Bug report #12371

projection problems

Added by Kun Zhang almost 5 years ago. Updated about 4 years ago.

Status:Closed
Priority:Normal
Assignee:-
Category:Projection Support
Affected QGIS version:2.8.1 Regression?:No
Operating System: Easy fix?:No
Pull Request or Patch supplied:No Resolution:invalid
Crashes QGIS or corrupts data:No Copied to github as #:20546

Description

hello, I have used QGIS for several years. The software is great.
But I am not very satisfied with map projection, especially for some classical projection.
When I downloaded for example 'Admin 0 – Countries' data from Natural Earth webpage and do some projection, some issues arouse.
Mercator projection for example, in QGIS 1.8.0, Antarctica disappeared;in QGIS 2.2.0 and QGIS 2.6.1, the bottom of Antarctica converge to a point located on the top-left of the screen.
For azimuthal equidistant projection, the pole projection is OK in QGIS 2.6.1, but when I changed the origin to 'lat_0=31, lon_0=35' for example, many polygons overlap.
Hope the projection functionality would be robust in new versions.

Mercator_EPSG_3857.jpg - Mercator projection (86.8 KB) Kun Zhang, 2015-03-17 12:31 AM

aedq.jpg - aeqd (141 KB) Kun Zhang, 2015-03-17 12:36 AM

aedq.png (116 KB) Raymond Nijssen, 2015-11-05 06:06 AM

History

#1 Updated by Giovanni Manghi almost 5 years ago

  • Category set to Projection Support
  • Status changed from Open to Feedback

Hi,

could you provide a few practical examples attaching sample projects (with sample data) or screenshots/screecasts?

thanks.

#3 Updated by Kun Zhang almost 5 years ago

Hi, please look at the picture attached.One is in Mercator projection (EPSG:3857).
Another is in azimuthal equidiatant projection, the proj4 string is :
+proj=aeqd +lat_0=31 +lon_0=35 +x_0=0 +y_0=0 +datum=WGS84 +units=m +no_defs

the world file is 'Admin 0 – Countries' from Natural Earth. Both projection are done in QGIS 2.6.1

thanks for attention.

#4 Updated by Raymond Nijssen about 4 years ago

You might be using the wrong projection parameters. When I try this one it looks as I expected:

+proj=aeqd +lat_0=31 +lon_0=35 +x_0=0 +y_0=0 +a=6371000 +b=6371000 +units=m +no_defs

Please try again and let us know if it works. Thanks!

According to epsg 3857, this projection only covers latitudes up to about 85 degrees north and south. I guess your data is out of these bounds and not truncated the proper way. I'm using an other world data set and it looks quite ok on my screen.

#5 Updated by Giovanni Manghi about 4 years ago

  • Resolution set to invalid
  • Status changed from Feedback to Closed

closing for lack of feedback.

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