[GRASS-dev] barscale in latlong region

[Michael Barton]

How about making d.barscale be approximately accurate in latlon near the
bottom of the map and say so in the docs? Not ideal, but useable perhaps.

Michael


On 7/2/07 11:56 PM, "Hamish" <hamish_nospam at yahoo.com> wrote:

> Michael Barton wrote:
>> 
>> I know this has come up before, but I wanted to see if there might be
>> a way to fix this now.
> 
> see  http://thread.gmane.org/gmane.comp.gis.grass.devel/2794/focus=2841
> 
>> I don't work much with latlon locations, but I know that a lot of
>> people do. For large areas especially, it is one of the main ways to
>> manage geospatial data. GRASS has pretty good tools for dealing with
>> latlon and its idiosyncrasies. However, a peculiar gap is that the
>> barscale tool won't work in latlon. Given that I'm told that there are
>> GRASS libraries already in existence to deal with latlon to metric
>> conversions, it seems odd that we can't put a scale on a latlon map.
>> 
>> Is this actually a very difficult problem to solve, or just one that
>> no one has yet gotten around to doing--I know that you all have sooo
>> much free time on your hands ;-)
> 
> 
> It's a problem of correctness, not a technical/time issue.
> A horizontal plate carrée scale is only valid at a single lat, and
> becomes more wrong as you zoom out or look up and down the map. See a
> National Geographic map for a solution which has a series of scales in
> the shape of a horn, where you choose a scale depending on the lat.
> 
> 
> Glynn's suggestion in the above thread of changing the units to degrees
> (or min,sec) could work. But then you could use d.grid for that.
> 
> 
> note "d.barscale -n" will work in lat/lon as that doesn't need scale.
> (north arrow only). Better: replace "d.barscale -n" with a symbol so you
> can optionally draw the compass or fancy_compass under the "N" text
> instead of the arrow-head.
> 
> 
> Hamish

__________________________________________
Michael Barton, Professor of Anthropology
Director of Graduate Studies
School of Human Evolution & Social Change
Center for Social Dynamics & Complexity
Arizona State University

phone: 480-965-6213
fax: 480-965-7671
www: http://www.public.asu.edu/~cmbarton