[GRASSLIST:3997] Re: ps.map grid in Lat/Lon

> > i'm want to  overlay a map of a Lat/Lon location with a grid that
> > has less than 1 degree spacing.
> > is that possible? (geogrid is not available for lat/lon and if i use
> > 
> > grid nothing happens when i choose a spacing less than 1)
> >
> I had a similar problem back with GRASS 5.0.0.  I was told at the time
> 
> that ps.map did not support floating point grids, hence the problem 
> with lat-long locations.  I don't know if it has been fixed, but a 
> simple workaround is to make a vector grid with v.mkgrid and just 
> display that along with whatever else you want with ps.map.  Thanks to
> 
> whomever suggested that to me.


The attached patch adds this to ps.map in GRASS 5.7.

Before trying that though you might try the "geogrid" command [5.7
only], which will draw a lat/lon grid over a non-Lat/Lon location map.

I haven't put this in CVS as it needs some checking over to make sure it
doesn't cause other problems (eg it tests grid==0 when 0 is now floating
point). Maybe someone with a keener eye for C than me can comment.
It might be better to just work on getting geogrid to do lat/lon?


Results on the map look great, formats text into deg:minutes, but you
may need to use a lot of precision to get 5-minute ticks to round
correctly. e.g., for 5' use something like "grid 0.08333333333333"

This makes the mapinfo command look pretty wonky for anything smaller
than 0.25 of a degree though. I guess G_format_easting() could fix that?


e.g., for the global lat/lon dataset:  [zoom in]

ps.map out=test.ps << EOF
raster nations
grid 0.25
  numbers 1
  end
mapinfo
  where 0.5 8.5
  end
end
EOF
gv test.ps



Hamish

latlon_grid.diff
Description: Text document