[GRASS-user] barscale with lat/long projection

[Hamish]

Brandon M. Gabler wrote:
> I'm using GRASS 6.2, and want to add scale/north arrow to maps. My  
> location is in lat/long projection, and I'd prefer to leave the  
> location that way - is there a way to do this? Or will I need to  
> start a new location with a different projection, and import my files 
> to that?


As scale is different in lat/lon NS and EW directions (Plate Carrée
projection) drawing a distance scale is not allowed. As you move north
or south, the horizontal scale changes as cos(lat). (other popular GIS
software may let you draw one, probably due to high customer demand, but
it is still very misleading to do so)

Use d.grid instead. Or d.graph with a compass symbol if you like:
G63> echo "symbol extra/fancy_compass 75 5 90 black red" | d.graph
maybe with a "N" above that (d.text).

I have just made a change in 6.3-cvs so you can do "d.barscale -n" from
a lat/lon location without error. [devs: I think it would be better to
rewrite the -n flag to use a symbol and then display that with
D_symbol() vs. current way using direct screen drawing commands.]

Another code change might be to modify d.barscale to report distance
units in degrees for lat/lon, not meters/feet.



Hamish