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Using ChangeDetector to compare GeoJSON and Shapefile versions


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I'm attempting to confirm that a set of GeoJSON area features are geometrically identical to a Shapefile produced from the same source. Of the 19k features, less than 400 come out as Unchanged, with the rest going to Inserted AND Deleted. I've set match Geometry to 2D and turned ON Lenient Geometry Matching.

 

When I write the same GeoJSON out to Shapefile, the resulting Shapefile gets all of its features routed to Unchanged under the same settings.

 

Any ideas as to why I'm seeing this behavior?

Best answer by markatsafe

@ret3​  We recently presented a couple of webinars on Change Detection, Part 1 & Part 2. The first one might give you some ideas on what's going wrong here. Some possible ideas:

  • if you have complex geometry, they might not match the way esri stores geometry. Sometimes you have to round the coordinate (CoordinateRounder) but there might be other changes, like reversing the direction of donut holes.
  • what's in your 'where_clause' attribute? is that join being done correctly?

If these thoughts don't help, it might help if you could post a sample of your data here, otherwise you might need to contact your FME reseller for support so they can look at the problem and your data more closely.

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  • Best Answer
  • January 15, 2021

@ret3​  We recently presented a couple of webinars on Change Detection, Part 1 & Part 2. The first one might give you some ideas on what's going wrong here. Some possible ideas:

  • if you have complex geometry, they might not match the way esri stores geometry. Sometimes you have to round the coordinate (CoordinateRounder) but there might be other changes, like reversing the direction of donut holes.
  • what's in your 'where_clause' attribute? is that join being done correctly?

If these thoughts don't help, it might help if you could post a sample of your data here, otherwise you might need to contact your FME reseller for support so they can look at the problem and your data more closely.


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  • Author
  • January 15, 2021

I didn't find any correlation to complex geometries, but I did find one between failed matches and excess coordinate precision! I'll get a corrected GeoJSON set and try again.

(FYI, I wasn't using a where clause - just feature classes where all the contained features were included)

Thanks!


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