Terrain

The Terrain properties page of a scenario can be used 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.

Select Use terrain server for analysis 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 preferences window within the Application preferences window.

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

Information about the currently connected terrain server, including the version of terrain server API that it is using, is displayed to the right of the analysis operations options.

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.

Local terrain data can be specified 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 terrain on the Earth to determine if your ground facility is obscured by mountains. Select a body from the Central Body drop-down list 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)	PDTT Version 1 or Version 2 STK Terrain files. Version 2 .pdtt files support sub-meter terrain and are not compatible with versions of STK previous to version 10.
STK World Terrain (HDR)	DEM-derived data for the entire Earth. When loading, select a header file.
ArcInfo Binary Grid (adf)	ArcInfo Binary Grid format, using WGS84 as a vertical datum.
ArcInfo Binary Grid - MSL Vertical Datum (adf)	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 Web site.
ArcInfo Grid Depth MSL	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)	Mars Orbiter Laser Altimeter terrain data.
MUSE Raster File (DTE) >	NGA (formerly known as NIMA) elevation data that has been converted using the MUSE software raster importer. MUSE terrain files contain position information.
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)	NGA (formerly known as NIMA) Digital Terrain Elevation Data (DTED). When loading, select a header file.
Tagged Image File Format (TIF)	TIF format containing elevation data referenced to the WGS84 ellipsoid.
Tagged Image File Format - MSL (TIF)	TIF format containing elevation data referenced to Mean Sea Level.
USGS Digital Elevation Model (DEM) >	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.

Using Terrain for Analysis

You can include terrain elevation data in the computation of:

• The position of a facility, place or target. Go to the Position page for either a facility, place or target and select Use terrain data. This capability is enabled by default.
  • The Height Above Ground value for a facility, place or target. If you have selected to use terrain data for the object's position, then the height above ground defined for the object will be applied 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 appropriate object and select Terrain from the Altitude Reference drop-down menu. For ground vehicles, this capability is enabled by default.
• Centroid altitude for an area target. Go to the Centroid page for the area target and select Use terrain data for altitude update. This capability is enabled by default.
• An azimuth-elevation mask. Go to the AzElMask page for either a facility, place or target and select Terrain Data from the Use drop-down menu.
• Boundary wall for an area target or line target. Go to the 3D Graphics Attributes page for the area target or line target and select Height from Terrain for the Upper Edge and Lower Edge of the Boundary Wall.

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.

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