Oblique projection (Ob): Partly wrong annotations

[yvonnefroehlich]

Description of the problem

Related to this forum post https://forum.generic-mapping-tools.org/t/how-to-set-the-annotation-of-x-axis-as-latitude-when-i-use-oblique-projection/4751/13

Here, I try to summarize the main findings so far.:

• Overall there is an issue with the annotations for the Oblique projection Ob. Partly the West-East and South-North directions are mixed up.
• The issue does not occur in GMT 6.1.0 (please see https://forum.generic-mapping-tools.org/t/how-to-set-the-annotation-of-x-axis-as-latitude-when-i-use-oblique-projection/4751/7?u=yvonnefroehlich).
• Explicitly setting --MAP_ANNOT_OBLIQUE=anywhere can help to fix the issue in some cases. However, the documentation states that this is the default (please see https://docs.generic-mapping-tools.org/dev/gmt.conf.html#term-MAP_ANNOT_OBLIQUE).
• Appending / not appending +v to -J has an effect whether the issue occurs.

Full script that generated the error

Case I (GMT forum)
Top Left

gmt grdimage @earth_relief -JOb168/51/172/32.5/6c -R-500/2300/-400/400+uk -Ggray -BeNsW -Bxa5f1 -Bya5f1 -png lon_lat

Top Right

gmt grdimage @earth_relief -JOb168/51/172/32.5/6c+v -R-500/2300/-400/400+uk -Ggray -BeNsW -Bxa5f1 -Bya5f1 -png lon_lat_v

Bottom Left

gmt grdimage @earth_relief -JOb168/51/172/32.5/6c -R-500/2300/-400/400+uk -Ggray -BeNsW -Bxa5f1 -Bya5f1 --MAP_ANNOT_OBLIQUE=anywhere -png lon_lat_anywhere

Bottom Right

gmt grdimage @earth_relief -JOb168/51/172/32.5/6c+v -R-500/2300/-400/400+uk -Ggray -BeNsW -Bxa5f1 -Bya5f1 --MAP_ANNOT_OBLIQUE=anywhere -png lon_lat_anywhere_v

Top Left: Wrong	Top Right: Correct

Bottom Left	Bottom Right

Case II (PyGMT docs)
Top Left

gmt coast -JOb130/35/25/35/6c -R130/35/145/40+r -Ggray -BWSNE -Bxa5f1g5 -Bya2f1g2 -png lon_lat_02

Top Right

gmt coast -JOb130/35/25/35/6c+v -R130/35/145/40+r -Ggray -BWSNE -Bxa5f1g5 -Bya2f1g2 -png lon_lat_v_02

Bottom Left

gmt coast -JOb130/35/25/35/6c -R130/35/145/40+r -Ggray -BWSNE -Bxa5f1g5 -Bya2f1g2 --MAP_ANNOT_OBLIQUE=anywhere -png lon_lat_anywhere_02

Bottom Right

gmt coast -JOb130/35/25/35/6c+v -R130/35/145/40+r -Ggray -BWSNE -Bxa5f1g5 -Bya2f1g2 --MAP_ANNOT_OBLIQUE=anywhere -png lon_lat_v_anywhere_02

Top Left: Correct	Top Right: Wrong

Bottom Left	Bottom Right

Full error message

No error message occurs.

System information

• Operating system: Windows and Linux
• GMT version (gmt --version): GMT 6.5