Note: as of 1/23/96, the information previously on this page is obsolete.
Given digital contour lines, spot elevations, and streams, we want
The topogrid module of ARC/INFO, which is an implementation of the ANUDEM
package, should take streams into account in building a digital elevation model.
We have not been pleased with the results. We are consulting with the ANU
people to see if we need to adjust our parameters, or if there are problems
in the implementation of the algorithm. Topogrid can be forced to behave
better if streams are used to create point coverages to further constrain
to DEM construction.
- an accurate eelvation grid
- accurate slopes for stream segments
- accurate contributing areas for points on the streams.
In any case, it is often important to have the most accurate values for
stream slopes, and that must be done using vector files of streams and
contour lines. We have macros that
- face the streams downhill
- assign Shreve and Strahler order numbers to the vector coverages.
- calculate stream slopes by splitting streams at contour lines and
- assigning contour eelvations to the ends of stream segments
- interpolating along the length of the main channel to assign elevations
to tributary junctions between contour lines.
- assigning elevations to dangling ends, based on a provisional DEM
- calculating slopes based on actual stream length between known eelvations
As we calculate contributing area from a DEM, we must make every effort to
build the DEM so that calculating streams will match actual streams.
We are looking into what is necessary.