slope surface percentages

[Anonymous]

I am using AutoCAD Civil 3D to do a slope analysis across project locations. When defining slope categories, I am finding that the max slope percentages are astronomically high; ranges are being returned up to 360,000%--and I've only done three regions! I understand vertical slope but these percentages are not realistic by any means, especially through the areas in which I am working.

A specific example: between a contour at elevation of 792 ft and a contour at elevation of 794 ft at a distance of approximately 60 feet, the slope percentage being returned is in the 9000% range. There is not a sudden drop or rapid change in elevation between these two contour intervals to provide reason for this high of a percentage. I would expect to have a slope percentage nearer the 3% range.

The data source of the contour information is LiDAR being brought into CAD via the task-based geospatial option using MapImport. All data tables are being kept. Polygons are being imported as closed polygons. There are no surface errors being reported upon creation. The project locations were created in another program and imported into CAD using the same manner.

Insight? The only thing that I can conjure up is that there is some sort setting issue.

In responding, please provide step-by-step instructions on how to resolve this issue as I am not fluent in CADspeak.

Thanks!

[tcorey]

If this is LIDAR data, then don't be surprised when a seemingly even slope has slope percentage values in the thousands. Lidar will pick up rocks and debris that a surveyor would not.

If you set your own ranges, Civil 3D will ignore the nearly vertical faces. You don't have to use the 9000% value if you know it's unrealistic.

[troma]

You could try setting a colour in the analysis for the 9000% range, or whatever. Then look around in the drawing to find it. It's probably a tiny sliver somewhere. You can probably ignore it as Tim says, but sometimes I like to know what & where something is first.

[coolblues]

how would you know your maximum slope percentage then? im having same issue as the OP. even if I already cheked my data im still having a very high value for my max slope.

[troma]

I guess you wouldn't.
Will a slope analysis help you?