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After re-projection output is shifted

  • April 15, 2020
  • 2 replies
  • 102 views
jugoslaviaa
Enthusiast
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Hi all,

In my workbench, I read a polygon dataset (SDE) in the local coordinate system (EPSG:31256) and then I reproject it to EPSG:3857 with help of Reprojector. When I reproject the polygon back to EPSG:31256, I see that my output shifted so it is not as same as when I read the first.

I have tried both CsmapReprojector and Reprojector. I also have tried entering the Source Coordinate System and leaving with <Read from Feature>.

So the polygons looking like this. I would expect them to be identical. Pretty confused. Any idea what I am doing wrong?

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2 replies

david_r
Celebrity
  • david_rCelebrity
  • April 15, 2020

It's not uncommon seeing geometries "drift" when doing repeated reprojections back and forth, it depends a lot on the type of algorithm used for that particular reprojection. Sometimes the amount of shift/inaccuracy is also a function of the placement of the geometry within each coordinate system, this is typically the case for zoned systems like UTM.

How big is the shift in this case, in e.g. meters?

jugoslaviaa
Enthusiast
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  • jugoslaviaaEnthusiast
  • Author
  • Enthusiast
  • April 15, 2020

It's not uncommon seeing geometries "drift" when doing repeated reprojections back and forth, it depends a lot on the type of algorithm used for that particular reprojection. Sometimes the amount of shift/inaccuracy is also a function of the placement of the geometry within each coordinate system, this is typically the case for zoned systems like UTM.

How big is the shift in this case, in e.g. meters?

Actually, I solved the problem after I restart my workbench and used CsmapReprojector and entered the source coordinate system both for projecting and reprojecting back.

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