[GRASS5] LatLong E/W problem in southern hemisphere

[Markus Neteler]

On Fri, Oct 15, 2004 at 06:30:40PM +0200, Roger Bivand wrote:
> On Fri, 15 Oct 2004, Markus Neteler wrote:
> 
> > Hi,
> > 
> > we have a map in LatLong, located somewhere in Argentina:
> > 
> > g.region rast=noaa -p
> > projection: 3 (Latitude-Longitude)
> > zone:       0
> > datum:      wgs84
> > ellipsoid:  a=6378137 es=0.00669438
> > north:      30:24S
> > south:      35:42:00.0036S
> > west:       58:17:59.9964W
> > east:       65:11:59.9892W        <- note this correct value
> 
> Just asking: does Southern hemisphere mean we look at things upside down? 
> Shouldn't east be (yes) east of west, this east is almost 7 degrees west 
> of west, and I think the algorithm is (logically) assuming that you want 
> what is asked for, 353 degrees? Or am I missing something (I wouldn't be 
> surprised!)? Maybe a warning could be useful when the nsres/ewres ratio is 
> so extreme?

Roger, the problem (to me) is that above we have the expected value
65:11:59.9892W, which becomes later 294.800003 
(360 - 294.800003 = 65.2 !). So the wrap around doesn't work (or whatever).

 
GRASS 5.7.cvs > g.region -g
> > n=-30.4
> > s=-35.700001
> > w=-58.299999
> > e=294.800003          <- note the wrong value
> > nsres=0.06309525
> > ewres=4.70800003
> > 
> > The bug seems to be somewhere in libgis, because:
> > 
> > r.in.bin ~/pub/avhrrpf.ndvi.1ntfsa.840101.11705583 output=noaa bytes=1 north=-30.400000  south=-35.700001  east=-65.199997 west=-58.299999 rows=84 cols=75
> > D0/0: E: 294.800003  N:-58.299999
> > D0/0: E: 294.800003  N:-58.299999
> > D0/0: E: 294.800003  N:-58.299999
> > Percent Complete:  100%
> > CREATING SUPPORT FILES FOR noaa
> > 
> > I have added the debug output to
> > lib/gis/adj_cellhd.c
> > (line 103)
> >    G_debug(0,"E: %f  N:%F",cellhd->east,cellhd->west);
> > 
> > Anyone working in the southern hemisphere and observing similar
> > problems?

If east remained -65.199997 instead of becoming 294.800003, everything would
be ok and the test for East > West would work as well.

Markus