[GRASS5] [bug #939] (grass) d.barscale ignores PROJ_UNITS

[Eric G. Miller]

On Mon, Mar 04, 2002 at 01:59:59AM +0000, Glynn Clements wrote:

> > > While we're on the subject of units, I note that GRASS' "foot"
> > > (according to src/libes/gis/proj3.c) is the international foot
> > > (0.3048m) rather than the US survey foot (0.3048006096m). Is this
> > > correct? It isn't likely to be a problem for measurements (the
> > > difference being 2 ppm), but it could be a significant problem for
> > > coordinates.
> > 
> > Yea, I think that's incorrect.  It should be using the "old" survey
> > foot.
> 
> So, what to do about it?
> 
> Simply changing 0.3048 to 0.3048006096 might mess up users' existing
> data. OTOH, there's possibly a fair number of cases where the data is
> already messed up but the user doesn't realise it.

I don't know how many places that feet/meters conversion is used.  It
might be worthwhile to do a little investigation to see how significant
the effects might be.  Say, if you took a state plane map, and projected
it to UTM, if that conversion was used, then significant error likely was
introduced (provided the state plane was in feet, not meters).  We need
to keep both, but differentiate between the International Foot, and the
U.S. Survey Foot.  I think there may be places that use the
International Foot for mapping ??

Anyway, probably little point in changing it until the whole projection
code gets fixed up.

-- 
Eric G. Miller <egm2 at jps.net>