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Elevation Layers

VTBuilder will read in elevation files from a large number of formats, and process them to prepare for visualization. You can load multiple files, select the area of interest to export, resample them, and many other operations.

VTBuilder can import elevation grid data from these formats:

• USGS DEM (Digital Elevation Models)
• SDTS DEM
• MicroDEM DEM
• several less-common flavors of DEM
• GTOPO30
• DTED0 (DTED1 is untested)
• CDF/netCDF
• image formats: PNG, TIF, GeoTIFF
• PGM ("portable graymap format")
• Surfer 7 Binary Grid
• TerraGen terrains
• raw data without a header
• ArcInfo Ascii Grid
• ArcInfo BIL (includes NOAA Globe files)
• several other formats

If any of your terrain grids use different coordinates (such as different UTM zones), VTBuilder can convert them to the same projection for you.

The native format for elevation grids is the BT format.  BT can be read by the VTP Enviro program and other virtual terrain software.

VTBuilder can also export elevation to ArcInfo ASCII Grid, GeoTIFF, TerraGen, BMP, STM, MSI Planet, VRML ElevationGrid, RAW/INF for MS Flight Simulator, ChunkLOD, and 16-bit PNG.  However, format conversion is not the intended use of the software.  The primary purpose of VTBuilder is to prepare data for 3D visualization.

TINs (Triangular Irregular Networks)

Additionally, VTBuilder can import TIN elevation from these formats:

• AutoCAD DXF

The native format for TIN data is the ITF file format.  ITF can be read by the VTP Enviro program for visualization.  Unfortunately, there is no common standard file format for TIN data.  That is why we had to invent our own ad-hoc native format (ITF).

Display of Elevation Layers

The default is to display elevation as artificially shaded and false-colored by elevation.  Elevation at sea level is shown in blue.  Areas of unknown elevation are shown in red, unless hidden with the View: Hide Unknown Areas option

How To Sample and Export Elevation

• Use the Area Tool to drag the black lines with the mouse to indicate the area of interest.  You can also type in precise extents with the command Area Tool - Numeric Values
• Use the command "Area Tool - Sample Elevation" to create a BT file.  There will also be a PRJ file created with the same name as the BT file, which contains a full description of the projection. For example:

  hawaii_1k.bt

  hawaii_1k.prj

• Important!  If you will be using this for terrain LOD in Enviro (recommended), let VTBuilder enforce the size constraints in the Sample Elevation dialog.
• If you have overlapping elevation layers, then the last elevation (in the order shown in the Layers View) with valid data will override the others.  Therefore, if you have overlapping low-resolution and high-resolution layers, and want to sample them together, load the low-resolution layers first.

Elevation Menu

• Select Elevation Layer
  • Use this mode to pick elevation layers with the mouse.
• Scale Elevation
  • For the currently selected layer, scales the elevation values up or down.
• Remove Elevation Range...
  • For the currently selected layer, asks the user for a range of elevation, for example -100 to 100 meters, then sets all elevation points which are within this range to 'unknown' (shown as red)
• Fill In Unknown Areas
  • For the currently selected layer, this feature can be used to fill "cracks" of unknown values.  The unknown areas are filled in by interpolating the surrounding known areas.
• Set Unknown Areas
  • For the currently selected layer, sets all unknown areas to the value you provide.
• Export To...
  • Writes the current elevation grid layer to one of the following file formats:
    • ArcInfo ASCII Grid
    • GeoTIFF
    • TerraGen
    • BMP (scaled to 8-bit)
    • STM
    • MSI Planet
    • VRML ElevationGrid
    • RAW/INF (for Microsoft Flight Simulator)
    • ChunkLOD (.chu)
    • PNG (16-bit greyscale)
    • 3TX
• Export to Tiles...
  • Writes the current elevation grid layer to a set of tiles.  The Tiling Options dialog will be shown.  The output file should be an .ini file on your data path.  For example, if you save to /Data/Elevation/Foo.ini, then that file will contain a description of the tileset, and all the tiles will be placed in a directory called /Data/Elevation/Foo
• Render to Bitmap...
  • Creates and a rendered bitmap (GeoTIFF or JPEG) of the currently selected Elevation Layer.  The elevation is used to provide artificial color and shading for the bitmap.  The bitmap can either be written to disk, or created a new Image Layer.  When you don't have any imagery for your area, only elevation, this can give you a visually useful image - similar to the "Texture: Derive from Elevation" option in Enviro, but better because the image is generated before runtime.