Derivative Grids

Derivative Grids

Invokes popup menu, which can be selected in two places:

Calculate Menu, Derivative Grid
Raster GIS menu, Create derivative grid

This will create a new grid, with the same size and spacing as the original grid.

You must save the new grids (File, Save DEM) if you want to use them again. When you save, you can choose either the MICRODEM or GeoTIFF format. The derivative grid can be manipulated in its own right.'

The program can automatically save the files if your pick the Multiple parameters option, which will be savbed to a subdirectory "geomorph_grids" in the directory with the original DEM. If you want to convert to GeoTiff, either:

Open and then File, Save DEM, and pick Geotiff.
Data Manipulation, Resample, DEM format, convert to Geotiff, which allows conversion of all DEMs in a directory.

Some options (relief, openness) require that a region size be selected. The size is in meters, and converted into the number of grid points needed. The computations will use a square centered on the point.

Some options (e.g. slope, reflectance, aspect) can be selected from the display option of the DEM display, but have limited modification capability since they are just display modes of the DEM.

Multiple parameters--This allows creation of multiple grids while you do something else. Parameters within each grouping are computed together, and doing more than adds little time, but will increase memory usage.
Slope--uses current slope algorithm
- Percent (100 * tan)
- Degrees
- Sin
- log10 tangent
- ln tangent
- sqrt sine
Aspect
Curvature: create 5 different curvature grids, or all five at once. They will be drawn with a percentile color stretch. The five at once will be threaded and probably execute faster than a single layer.
Relief
- Relief, average elevation, elevation standard deviation, REL (percentage of area that is lower), and TPI: all for a specified region size
- Relief, Summit levels, Base Level, Geophysical Relief
- Immediate neighborhood drop: drop off is the distance from the point to the lowest point in the box with the selected size.
Rugosity
Convergence index
Topographic ruggedness index
Openness
Reflectance
Terrain category: pick a terrain category, and the points meeting the criteria will have a single value in the resulting grid.
Transform elevations
- Meter elevations
- Ln (natural log)
- Log (base 10) transform elevations
- Normalize parameter
- Parameter percentiles
Terrain classification--uses current classification algorithm
- Ridges--all peaks and ridges will have the elevation; other points will be missing
- Valleys--all streams will have the elevation; other points will be missing
- All terrain categories--will have an integer code for the category
Iwashashi and Pike Classification
Terrain organization maps: Organization (s2/s3), Flatness (s1s2, inverse slope), Fabric direction, Roughness factor (slope)
Moments for region (elevation, slope, two curvatures, the moments for a selected region size)
Point density: divides value at each grid point by size of the grid; the result will in count/m².
Optimal viewshed location
Vegetation obstacle grid. Will have the same size and spacing as the DEM. Done from:
- NLCD 2001
- Shapefile
- NBCD
- Landfire
NLCD grid--NLCD 2001 categories
NLCD grid--NLCD-1992
Landfire grid

Last revision 6/8/2019