AutoCAD Civil 3D General Discussion

AutoCAD Civil 3D General Discussion

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Post 1 of 8

Unwanted rounding of elevation values when exporting TIN surface to DEM

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07-07-2010 12:14 PM

My workflow consists of building a point cloud object from a LAS file, filtering it for ground data, and and building a surface object with it. Breaklines are inserted into a surface object, and then the surface object is exported to a DEM file to be used in a GIS application. The problem is that Civil 3D rounds the elevations to 1-foot intervals, even when the file is structurally floating point. Does anyone know how to override this rounding to get floating point values that reflects the original data?

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Post 2 of 8

Re: Unwanted rounding of elevation values when exporting TIN surface to DEM

07-08-2010 01:56 PM in reply to: jblix

jblix,

 

How do you mean C3D rounds elevations?  Are you referring to the points in the surface or the labels?

 

A sample file would help, too.

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Re: Unwanted rounding of elevation values when exporting TIN surface to DEM

07-08-2010 02:10 PM in reply to: jblix

I'm referring to the elevation point value. When the values are forced into descrete 1-ft increments, I can't get the benefit of a GIS hydro flow analysis that comes with the continuousness of floating point values. Instead of a steady curve of the surface, you have a series of stair steps.

 

Autodesk has informed me that the integer output is by design, for whatever reason. I'm using C3d 2011, by the way.

 

I seem to have encountered the big void that exists between CAD and GIS data types, and I'll probably end up purchasing some kind of ETL package such as Safe Software to do what I need to do.

 

I would enclose an attatchment, but the file is kinda huge.

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Post 4 of 8

Re: Unwanted rounding of elevation values when exporting TIN surface to DEM

07-08-2010 02:47 PM in reply to: jblix

What do you mean by "elevation point value"?  I'm not aware of any elevations in C3D that are forced to discreet 1-foot intervals.

 

Are you talking about something in the drawing?  Or the resulting text file when you try to output a DEM using Civil 3D?  Or something else?

Sinc
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Post 5 of 8

Re: Unwanted rounding of elevation values when exporting TIN surface to DEM

07-08-2010 11:21 PM in reply to: Sinc

Output a surface to a DEM, it rounds to the nearest drawing unit. I've tested in 2010 using US feet, and the resulting DEM is only output to the nearest foot. But then, it's my understanding that DEM's are mainly for very large areas (USGS Quad) so the 'nearest unit' makes sense for that case. For the typical C3D job, though, a bit more accuracy is usually warranted.

Jeff_M, also a frequent Swamper
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Post 6 of 8

Re: Unwanted rounding of elevation values when exporting TIN surface to DEM

07-09-2010 06:01 AM in reply to: jblix

With the surface precision of the Civil 3d surface, why not perform the hydro analysis in Civil 3d?

 

Map is able to generate a surface from the point cloud as well.

Matthew Anderson, PE
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Post 7 of 8

Re: Unwanted rounding of elevation values when exporting TIN surface to DEM

07-09-2010 06:07 AM in reply to: jblix

That's my next line of inquiry, actually. I'm a newbie to C3D, so I'm still exploring the possibilities. Nevertheless, I would like to be able to open things up between our CAD and GIS software.

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Post 8 of 8

Re: Unwanted rounding of elevation values when exporting TIN surface to DEM

12-31-2012 01:28 PM in reply to: jblix

When I bring in an asc Lidar file into a point cloud the elevations are rounded to the nearest meter.  If I change the asc file to a txt file, I can see that the elevations are accurate to the millimeter.  Any suggestions?

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