ArcGIS Pro - Clip (Modify Features) aggregates nearby geometry

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04-13-2021 08:54 AM
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SvenHemmelder
New Contributor II

I have a large polygon that contains several several other (smaller) polygons. Some of these smaller polygons also intersect with each other but they all at least 'touch' the larger polygon.

Now I wanted to clip this larger polygon with a unionized version of these smaller polygons (i.e. symmetrical difference/erase depending on your GIS of choice). There are several ways you can do this but most of these require several steps and some temporary files. Thankfully, ArcGIS Pro has a Clip editor tool that should allow me to do all necessary steps at once and inplace (i.e. just modifies the existing geometries). It unfortunately does appear to aggregate nearby polygons (not touching) even when the optional buffer is set to 0.

You can test this yourself by opening a new feature class and drawing 2 nearby (again, not touching) rectangles (i.e. the input features) enclosed by a larger square (i.e. the target feature; see screenshot).

screenshot.PNG

Is there some environmental setting that I'm not aware of that causes this behaviour? I'm running ArcGIS Pro 2.5.2

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Scott_Harris
Esri Regular Contributor

My best guess is that the distance is less than the XY tolerance of the data. What are the XY tolerance and resolution on that dataset? This article outlines a way to fix problems caused by non-standard resolution/tolerance values (I can't say this is one of those problems without access to the data): https://www.esri.com/arcgis-blog/products/arcgis-pro/analytics/geoprocessing-resolution-tolerance-an...

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Scott_Harris
Esri Regular Contributor

Hi @SvenHemmelder 

Can you please show us the result?

I think I set my data up like you have, and have Clip using the same method (Discard) and 0 buffer distance,

Before:

Scott_Harris_0-1618330915694.png

 

After (I also moved the input polygons out of the way to show the result):

Scott_Harris_2-1618331050498.png

Is this different than your result?

Thanks,

Scott

 

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SvenHemmelder
New Contributor II

Hi Scott, thanks for your reply!

Yeah, my results are different. Here's another snippet illustrating the aggregation. It's pretty weird, the lines of the new inner ring doesn't even completely follow the vertices of the input features.  

SvenHemmelder_0-1618334690754.png

Might be worth mentioning that we're talking about very small geometries. The exact distance between the input features isn't even displayed with ````Measure distance````:

SvenHemmelder_1-1618335053808.png

 

   

 

Scott_Harris
Esri Regular Contributor

My best guess is that the distance is less than the XY tolerance of the data. What are the XY tolerance and resolution on that dataset? This article outlines a way to fix problems caused by non-standard resolution/tolerance values (I can't say this is one of those problems without access to the data): https://www.esri.com/arcgis-blog/products/arcgis-pro/analytics/geoprocessing-resolution-tolerance-an...

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SvenHemmelder
New Contributor II

I think I've found the problem. In short, it appeared as though the clip tool from Modify features (not from Analysis Tools) somehow aggregates nearby features (see https://imgur.com/NCWBAsF). I have since figured out that this probably has to do with the XY Tolerance. Sadly, this value is only exposed as a parameter for clip from Analysis Tools and only as an environment variable from ArcGIS Pro 2.6 onwards.

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SvenHemmelder
New Contributor II

@Scott_Harris Missed your reply initially but relieved that we both came up with the XY Tolerance part :) I'll check out your link and continue from there, thanks! 

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SvenHemmelder
New Contributor II

It was indeed the XY tolerance. This value dictates the minimum value between coordinates and was unfortunately much larger than the distances between some of my input features. The easiest way to fix it in ArcGIS Pro < 2.6 was to just configure the XY Tolerance in a new geodatabase and to copy the feature class there. Clip from Modify Features now works as expected when given this feature class.

Thanks again @Scott_Harris!  

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Scott_Harris
Esri Regular Contributor

I'm glad you have it resolved :)

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