Tuesday, July 26, 2011

Average Slope By Contour Lengths

I’m not quite sure why, but planners tend to come up with interesting ways to calculate the average slope of a site. It seems like using triangles would be best, but sometimes they want to use contours. Unfortunately Civil 3D doesn’t have a way to calculate the Average Slope of a surface based on contour lengths.image
So to fix this deficiency I’ve created a report to perform the calculation for you. The report utilizes the formula in the above picture. The report is installed into the Toolbox, and the user executes the Average Slope Calculation. After selecting a surface the user is prompted to select a point to place an AutoCAD table. The table can then be exported to a csv file if needed in another format. The precision of the numbers is taken from the settings of the drawing.
Contour – Surface Commands Settings > Add Contour Labeling Settings > Elevation
Area – Surface Feature Settings > Area
Grade – Surface Feature Settings > Grade/Slope
Here is the report in action.
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The report is now available on the Autodesk App Store


KLM said...

But this confuses me because what if you have an incredibly flat 900 SF site that has two 1' contours that just wind all throughout the site for a total of 450 LF. This would result in an average slope of 0.5; the same as a site with 15' of vertical change across the 30' length.

Christopher Fugitt said...

I think I mentioned using triangle slope would be a better method of calculating average slope.


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