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SubtractFeatures problem

dave hoeffgen

dave hoeffgen

Resource contributor
Messages
1,439
Country
germany
Hi,
for building not to intersect a road I used the "line to poly" function and then the "SubtractFeatures" one.
After hours of processing and a result like there was no subtraction attempt applied I decided to make a test.

So I quickly made this shapefile in QGIS:
shapes.jpg


The yellow poly has the attribute "test=2", the two others have "test=1".
I used the following code:

Code: 
ImportOGR|...\test.shp|*|*|AUTODETECT


SubtractFeatures|test=2|test=1|1.5

ExportOGR|*|ESRI Shapefile|...\test.shp|test

#paths are removed for privacy, they are not identical

The exported shapefile is written OK, but nothing is "subtracted", basically input and output files are identical.

Is this a limit to the feature, is This not how it is meant to be used? Is it limited to polygons which are completely inside each other?

Thanks in advance for any clarification.

Regards,
Dave
 
Hi Dave,

Nope, this should work. Are there any messages in the log from the subtract step? And can you attach the test shapefile so that I can try here?
 
I'll attach them later when i get home. The next step would be subtracting two polygons from each other which have the same attribute values. Should this work too?
 
Thanks, I'll have a look at them.

No, subtracting polygons with the same attributes won't work, since you can't select them in that case.
 
Oops, no, sorry completely forgot to check this issue.
 
Hi,

I found out what the issue was. Your test attribute has the type of string, not integer. So you filter should be like this:

Code: 
SubtractFeatures|test="2"|test="1"|1.5

Then it works. With the new and improved tooltips you can now hover above a variable and see what the type is.
 
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