Terrain

You can use the Terrain properties page of a scenario to enable streaming terrain and associated analytical operations and to define a list of locally available terrain files to be used by the scenario.

In addition to describing the functions of the Terrain properties page, this topic also provides an overview of the uses of terrain data for analysis and visualization in STK. See Using Terrain Data.

Streaming terrain from a Terrain Server

A terrain server distributes Earth terrain data for analysis and visualization. By default, STK connects to the AGI Terrain Server, which is available via an internet connection to all STK users. You can customize these settings.

In the scenario properties, on the Basic > Terrain page, select the Use terrain server for analysis check box to stream terrain data from the server and tileset that you are currently connected to. To configure your connection to a terrain server, click Edit Preferences..., which will open the Terrain Services dialog box within the Data Services window.

The Basic >Terrain page also displays the currently connected terrain server and tileset.

Terrain data files

The Custom Analysis Terrain Sources table can be used to specify locally available terrain data files to be used for analysis and visualization in the scenario in addition to, or instead of, streaming terrain data from a terrain server. If a scenario has access to local and streaming terrain data for the same region, it will use the local data for analysis and visualization.

You can specify local terrain data for Earth, the Moon, and the traditional planets of the solar system. For example, in the same scenario, you can put terrain on the Moon to see how a rover on the Moon is obscured by lunar craters and at the same time put terrain on the Earth to determine if your ground facility is obscured by mountains. Select a body from the Central Body shortcut menu to display the terrain data files currently specified for it in the scenario and to add or remove files for use.

For each terrain file, the Terrain properties page displays:

• Location of the terrain file
• Whether the terrain source is used in this scenario
• Latitude and longitude values for the four corners of the image

Click Add to import one or more terrain data files, and Remove or Remove All to delete individual or all terrain data files for the selected central body from the scenario.

Custom analysis terrain sources

You can import the following files into STK for visualization and analysis:

Terrain Type Name	Description
STK Terrain File (pdtt)	These are PDTT Version 1 or Version 2 STK Terrain files. Version 2 .pdtt files support submeter terrain and are not compatible with versions of STK previous to version 10.
STK World Terrain (HDR)	Contains DEM-derived data for the entire Earth. When loading, select a header file.
ArcInfo Binary Grid (adf)	Data is in the ArcInfo Binary Grid format, using WGS84 as a vertical datum.
ArcInfo Binary Grid - MSL Vertical Datum (adf)	Data is in the ArcInfo Binary Grid format, using MSL as a vertical datum. This is appropriate for NED terrain data, in the ADF format, which is available from the USGS website.
ArcInfo Grid Depth MSL	Data is in the ArcInfo Grid format, using depths relative to MSL.
GEODAS Grid Data (g98)	GEODAS (GEOphysical DAta System) is an interactive database management system developed by the National Geophysical Data Center (NGDC) for use in the assimilation, storage, and retrieval of geophysical data.
GTOPO30 DEM (hdr)	GTOPO30 is a global digital elevation model (DEM) with a horizontal grid spacing of 30 arc seconds (approximately 1 kilometer).
MOLA Terrain (LBL)	This is Mars Orbiter Laser Altimeter terrain data.
MUSE Raster File (DTE) >	This is NGA (formerly known as NIMA) elevation data that has been converted using the MUSE software raster importer. MUSE terrain files contain position information. The MUSE Raster file format is deprecated for STK 12.8.
NIMA/NGA DTED Level 0 (DT0)	NIMA/NGA DTED Level 0
NIMA/NGA DTED Level 1 (DT1)	NIMA/NGA DTED Level 1
NIMA/NGA DTED Level 2 (DT2)	NIMA/NGA DTED Level 2
NIMA/NGA DTED Level 3 (DT3)	NIMA/NGA DTED Level 3
NIMA/NGA DTED Level 4 (DT4)	NIMA/NGA DTED Level 4
NIMA/NGA DTED Level 5 (DT5)	NIMA/NGA DTED Level 5
NIMA/NGA Terrain Directory (DMED)	This is NGA (formerly known as NIMA) Digital Terrain Elevation Data (DTED). When loading, select a header file.
Tagged Image File Format (TIF)	Data is in the TIF format containing elevation data referenced to the WGS84 ellipsoid.
Tagged Image File Format - MSL (TIF)	Data is in the TIF format containing elevation data referenced to Mean Sea Level.
USGS Digital Elevation Model (DEM) >	This is U.S. Geological Survey data. Moderate resolution.

The use of topography data for bodies other than the Earth may require modifications to the reference shape of the body for accurate determination of the body surface. For more information, see Using Topography Data for Central Bodies Other than the Earth.

Using terrain data

You can use terrain data for analysis and visualization with many STK Objects.

Combining terrain sources

When you enable the terrain server for analysis and also enable one or more terrain data files for Earth, STK addresses requests for terrain height by first checking against the set of terrain files. If the terrain data files cannot provide the terrain height for the requested location(s), STK then makes requests to terrain server. This behavior is particularly useful when only a small region needs high resolution terrain data. You can specify that data using a local terrain file without uploading it to the terrain server. When outside the region, STK uses the terrain server heights.

Combining terrain sources does not apply when creating an AzEl Mask. If you select the terrain server for analysis and the Azimuth/Elevation Mask option in the Advanced Analysis Operations field, STK will compute the mask entirely on the terrain server and will not use local terrain files. If you do not select the terrain server, STK computes the AzEl Mask using local terrain files only.

Using a terrain server for analysis

A terrain server can perform some common terrain analysis operations. Select the Line-Of-Sight Terrain Mask and Azimuth/Elevation Mask check boxes to use the connected terrain server to perform these operations when your scenario requires them.

For vehicles with the Astrogator, Spice, DIS, or Spline propagator, STK will not compute access for them when you select the Line-of-Sight Terrain Mask option.

You can include terrain elevation data in the computation of:

• The position of a facility, place, or target. Go to the Position page for a facility, place, or target and select the Use terrain data check box. This capability is selected by default.
  • The Height Above Ground value for a facility, place, or target. If you selected to use terrain data for the object's position, then STK will apply the Height Above Ground value for the object to the altitude given by the terrain data at its position.
• The altitude reference for an aircraft, ground vehicle, or ship. Go to the Route page for the object and select Terrain from the Altitude Reference shortcut menu. For ground vehicles, this capability is selected by default.
• Centroid altitude for an area target. Go to the Centroid page for the area target and select the Use terrain data for altitude update check box. This capability is selected by default.
• An azimuth-elevation mask. Go to the AzElMask page for a facility, place, or target and select Terrain Data from the Use shortcut menu.
• Boundary wall for an area target or line target. Go to the 3D Graphics Attributes page for the area target or line target. First select the Show Boundary Wall check box. Then select Height from Terrain for the Upper Edge and Lower Edge of the Boundary Wall.

Analysis results from using data from the terrain server are different than results using local terrain, even when the terrain server is using the same base data as in the local terrain file. One reason is that the terrain server holds data using a quantized mesh format, which is efficient for visualization but differs from the local terrain format. Another reason is that the terrain server interpolates its data using triangles, whereas local terrain interpolation uses squares. So if, for example, you use STK to generate accesses for a satellite and a mountaintop facility, the resulting access intervals when using a terrain server could be seconds different than when using local terrain.

Using terrain for visualization

If you are streaming terrain data from a terrain server, it is automatically available for visualization in the 3D Graphics window. If you are using local terrain files, you will need to convert them to PDTT format using either the Terrain Converter or the Terrain Region Converter.

When displaying individual terrain tiles in the 3D Graphics window, the edges of the terrain that are above the WGS84 ellipsoid have walls that drop down to the ellipsoid. The bottom of the walls may not exactly match the neighboring terrain or the ellipsoid, so you may see cracks in the central body surface.