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I'm learning how to use Oblique Mercator projection in QGIS 3.4.7. I created a custom projection with "omerc" and passed two points (New York City, USA and Tokyo, Japan) as the parameter.

Extent: Extent not known
Proj4: +proj=omerc +lat_1=35.652832 +lon_1=139.839478 +lat_2=40.728157 +lon_2=-74.077644 +ellps=GRS80

I loaded the country shape file from Natural Earth to layer.

However, when I apply my custom projection, the map has distortion at the edges. The edges of the maps are unexpectedly connected.

screenshot of distorted image

Can somebody share how to solve this problem?


I found that proj4 omerc demo image also has the same problem of zingers.

proj4 omerc page also shows zingers

  • While not antipodes, Tokyo and New York are far, far apart, and the shortest line passes over the International Date Line. You might need to alter the data to range longitudes 0-360, not -180-+180. – Vince May 1 at 15:07
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    You're getting 'zingers'--polygons are split by the edge of the projected CRS but not clipped so the lines are connecting points on opposite sides. One solution is to clip out those polygons before projecting the data. Oblique Mercator can be difficult to determine what needs to be clipped. – mkennedy May 1 at 16:12
  • @mkennedy and Vince Thank you for response! For 'zingers', I initially thought it's a common already-solved problem, but not able to find documents on zingers via Google. It seems a good problem to tackle with. – suztomo May 2 at 13:31
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    Zingers may be an Esri-specific term. We've certainly had similar questions here before. – mkennedy May 2 at 18:15

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