NAME: Directional Slopes, v. 1.2a (Click Name to Download)
View Online PDF Manual Here:
Last modified: October 6, 2006
TOPICS: Slope Direction Angle Bearing
DESCRIPTION: This extension generates a grid of estimated slope values, where the slope is measured in specified directions. This differs from the standard slope value which estimates the absolute slope in the steepest direction.
RESULTS: Produces a grid of slope values in either Percent or Degrees.
REQUIRES: Spatial Analyst, plus a projected grid of elevation values. The elevation units must be the same as the coordinate system units. If your elevation grid is unprojected and you do not have access to ArcInfo Grid Projection utilities, you can use the author’s Grid Projector extension to project your grid (see http://www.jennessent.com/arcview/grid_theme_projector.htm).
This extension also requires that the file "avdlog.dll" be present in the ArcView/BIN32 directory (or $AVBIN/avdlog.dll) and that the Dialog Designer extension be located in your ArcView/ext32 directory, which they usually are if you're running AV 3.1 or better. The Dialog Designer doesn't have to be loaded; it just has to be available. If you are running AV 3.0a, you can download the appropriate files for free from ESRI at:
REVISIONS: Version 1.2a: Minor update, adds a function to check scripts if extension crashes.
Recommended Citation Format: For those who wish to cite this extension, the author recommends something similar to:
Jenness, J. 2006. Directional Slope (dir_slope.avx) extension for ArcView 3.x, v. 1.2a. Jenness Enterprises. Available at: http://www.jennessent.com/arcview/dir_slopes.htm.
Please let me know if you cite this extension in a publication (firstname.lastname@example.org). I will update the citation list to include any publications that I am told about.
Begin by placing the "dir_slope.avx" file into the ArcView extensions directory (../../Av_gis30/Arcview/ext32/).
After starting ArcView, load the extension by clicking on File --> Extensions… , scrolling down through the list of available extensions, and then clicking on the checkbox next to the extension called "Directional Slope."
The extension will add two buttons to your View. These buttons will only be enabled if you have a single grid theme active in your view. The slope calculations will be done on the active grid, and the extension assumes this is a grid of elevation values in which the elevation units are the same as the X- and Y-Coordinate units (i.e. the grid must be projected).
For complete instructions, plus an explanation of the concepts and algorithms involved, please refer to the attached manual or view the online manual here:
IMPORTANT: There are many ways to calculate slope based on different assumptions of what the slope should represent. The method presented here makes intuitive sense to the author, but please review the methods section (How this extension calculates slope, p. 7), to judge for yourself whether this method is appropriate for your analysis.
Enjoy! Please contact the author if you have problems or find bugs.
Please visit Jenness Enterprises ArcView Extensions site for more ArcView Extensions and other software by the author. We also offer customized ArcView-based GIS consultation services to help you meet your specific data analysis and application development needs.