Dear list,

I use GEOS 3.9.0 via an R library (sf). I have been trying to find the 
intersection between groups of lines and a polygon / multipolygon.

I have realised that updating the packages on my machine has resulted in some 
strange intersection results on Windows machines (and only Windows - works on 
mac and ubuntu). The sf update which introduced the issue was also associated 
with a change in GEOS versions, upgrading from 3.8.0 to 3.9.0 and the suspicion 
is that it is something in GEOS rather than the sf R library.

I have searched the tickets but could not see any issues which seem to match 
what I am seeing.

I attach an image below of the results I am getting with the intersection 
between the lines and the polygon on my Windows machine. Red lines are the 
lines which were not considered part of the intersection and the thicker green 
lines are what was identified as the intersection between the grid of line 
segments and the polygon. It seems all lines that intersect the polygon 
boundary are correctly identified but only some lines that are entirely within 
the polygon boundary are included in the intersection.
[cid:9cf2cef6-266a-43ce-87d5-091c21f4b907]
I had initially reported this as an issue in sf and there are more examples 
there: https://github.com/r-spatial/sf/issues/1781


Question 1: Is this a known issue with 3.9.0?


Question 2: Is there an easy way to directly install 3.9.1 on to a Windows 
machine to test the behaviour with the latest version?


Many thanks for your help,


Laura


Dr. L Marshall

Centre for Research into Ecological & Environmental Modelling

University of St. Andrews


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