topic Re: Reprojection from geographic to EckertIV does not work correctly in Coordinate Reference Systems Questions

Reprojection from geographic to EckertIV does not work correctly

ClintonJenkins — Mon, 24 Nov 2014 11:47:23 GMT

I don't know if this is a bug or a fundamental problem with the conversion from geographic (lat/lon) to an EckertIV projection, but for some polygons it does not work correctly. I have a layer with some polygons that cover a nearly global extent. When they are reprojected to Eckert IV, pieces get cut off, particularly around New Zealand. This also happens if one simply loads the geographic layer into a data frame that is set to EckertIV, and so the projection is done on the fly.

Re: Reprojection from geographic to EckertIV does not work correctly

ClintonJenkins — Mon, 24 Nov 2014 11:51:58 GMT

The same problem seems to occur when reprojecting to Mollweide.

Re: Reprojection from geographic to EckertIV does not work correctly

ClintonJenkins — Mon, 24 Nov 2014 19:41:30 GMT

Below are examples. The original purple layer is geographic, the other two are EckertIV and Mollweide. Notice the area around New Zealand.

Re: Reprojection from geographic to EckertIV does not work correctly

MelitaKennedy — Tue, 25 Nov 2014 20:33:04 GMT

Try densifying the polygons before projecting them. Because it's happening on edges that are curved in the target CRS, I think you have "two-point lines" in the problem areas. ArcGIS doesn't automatically densify when reprojecting data.

You might also run the check geometry tool to see if it finds anything.

Melita

Re: Reprojection from geographic to EckertIV does not work correctly

ClintonJenkins — Wed, 26 Nov 2014 10:18:18 GMT

Aha! Check geometry didn't find anything, but densify seems to work. I'm not sure how practical it will be if it means I have to add lots of extra vertices, since that would make the file bigger, but this does look to be the fundamental problem. Thanks!