of the zipped DEM file in the STK software installation directory at C:\Program Files\AGI\STK_ODTK 13\CodeSamples.
Double-click on STKCodeSamples.zip to open it without extracting.
Once inside STKCodeSamples.zip, navigate to SharedResources\Scenarios\Events within the zipped file.
Locate the hoquiam-e.dem file.
Copy the hoquiam-e.dem file, again, without extracting.
Navigate to the location of your scenario folder (for example, C:\Users\<username>\Documents\STK_ODTK 13\Imagery_Raw).
Paste the hoquiam-e.dem file into your scenario folder.
Close Windows File Explorer.

This is a different preinstalled DEM file than hoquiam-e.dem, located in <Install Dir>\Data\Resources\stktraining\samples, which has a similar resolution but a smaller overall extent.

Importing terrain data into a scenario

Use the Scenario object's Terrain properties to use the DEM file you copied into your scenario folder for analysis and visualization.

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, as you want to use a local file to model the terrain data.

Return to the STK Application.
Right-click on Imagery_Raw () in the Object Browser.
Select Properties () in the shortcut menu.
Select the Basic - Terrain page when the Properties Browser opens.
Clear the Use terrain server for analysis check box in the Terrain Server panel.
Click Apply to confirm your change and to keep the Properties Browser open.

Using a custom analysis terrain source

The DEM file you extracted contains digital elevation data for Mount St. Helens and the vicinity near the city of Hoquiam, Washington.

Click Add in the Custom Analysis Terrain Sources panel.
Open the file type drop-down list when the Open dialog box opens.
Select USGS DEM (DEM) (*.dem).
Browse to your scenario folder (for example, C:\Users\<username>\STK_ODTK 13\Imagery_Raw).
Select hoquiam-e.dem.
Click Open to select the file and to close the Open dialog box.
Click OK to confirm your selection and to close the Properties Browser.
Save () your scenario.

Updating the 2D Graphics window

Customize the 2D Graphics window by modifying its properties.

Displaying a background image and inlay in the 2D Graphics window

Update the 2D Graphics window's Imagery properties to display a basic background image.

Bring the 2D Graphics window to the front.
Click Properties () on the 2D Window Defaults toolbar.
Select the Imagery page when the Properties Browser opens.
Select the Image File option in the Background Image panel.
Ensure Basic.bmp is selected in the Image File.

Basic.bmp is a 2048 × 1024 bitmap file. It is included with other background images in the STK software installation. They are stored in the <Install Dir>\STKData\CentralBodies\Earth\Pixmaps folder.

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

If you don't have an Internet connection, the Basic.bmp is the default background image. You can also choose add your own custom background imagery in this manner.

Displaying borders and terrain extents in the 2D Graphics window

Update the 2D Graphics Details properties to show bother international borders and those of the states of the United States and provinces of Canada and to create an outline of the extent of the hoquiam-e.dem file in the 2D Graphics window.

Select the Details page.
Select the following in the Map Details list n addition to RWDB2_Coastlines:

RWDB2_International_Borders
RWDB2_Provincial_Borders

Select the Show Extents check box in the Terrain Regions Display panel.

When enabled, an outline displays around imported terrain region (hoquiam-e.dem) on the map.

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

Viewing the changes in the 2D Graphics window

View your changes to the 2D Graphics window.

Bring the 2D Graphics window to the front.
Zoom In () to the northwestern United States.

Terrain Extents, with Extent Border Emphasized for clarity

The yellow box in the southwest corner of Washington State is the location of the hoquiam-e.dem file. Analysis inside the box can be done using local terrain. Analysis outside the box will take place on the surface of the WGS84 ellipsoid — that is, the altitude is set to 0.0.

Zoom In () to the extent of the analytical terrain.

Creating a color elevation image

The Create Color Elevation Imagery utility allows you to create images from terrain data to show elevation data colored by height — for example, blue for sea level, green for land, and white for mountaintops. This is useful if you need to visualize terrain but lack imagery or if you want to put the emphasis on height rather than the content of the image.

Opening the Create Color Elevation Imagery utility

Open the Create Color Elevation Imagery utility from the Menu Bar.

Select the Utilities menu in the Menu Bar.
Select Create Color Elevation Imagery....
Move the Create Color Elevation Imagery utility so that it doesn't block the terrain region display.

Specifying the terrain region

Start by specifying the terrain region containing the terrain to be converted. The STK application uses any valid terrain sets included in the selected region. If more than one terrain set is valid for a region, the STK application uses the terrain set with the highest-available resolution. If the region contains no terrain data, an image will not be created.

Enter the following extents, which match the extents of hoquiam-e.dem, in the Terrain Region panel when the Create Color Elevation Imagery utility opens:

Option	Value
North Lat	47 deg
West Lon	-123 deg
East Lon	-122 deg
South Lat	46 deg

Click Get Min/Max Alt.

This displays estimated minimum and maximum altitude values of the region selected in the 2D Graphics window. This range can help you, especially if you use explicit colors. When the region is actually converted, the minimum and maximum values will be updated with their true values.

Setting the color options

When you generate a color elevation image, the resulting image is colored so that elevations are drawn with a linearly interpolated color between the minimum altitude and the maximum altitude, depending on the elevation. By default, color elevation images are generated using the HSV (Hue, Saturation, Value) color input method, which produces a wider range of colors than the RGB method.

The default values for Hue, Saturation, and Value will display dark blue at the lowest altitude, green at the mid-point, and white at the highest altitude. You are landlocked, so change the Min Altitude's corresponding HSV value that changes the blue "base" color at the lowest altitudes with black.

Set the following Min Altitude values in the Color Options panel:

Option	Value
Hue	0.2500
Saturation	0.7500
Value	0.2000

Ensure JPEG 2000 Image (jp2) is selected for the Format in the Output File panel.
Ensure the Create a pdtt file for the selected region check box is cleared.

You will use the Terrain Region Converter to convert your terrain data to a terrain inlay for this tutorial.

Click the Directory ellipsis ().
Browse to the location of your scenario folder (e.g. C:\Users\<username>\Documents\STK_ODTK 13\Imagery_Raw) when the Directory dialog box opens.
Click Select Folder to confirm your selection and to close the Director dialog box.
Enter StHelensColor in the Filename field.
Click Convert.
Click Close to close the Create Color Elevation Imagery utility.

Inlaying the color elevation image in the 2D Graphics window

Update the 2D Graphics window's Imagery properties to inlay the color elevation image.

Return to the 2D Graphics window's Properties ().
Select the Imagery page.
Click Add... in the Inlay Images panel.
Select StHelensColor.jp2 when the Map Images dialog box opens.
Click Open to confirm your selection and to close the Map Images dialog box.
Click OK to confirm your changes and to close the Properties Browser.
Bring the 2D Graphics window to the front.
Review the changes.

2D color elevation image Inlay

Lower elevations are darker in color and higher elevations are lighter in color. Mount St. Helens stands out as the highest point towards the bottom right of the inlaid image.

Converting a raw satellite image using the Imagery converter

Use the Imagery and Terrain Converter to convert a single, raw satellite image into a format that can be displayed in the 3D Graphics window. There are a number of valid imagery formats you can convert into a format supported by the STK application using the Imagery and Terrain Converter.

Opening the Single Image converter

The Single Image Converter creates image files compatible with the STK application from your source images and terrain.

Select the Utilities menu in the Menu Bar.
Select Imagery and Terrain Converter....
Select the Single Image page when the Imagery and Terrain Converter opens.

Selecting the image Input Data

The STK software comes preinstalled with a sample satellite image from the NASA ISS SERVIR Environmental Research and Visualization System (ISERV). ISERV was an automated system designed to acquire images of the Earth's surface from the International Space Station (ISS). ISERV data are provided as a true-color image in a 24-bit JPEG format . Select this image file to be converted.

Click the Image Filename ellipsis () in the Input Data panel.
Browse to the location of the ISERV imagery at <Install Dir>\Data\Resources\stktraining\imagery) when the File dialog box opens.
Select the ISERV_Imagery folder.
Click Open.
Select IPR201407092040194622N12217W.JPG.

This is a true color, 24-bit JPEG image. Each band is delivered as a grayscale, JPEG-compressed, 8-bit string of unsigned integers. You can also convert single-channel images (grayscale, for example) with the Imagery and Terrain Converter.

Click Open to confirm your selection and to close the File dialog box.

Unlike with some other image formats, such as the multiresolution seamless image database (MrSID) format, the ISERV JPEG image does not contain any embedded geospatial reference data. Instead, accompanying the JPEG image are a JGW "world" file and an auxiliary XML file that provide image location and georeferencing parameters. This is a common arrangement for raster files produced using geographic information system (GIS) software such as ArcGIS. ISERV images are georeferenced using the WGS84 Web Mercator (Auxiliary Sphere) coordinate system. The Imagery and Terrain Converter automatically reads the image extents from the metadata contained in these supporting files and into the Image fields located in the Image Extent panel. The STK application uses the Geospatial Data Abstraction Library (GDAL) to translate raster and geospatial data formats. GDAL supports certain well-known coordinate systems natively, including WGS84, WGS72, NAD83, NAD27, as well as any EPSG coordinate system.

Setting the image Output Data

Convert your raw satellite image into a JPEG 2000 image inlay.

Ensure the Use check box in the Terrain panel is cleared.

You will use the Terrain Region Converter to convert your terrain data to an inlay for this tutorial.

Ensure that JPEG 2000 Image (jp2) is selected for the Format in the Image File panel.
Click the Directory ellipsis () in the Image File panel.
Select the STK User folder in the left navigation pane when the Directory dialog box opens.
Select your scenario folder (for example, C:\Users\<username>\STK_ODTK 13\Imagery_Raw) in the folder and file list.
Click Select Folder to set the directory in which the converted images will be stored and to close the Directory dialog box.
Enter ISERV_StHelens in the Filename field.
Leave the JPEG 2000 Compression set to Lossless.

You want to maintain the full fidelity of the satellite image.

Click Convert.
Keep the Imagery and Terrain Converter open.

Creating a terrain inlay using the Terrain Region converter

Use the Terrain Region Converter to create terrain inlays (PDTT files) for a specific region. Creating terrain inlay files separately from inlaid imagery files (JPEG 2000 or PDTTX) enables you to convert an updated image for a particular region without having to reconvert the image data.

Select the Terrain Region page.
Open the Terrain Source drop-down list in the Input Data panel.
Select the path to the hoquiam-e.dem file in you scenario folder.
Click the Directory ellipsis () in the Output Data panel.
Select the STK User folder in the left navigation pane when the Directory dialog box opens.
Select your scenario folder (for example, C:\Users\<username>\STK_ODTK 13\Imagery_Raw) in the folder and file list.
Click Select Folder to set the directory in which the converted images will be stored and to close the Directory dialog box.
Enter StHelensTerrain in the Filename field.
Click Convert.
Click Close to close the Imagery and Terrain Converter when finished.

Displaying the imagery and terrain in the 3D Graphics window

Globe Manager allows to populate the central body of your 3D Graphics window with the following imagery, terrain, data sets, and tilesets. You can use Globe Manager to access imagery and terrain data items from local drives and external sources, such as Microsoft Bing™ Maps. You can organize imagery and terrain items into sets and turn on and off the display of individual imagery and terrain items or sets of items.

Opening the Globe Manager and turning off the default terrain imagery

In the Globe Manager window, you can use the Hierarchy tab to add central bodies, image items, terrain items, and terrain tile sets to a scenario. You can also organize image and terrain items into sets and change or delete the base images of globes in the scenario.

Bring the 3D Graphics window to the front.
Click Globe Manager () on the 3D Graphics window's Globe Manager toolbar.
Clear the check box for Aerial.ve () in the Globe Manager hierarchy if you have an Internet connection.

When you create a scenario while using the Internet, the STK application adds a Microsoft Bing™ Maps visualization to the Globe Manager hierarchy s a Virtual Earth (*.ve) file. There are several Bing™ Maps image options — Aerial, Hybrid, Roads, Roads Dark, and Roads Gray. By turning off Aerial.ve, you are simulating what you would see if you only had your DEM file and raw satellite imagery with which to work.

Adding the imagery and terrain to the Globe Manager hierarchy

Add the converted image and the terrain inlay to the 3D Graphics window by updating the Globe Manager hierarchy.

Select Earth () in the Globe Manager hierarchy.
Click Add Terrain/Imagery () on the Globe Manager Hierarchy toolbar.
Select Add Terrain/Imagery... () in the drop-down menu.
Open the Path drop-down list when the Globe Manager: Open Terrain and Imagery Data dialog box opens.
Select your scenario folder (for example, C:\Users\<username>\STK_ODTK 13\Imagery_Raw).
Select the check boxes for both ISERV_StHelens.jp2 and StHelensTerrain.pdtt.
Click Add.
Click No. when the Use Terrain for Analysis dialog box opens.

You are already using hoquiam-e.dem for analysis.

Viewing the terrain and imagery files in the 3D Graphics window

With your terrain and imagery inlaid, view them in the 3D Graphics window.

Right-click on ISERV_StHelens.jp2 () in the Globe Manager hierarchy.
Select Zoom To. () in the shortcut menu.
Use your mouse to view the image and surrounding terrain.

ISERV imagery and local terrain

You can clearly see the satellite image, which is draped on top of the terrain inlay. Terrain outside of the image extents is still visible.

Modeling a GPS tracking device

With your terrain configured, you can use it analytically. Start by modeling a GPS satellite tracking device.

Inserting a new Place object

Insert a Place object, which will simulate the GPS tracker.

Bring the Insert STK Objects tool () to the front.
Select Place () in the Select An Object To Be Inserted list.
Select Insert Default () in the Select a Method list.
Click Insert....
Right-click on Place1 () in the Object Browser.
Select Rename in the shortcut menu.
Rename Place1 () TrackingDevice.

Defining the Place object's position

Set the GPS tracker's coordinates to be within the extent of your analytical terrain.

Open TrackingDevice's () Properties ().
Select the Basic - Position page when the Properties Browser opens.
Set the following options in the Position panel:

Option	Value
Latitude	46.204 deg
Longitude	-122.188 deg
Height Above Ground	5 ft

Height Above Ground represents the height of the tracking device's antenna above the surface of the analytical terrain.

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

Defining the Place object's Azimuth-Elevation Mask

Define an azimuth-elevation mask for the GPS tracking device.

Select the Basic - AzElMask page.
Open the Use drop-down list.
Select Terrain Data.
Select the Use Mask for Access Constraint check box.
Click Apply to confirm your changes and to keep the Properties Browser open.

Selecting Terrain Data automatically creates and stores an azimuth-elevation (AzEl) mask file, which is an ASCII text file that is formatted for compatibility with the STK software and ends in an .aem extension, into your scenario folder. Turning on Use Mask for Access Constraint enables the Az-El Mask constraint, located on the Constraints - Basic page. Using the AzEl Mask constraint constrains access to the object by azimuth-elevation masking in a 360-degree field of view around the object being constrained.

Displaying the Azimuth-Elevation Mask

For situational awareness, you can display the Azimuth-Elevation Mask in both the 2D Graphics and 3D Graphics windows.

Select the 2D Graphics - AzElMask page.
Select the Show check box in the At Range panel.

This will display the terrain mask at a specified number of steps from a specified minimum to a specified maximum range.

Set the following options:

Option	Value
Number of Steps	10
Minimum Range	0 km
Maximum Range	50 km

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

Viewing the Azimuth Elevation Mask in the 3D Graphics window

Take a look at the tracking device's Az-El mask in the 3D Graphics window for situational awareness.

Bring the 3D Graphics window to the front.
Click Properties () on the 3D Window Defaults toolbar.
Select the Details page when the Properties Browser opens.
Select the Enable check box in the Label Declutter panel.
Click OK to confirm your selection and to close the Properties Browser.

Label Declutter is used to separate the labels on objects that are in close proximity for better identification in small areas. It also keeps object labels from being hidden by terrain.

Right-click on TrackingDevice () in the Object Browser.
Select Zoom To in the shortcut menu.
Using your mouse, zoom out until you can see the visual representation of the Azimuth-Elevation Mask.

azimuth elevation mask

Each ring represents a 10-kilometer range out to 50 kilometers. Around the edge of the view, you can see indications of North (N), South (S), East (E), and West (W). The view indicates that the view to the east, west, and south are poor. Visibility to the north, however, where the mountain's north face collapsed and was blow out in the eruption of 1980, is good.

Inserting the GPS constellation

You can insert the entire GPS constellation with one action by using the Load GPS Constellation method in accordance with your Propagator Defaults preferences. By default, if you have online operations enabled, it will use the OnlineAGI update mode to automatically insert the constellation at the time of your analysis period. When you are working in an environment without Internet connectivity, you can use external GPS Almanac files to load in a GPS constellation at an appropriate time period.

Loading the GPS constellation

Use the Load GPS Constellation method to insert the GPS constellation.

Bring the Insert STK Objects tool () to the front.
Insert a Satellite () object using the Load GPS Constellation () method.

Once loaded, you will see each individual Satellite () object and a Constellation () object containing all of the satellites. A Constellation object allows you to group objects together for use in other analysis tools in the STK application, such as Chains. In addition, the Constellation object allows for constraints and a routing file that determine the criteria as to how the Constellation is used in Chain computations.

Constraining the GPS constellation

Constellation constraints enable you to specify the criteria to be used when constellations are combined with other objects in a chain. Each pair of objects in the chain can be thought of as creating access pairs with a "from" object and a "to" object. Constellation constraints enable you to specify different logical and parent ownership constraints, depending on where the constellation sits in the chain, either as the "from" object or the "to" object. For the purposes of this tutorial, you require access to at least four GPS satellites at any given time. It doesn't matter which four. Also, you must take into account that, when calculating access, the access will be analyzed from the satellite to the GPS tracking device.

Open GPSConstellation's () Properties ().
Select the Constraints - Basic page when the Properties Browser opens.
Open the 'From' access position drop-down menu in the Logical Restriction panel.
Select At Least N.
Change the value to 4.

The constraint is satisfied if at least four satellites in the constellation meet the conditions for chain access.

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

Performing Chain analysis

A Chain object is a list of objects (either individual or grouped into constellations) in order of access. With the use of constellations, chains can be used to solve more sophisticated problems.

Inserting a new Chain object

Insert a new Chain object into your scenario.

Bring the Insert STK Objects tool () to the front.
Insert a Chain () object using the Insert Default () method.
Rename Chain1 () GPStoDevice.

Defining the start and end objects

The Chain object's Definition properties enable you to set up the Start and End objects and object connections used when computing access times from the Start to End objects. Objects in the Chain can be individual objects (Satellites, Sensors, Places, etc) or grouped objects (Constellations or Satellite Collections).

Open GPStoDevice's () Properties ().
Select the Basic - Definition page when the Properties Browser opens.
Click the Start Object ellipsis ().
Select GPSConstellation () when the Select Object dialog box opens.
Click OK to confirm your selection and to close the Select Object dialog box.
Click the End Object ellipsis ().
Select TrackingDevice () when the Select Object dialog box opens.
Click OK to confirm your selection and to close the Select Object dialog box.

Choosing the Chain object's connections

After you choose the start and end objects in your chain, you need to build the chain's connections.

Click Add in the Connections panel.
Click the From Object ellipsis ().
Select GPSConstellation () when the Select Object dialog box opens.
Click OK to confirm your selection and to close the Select Object dialog box.
Click the To Object ellipsis ().
Select TrackingDevice () when the Select Object dialog box.
Click OK to confirm your selection and to close the Select Object dialog box.
Click OK to confirm your changes and to close the Properties Browser.

Viewing the accesses in the 3D Graphics window

Animate the chain accesses in the 3D Graphics window.

Bring the 3D Graphics window to the front.
Zoom To TrackingDevice ().
Using your mouse, zoom out until you can see accesses from the ground site to the GPS satellites.

Chain accesses

Depending on the analysis period of your scenario, your view might be slightly different from the above image.

Click Start () in the Animation toolbar to animate the scenario.

Notice how the accesses don't appear until they're above the AzEl Mask. Conversely, they disappear when they reach the AzEl Mask. The terrain is being taken into account for the accesses.

Click Reset () in the Animation toolbar to reset the scenario when you are finished.

Generating a Complete Chain Access graph

A Complete Chain Access graph shows times during which access among all objects in a chain is possible through one or more strands.

Right-click on GPStoDevice () in the Object Browser.
Select Report & Graph Manager... () in the shortcut menu.
Clear the Show Reports check box in the Styles panel when the Report & Graph Manager opens.
Select the Complete Chain Access () graph style, located in the Installed Styles () folder in the Styles list.
Click Generate....
Review the Complete Chain Access graph.

Complete Chain Access graph

Your graph may look different than the one above. The Complete Chain Access graph is telling you exactly what you need to know. If there is a solid line across the report, that means you always have access to at least four or more GPS satellites during the entire analytical period. If there is a break in the line, that's a period when three or fewer GPS satellites are being accessed.

Close the Complete Chain Access graph.

Generating an Individual Strand Access graph

An Individual Strand Access graph represents one possible access pathway through the chain. For a chain that consists of a series of individual objects, only a single strand is possible. If a chain contains one or more constellations, multiple strands are possible, but constellation constraints (ANY OF, ALL OF, AT LEAST N, EXACTLY N) can affect the possible number of strands.

Return to the Report & Graph Manager.
Select the Individual Strand Access () graph style.
Click Generate....
Review the Individual Strand Access graph.

Individual Strand Access graph

Your graph will look different than the one above. The graph shows you when the ground site can see individual GPS satellites when there are at least four or more in view at the same time.

Keep the Individual Stand Access graph open.

Turning off the Azimuth Elevation Mask constraint

You can verify that analytical terrain is being used in your analysis by turning it off and reviewing the changes.

Open TrackingDevice's () Properties ().
Select the Constraints - Active page when the Properties Browser opens.
Clear the Enable check box for the Az-El Mask Constraint Name in the Active Constraints list.
Click Apply to confirm your change and to keep the Properties Browser open.

Refreshing the Individual Strand Access graph

Refresh the Individual Strand Access graph to see the changes.

Return to the Individual Strand Access graph.
Click Refresh (F5) () in the graph toolbar.

Updated Individual Strand Access graph

Your graph will look different than the one above. Notice that the individual strand accesses grow longer. This makes sense, as the surrounding terrain is no longer being accounted for in the analysis and the only active constraint is Line Of Sight.

Return to TrackingDevice's () Properties ().
Select the Enable check box for the Az-El Mask Constraint Name in the Active Constraints list.
Click OK to confirm your selection and to close the Properties Browser.
Return to the Individual Strand Access graph.
Click Refresh (F5) () on the graph's toolbar.

The individual strands shrink because analytical terrain is again being used in the analysis.

Saving your work

Clean up your workspace and save your scenario.

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

Summary

You began by loading a USGS DEM terrain file into your scenario which you used as analytical terrain. You used the Create Color Elevation Imagery tool to create an image from the terrain data that showed elevation data colored by height in the 2D Graphics window. You used the Imagery and Terrain Converter's Single Image Converter utility to convert an ISERV image, which you displayed in the 3D Graphics window, and the Terrain Converter to create a pdtt terrain inlay file from the USGS DEM file. You used this file to visualize the terrain features in the 3D Graphics window. You inserted a Place object into the scenario that simulated a GPS tracking device. You set up the tracking device to use the terrain analytically. You propagated GPS Satellites from GPS almanac and created a Constellation object which contained the GPS Satellites. Finally, you inserted a Chain object into the scenario and created accesses from the GPS Constellation to the tracking device. You required at least four or more satellites in your analysis which you graphed using a Complete Chain Access graph and an Individual Strand Access graph.

On you own

Should you use AzEl Mask or Terrain Mask? Make sure to read the pros and cons between the two. When using a Facility, Place or Target object in an access computation, obscuration of the line of sight by terrain can be accounted for in one of two ways: selection of a Terrain Mask constraint or selection of an AzEl Mask constraint. While both constraints serve to model the same physical obstruction, there are important differences between the constraints, which should be considered when selecting between the two. Try using a Terrain Mask instead of an Az-El Mask as a constraint and compare the differences in your reports or graphs and the difference in calculation time.

Also, you could enable Terrain Server and enable either Line-Of-Sight Terrain Mask or Azimuth/Elevation Mask. Place a ground site anywhere on the globe and access a satellite of your choice. Make sure to tell the ground site to use terrain. Try accessing a Ground Vehicle object or an Aircraft object as it moves through terrain.

Further study

For additional information on how to use the Imagery and Terrain Converter utility analytically with Chain and Constellation objects, see the following tutorial:

Using Terrain, Chains, and Constellations

For a more in-depth look at the process and workflows of the Create Color Elevation Imagery utility and Imagery and Terrain Converter, see the following tutorial:

Using External Terrain Data