Author Topic: Civil3D Surface Contours not matching MAP Contours from GeoTiff  (Read 830 times)

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MSTG007

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Civil3D Surface Contours not matching MAP Contours from GeoTiff
« on: September 21, 2018, 02:59:07 PM »
I am trying to figure out why I cannot get the contours to match from Civil3D Surface Contours to a MAP Contours. The RED contours are from MAP and the Yellow and Cyan are from Civil3D. I used the same geotiff and the coordinate system is US feet not international foot.

From Civil3D Surface \ Create Surface from DEM and selected the Geotiff.

I turned on _Mapwspace. Data Button \ Connect to Data \ Add Raster Image or Surface Contour and browsed to the GeoTiff \ Then Connect Button \ Add to Map Button.

In the Task Pane, I Selected on the top Layer (Green and Dark Green) / Right Click / Create Contour Layer / Set Contour interval to 1 and 5 feet / Give the file a name to save / Finally the OK Button.

Am I doing something wrong or do I just need to stick with Civil3D over MAP in creating contours?

Thanks for any help. Just trying to understand why it does what it does. lol
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BuckoAk

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Re: Civil3D Surface Contours not matching MAP Contours from GeoTiff
« Reply #1 on: September 21, 2018, 04:41:29 PM »
The GeoTiffs we have received in the past were in meters and so had to be converted to feet.  Do you know if your GeoTiff is in meters or feet?

MSTG007

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Re: Civil3D Surface Contours not matching MAP Contours from GeoTiff
« Reply #2 on: September 21, 2018, 04:57:17 PM »
Itís in feet... they flew it and had it in a LAS. Then gave us the Geotiff
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mjfarrell

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Re: Civil3D Surface Contours not matching MAP Contours from GeoTiff
« Reply #3 on: September 21, 2018, 07:03:15 PM »
looks like some sort of datum shift...

verify the CS  and units


I would be interesting to see what contours came out of QGIS from the geotiff to compare as well
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MSTG007

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Re: Civil3D Surface Contours not matching MAP Contours from GeoTiff
« Reply #4 on: September 21, 2018, 09:26:35 PM »
I will try that on Monday with the contours. I hope itís something simple. Thank you Michael!
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huiz

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Re: Civil3D Surface Contours not matching MAP Contours from GeoTiff
« Reply #5 on: September 24, 2018, 03:18:46 AM »
If I remember well it might happen because Civil 3D does not position the Tiff file in the correct way. Tiff files (as also World files) should be placed so that the center of the left upper grid pixel is at the desired location. But Civil 3D places the Tiff so that the top left of the pixel is at the given location.


Since Tiff files are a representation of mean elevations of each square, it is not a huge problem. The smaller the grid, the smaller the problem.
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