Hamish:
> I'm noticing when using d.zoom in a lat/lon location that the
> resolution is not preserved, and I need to run 'g.region
> res=$ORIG_RES -a' to fix it afterwards.
> Is this a bug or a feature?
Markus:
To me it looks like a bug
...
I briefly looked into this a few weeks ago but didn't it.
Maybe you are able to fix that?
Bug #1:
Right then. Increasing the significant digits on the rounding
calculation in set.c seems to have fixed it for resolutions up to
0:00:00.0001 (3mm)
The "13" below is arbitrarily large, it was just an easy value to
insert in vi. 
Index: src/display/d.zoom/cmd/set.c
RCS file:
/home/grass/grassrepository/grass/src/display/d.zoom/cmd/set.c,v
retrieving revision 1.3
diff -u -r1.3 set.c
--- src/display/d.zoom/cmd/set.c 25 Sep 2002 04:46:44 -0000
1.3
+++ src/display/d.zoom/cmd/set.c 27 Jul 2004 07:59:45 -0000
@@ -50,8 +50,8 @@
resetres = 1;
while ( resetres ) {
- nsr = round_to(window->ns_res, 3);
- ewr = round_to(window->ew_res, 3);
+ nsr = round_to(window->ns_res, 13);
+ ewr = round_to(window->ew_res, 13);
td = ceil (north / nsr);
tnorth = td * nsr;
*Note there are several more calls to round_to() using sd=3 in the
code. It's all a bit too convoluded for me to follow so I've left
them as-is for now.
The change makes the round_to() function in set.c do:
+while( rint(foo) < pow(10,12) )
-while( rint(foo) < pow(10,3) )
Will that break anything on wierd platforms/compilers?
Anyone have ideas why 3 was used aside from it being about right
for res=meters?
But I'm thinking I'm missing the whole point of the "resetres" while-loop
by making the rounding so exact? ie, why not just 'nsr=window->nsres' ...
Markus:
(at least it's annoying because when zooming on continental scale you
often get an error that you left the max latitude etc).
Bug #1.5:
I think this happens regardless, e.g.
G:~> g.region n=90N s=90S e=180E w=180W res=0:05
G:~> d.redraw
G:~> d.zoom
[middle click for unzoom]
360 -> reset
north:90:02:50.28N south:90:02:50.28S east:179:59:19.32W west:179:59:19.32E
North, south, east limit of default region reached.
WARNING: G_set_window(): Illegal latitude for North
ERROR: region for current mapset is invalid
line 3: <north: 90:02:50.28N>
run "g.region"
i.e. 90N + res/2, 90S - res/2
The sig. digits patch attached makes the above error into:
north: 90:05N south: 90:05S east: 180E west: 180W
this is because of the following code on lines 56-63:
td = ceil (north / nsr);
tnorth = td * nsr;
... etc
when north is 90. (nsr is nsres=0:05 here)
cheap fix is on line 64 add something like
if (window->proj == PROJECTION_LL ) {
if(tnorth>90)
north=90;
if(tsouth<-90)
tsouth=-90;
//e,w?
}
but that's not a proper fix, I think a lot of the set.c code assumes
res>1 and might need to be rewritten.
??
So that's the where & how it's screwing up anyway ... hopefully that's
enough for it to be easily fixed by someone more familiar with the code.
Hamish