Helena wrote:
I believe that the error was only in the untis that it has written
out - so everything should have stayed the same except it should
have written ft insted of m. So I had a barscale showing 5000m but
its length was in fact 5000ft. So looking into PROJ_UNITS and
choosing whether to write ft or m should be the fix.
So, if the "meters" setting in PROJ_UNITS is approximately equal to
0.3048, d.barscale should use multiples of feet, otherwise use metres?
I think that it would probably be better to add an explicit option to
d.barscale to select non-metric units.
Also, what to do about large scale factors? d.barscale chooses among a
list of bar size according to the size of the window. Currently, the
available sizes are:
{"10 meters" , 10. , 70., 10},
{"50 meters" , 50. , 200., 5},
{"100 meters", 100. , 700., 10},
{"500 meters", 500. , 2000., 5},
{"1 km" , 1000. , 7000., 10},
{"5 km" , 5000. , 20000., 5},
{"10 km" , 10000. , 70000., 10},
{"50 km" , 50000. , 200000., 5},
{"100 km" , 100000. , 700000., 10},
{"1000 km" ,1000000. ,7000000., 10},
{"10000 km" ,10000000.,70000000., 10}
Presumably the larger scales would use (statute) miles rather than
"kilofeet"? What should the changeover point be? 1 mile (= 5280 feet)?
Anyway, I'll leave it alone for now; at least the length should
actually be as indicated, even if it doesn't use the preferred units.
The length of the bar should be OK, drawing a longer bar may
make it difficult
to place it (it is already pretty long)..
Well, the bar is sized automatically; the change shouldn't cause it to
occupy a larger region of the window than it otherwise would have.
Also some other modules need to be checked for units (e.g. r.profile
and area measurements). The numbers would be probably correct, it is
just the unit written on the screen which is wrong and assumes that
everything is meter. I will check some of the modules and report
what I find.
Again, this is arguably better dealt with via command-line options.
The user doesn't necessarily want to use the same units as the map's
coordinate system.
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.
--
Glynn Clements <glynn.clements@virgin.net>
