Elevation Contour Data

• often, there is no regular elevation grid available - only a set of contour lines
• the USGS provides elevation contour lines in DLG format
  • it calls them "hypsography vector data"
  • fortunately, they also provide the DEM, making their contours unnecessary
• a common format for storing contours is ESRI Shape files
• if you're starting with paper topographical maps, you will need to scan it and extract the contours
  • use a package such as R2V ($1500) to produce the contour vectors
  • are there lower-cost options as well, such as shareware programs?

Converting from irregular points or contour maps to an elevation grid

• R2V itself reportedly provides this functionality, but there are numerous less expensive options
• Terrainmap.com article: Extracting DEMs from Topographic Maps shows how to use the R2V demo
  • now, on the same Terrainmap.com website, you can download BLACKART, a free contour interpolation program which reportedly implements some very powerful algorithms and produces impressive output
  • however, it is still quite rough and requires considerable learning and experimentation to use
  • read some of the background material on the problem and solutions
• Global Mapper ($250)
  • the user-friendly swiss-army-knife of GIS can also convert contour to grid
  • reportedly the process is:
    • Load a shapefile
    • Export it out to an .xyz ASCII text file (make sure you export the elevations and feature attributes too).
    • Open the ASCII text file using “open generic ASCII text file”
    • Choose “create elevation grid from point data”
    • This should generate a grid that you can then export to .dem, .txt, or other common formats.
• 3DField (shareware, $50)
  • small utility for Win32 which can convert points to contours, and contours to grids
  • grids can be saved in .GRD (Surfer Grid format) which can be read in VTBuilder (i tested this, and it works)
  • also claims to automate digitization of contours from scanned contour maps (i did not test this)
• Surfer ($600 from Golden Software)
  • it will convert a set of points to a grid, and a grid to contours, but will it convert contours to a grid?  Golden says:
  • "Surfer can help you convert the contours to XYZ data with onscreen digitizing. Load the SHP file with the contours as a base map, select the map, then choose the Map | Digitize menu. The XY coordinates are displayed in the status bar (at the bottom of the Surfer window), and clicking on screen stores the XY coordinates in the digit.bln edit window. The Z value is not stored automatically, but you can add the Z value in the Surfer worksheet.
    Once you have an XYZ data file for your contours, choose the Grid | Data menu command to interpolate a grid file from the XYZ data."
  • you can save from Surfer in their Grid format (.GRD) which can be read in VTBuilder
• ANUDEM (~$300 academic, ~$1000 commercial)
  • Australian research project that became a product
  • runs on Unix (command-line) and Windows (with GUI)
  • converts points, contours, stream lines, and lake boundaries into grids
  • makes full use of the hydrology info for much better accuracy
  • reads: raw ASCII and standard ArcInfo and IDRISI vector formats
  • writes: ArcInfo and IDRISI ASCII and binary grid formats
• surfit (free, open source)
  • calculate regular grid from various data (scattered points, curves, surfaces, etc), which includes contours
  • installer for Windows, RPMs for Linux
• SurGe (shareware, Windows only)
  • interpolates points, contours and breaklines to a grid
  • pro: appears to be quite powerful and flexible in different styles of interpolation, can output to Arc Ascii Grid
  • con: only reads data in its own ad-hoc text format, does not deal with coordinate systems, UI is quite dated
• GRASS (freeware)
  • can reportedly convert contour vectors to a DEM
  • learning curve is substantial, but no worse than a high-end commercial package (e.g. ArcInfo)
• ERDAS Imagine (high-end, expensive)
  • reportedly, "The IMAGINE 3D-Surfacing tool could translate a non-regular grid to height-field image. Grid points could be from point/line ARC Coverage data (or from many sources via ERDAS import tool) or from text file."
• ESRI ArcInfo (high-end, expensive)
  • for people that already own ArcInfo, the TOPOGRID command in the Grid module will convert contours to grids
  • reportedly, ESRI actually licensed the ANUDEM (see above) source code, so TOPOGRID is basically a slightly out of date version of ANUDEM
• Autodesk Product Line (expensive)
  • the mid-range product Autodesk Map won't generate Grids from Points, but their product Autodesk Land Desktop will
• other possible tools:
  • SPRING (free Brazilian GIS/imagery package, large, looks like a long learning curve)
  • Perspective Edge QuikGrid (shareware, $37 for full version)
  • Softree Terrain Tools ($280 for version which does contouring and DTM)
  • Safe Software FME (Professional Suite, $2000)
  • MFWorks ($?) is a raster GIS which will convert contour data to a DEM