GRASS 7: d.vect grid drawing problem

[neteler]

When importing attached SHAPE file of a 10 degree lines grid, the horizontal lines are not draw. See attachments.

v.in.ogr worldgrid_10deg.shp out=worldgrid_10deg
g.region n=90 s=-90 w=-180 e=180
d.mon wx0
d.vect myworld_political type=area
d.vect worldgrid_10deg

[neteler]

horizontal lines omitted in grid

[neteler]

World grid 10 degrees SHAPE file

[mmetz]

Replying to neteler:

When importing attached SHAPE file of a 10 degree lines grid, the horizontal lines are not draw.

This is because for Lat/Lon, the display drivers draw the shortest line between two vertices (longitude wrapping). A line with two vertices -180,0 and 180,0 has length zero because start and end coordinates are identical, the line is not displayed. Another line with two vertices -10,0 and 10,0 is drawn from -10,0 going east to 10,0 (the shortest line) and not from -10,0 going west over -180, then to 10,0. Special treatment for zero-length lines is not an option because they can appear after vector cleaning.

For the attached shapefile, the horizontal lines need to be broken at their intersections with vertical lines (v.clean tool=break), then the horizontal lines become visible in the display.

[neteler]

Thanks for the explanations, I added a note to the v.in.ogr manual page. Closing.