[GRASS5] Re: [GRASSLIST:4019] d.zoom in lat/lon?

[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 

A few d.zoom bugs really, (mostly) fixed now.


> > Bug #1:
> > 
> > Right then. Increasing the significant digits on the round_to()
> > 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. ;)

[but later tests showed anything less than 13 didn't fix the problem]


I didn't like that approach, so in the end I left that as it was and did
some checking & resetting just before the call to G_adjust_Cell_head()
rather than rewrite the entire program. This fixes zoom+unzoom or -f pan
circumnavigations too.


> > > (at least it's annoying because when zooming on continental scale
> > > you often get an error that you left the max latitude etc).
> >
> > Bug #2:
> > 
> > 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

fixed. (there was a longitude bug as well which would leave you with a 
one column wide region sometimes)



The changing resolution bug wasn't just for lat/lon, it would mess up on
UTM as well if you set res=3.333333333333333333 for example. It was just
pronounced in lat/lon as resolution is usually fractional.
res=0:30 was ok.


So d.zoom should be a lot more robust now, but it is still not 100%;
e.g. if res=0:05 sometimes the north/south bound will stick at 89:55
even if you make the box way off into the NULLs. fix: 'g.region n=90'
Sometimes zooming in on individual cells is a bit trial and error too.


Now that we can zoom properly for lat/lon, there's another bug somewhere
in the display code for non-integer lat/lon maps:


G:~> g.region n=90N s=90S w=150E e=150W
G:~> d.rast etopo2.CELL
[displays ok, centered on 180deg longitude]

G:~> r.mapcalc etopo2.DCELL='double(etopo2.CELL)'
G:~> d.rast etopo2.DCELL
ERROR: cell_values_d: xdr_double failed for index 359.

G:~> g.region n=90N s=90S w=150W e=150E
G:~> d.rast etopo2.DCELL
[displays ok, centered on 0deg longitude]



!, ?,
Hamish