Contours split into tiny segments

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02-18-2022 11:36 AM
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ArthurKay
New Contributor III

Previously running a contour tool I would get nice continuous polylines output. Now I am getting zillions of line segments with 10-30 vertices each. My work around has been to use unsplit lines to rejoin them into continuous polylines, which works but is a little  annoying extra step.

I thought it had something to do with the size of the raster being too large. Now I've done a contour at a single value (using contour list) on a fairly modest extent (~1x1 mile) and it produced a contour made of 4,000 features. Any ideas why this is happening?

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SteveLynch
Esri Regular Contributor

The contour lines should be a single line per interval unless you've specified a value for "Maximum vertices per feature" but I don't think that is the case because you are having the same problem with ContourList.

What version of ArcGIS are you using, how many columns and rows is the input raster, have you set any environments?

Could you zoom to an area which includes a few of these short segments and take a screen shot of the contours, symbolized on something that'll show them as segments, and the input raster.

Could you post the output from ContourList (i.e. zip and attach to post)?

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ArthurKay
New Contributor III

Hey Steve, thanks for the response. For some additional detail: Initially I was trying to run an arcpy command that generates contours based on map view extent on a mosaic dataset. However sometimes the issue seemed to persist beyond that and occur on standard raster DEMs and using the standard gp tool ui. To play it safe I restarted my computer, and am making a copy of the raster extent from the mosaic dataset before running the contour command. This seems to solve the problem. I think running contours directly on a mosaic dataset can lead to inconsistent results but I could be wrong. 

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SteveLynch
Esri Regular Contributor

Please keep me posted via this thread or via email slynch@esri.com

You could use RasterCopy, with output to .tif for example, when making a copy of the raster extent from the mosaic dataset and remember to, in the tool's environment, set SnapRaster = input Mosaic

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ArthurKay
New Contributor III

Hey SteveLynch, just had a situation where I tried to generate contours with extent env manager on raster mosaic dataset, same problem (lots of little segments). Then I used copy raster with extent env on the mosaic dataset, then just standard contour tool (no extent needed) on the copy raster and contours worked fine.

This is was a simple work around and not a big deal. Previous testing just hadn't been as conclusive. I am now on latest version of ArcGIS now (2.9.2) was either on 2.9.0 or 2.9.1 before. 

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IanDesjarlais
New Contributor

Steve- this is occuring for me in ArcGIS Pro 3.1.0.   I am getting over 4000 segments for what should only be 5 polylines.   Is there a definitive resolution for this?  Ive been having to export everything into QGIS to make contours but that seems weird considering we pay "big bucks" for the 3d/Spatial Analyst Extensions.

Any suggestions would be appreciated!

thanks!

 

ian d

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SteveLynch
Esri Regular Contributor

Ian

Please email (slynch@esri.com) a zipped copy of the raster and a list of the parameters that you are using.

-Steve

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Wayne_Rennick
New Contributor III

Same issue here. 
For me I think the elevation dataset I'm using "somehow" (meaning I did it) was assigned "Double precision" 64 Bit pixel depth which is way more detail than I need for an elevation dataset. Exporting the data to a new Floating point 32-bit raster dataset did the trick. 

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