[GRASS-dev] Re: [GRASS-user] r.what and d.what.rast

[Hamish]

Trevor Wiens wrote:
> Javier Álvarez Rodríguez wrote:
> 
> > Hi all,
> > My problem is about I'm obtaining different results when using d.what.rast
> > and r.what. 
> > Using interactively d.what.rast on a map named bas, I obtain these
> > results:
> > 
> > 361421.875(E) 4540953.125(N)
> > bas in DATOS, quant   (854)
> > bas in DATOS, actual  (854.000000)
> > 
> > Then I write x and y coordinates in a file named pp3.txt 
> > 
> > 361421 4540953 (no matter real or integer coordinates)
> > 
> > and when using r.what
> > r.what bas at DATOS < pp3.txt
> > result is 860
> 
> I'm not sure of the cause, but in doing some tests of the same data
> set, it would appear that r.what is probably reporting incorrectly.
> 
> I looked at the code briefly and can't see any obvious errors, but I'm
> ccing the developers list to see if anyone has seen this bug before.


The problem is with d.what.rast when zoomed out:

# spearfish dataset
G63> g.region elevation.10m
G63> d.rast elvation.10m

G63> d.what.rast 

Buttons
 Left:  what's here
 Right: quit

595509.1750503(E) 4920363.03822938(N)
elevation.10m in PERMANENT, quant   (1432)
elevation.10m in PERMANENT, actual  (1432.339600)


G63> r.what in=elevation.10m east_north=595509.1750503,4920363.03822938
595509.1750503|4920363.03822938||1432.65918


1432.339600  !=  1432.65918


G63> r.stats -1gn elevation.10m | grep 1432.3396            
595515 4920365 1432.3396

G63> r.stats -1gn elevation.10m | grep 1432.65918
595505 4920365 1432.65918


Indeed, reported x coordinate is off by one column.


G63> g.region n=4920450 s=n-100  e=595550 w=e-80
G63> d.redraw

G63> d.rast.num elevation.10m

G63> echo -e "width 2\nsymbol basic/circle 30 595509.1 4920363.0 yellow none" \
  | d.graph -m


G63> d.what.rast -c
595509.81707317(E) 4920363.23170732(N), 549(col) 763(row)
elevation.10m in PERMANENT, quant   (1433)
elevation.10m in PERMANENT, actual  (1432.659180)

595510.30487805(E) 4920363.23170732(N), 550(col) 763(row)
elevation.10m in PERMANENT, quant   (1432)
elevation.10m in PERMANENT, actual  (1432.339600)


So it works ok once zoomed in.

G63> r.what in=elevation.10m east_north=595509.81707317,4920364.20731707
595509.81707317|4920364.20731707||1432.65918

G63> r.what in=elevation.10m east_north=595510.06097561,4920364.08536585
595510.06097561|4920364.08536585||1432.3396



#zooming back out:
g.region rast=elevation.10m
d.redraw
echo -e "width 2\nsymbol basic/circle 5 595509.1 4920363.0 yellow none" \
  | d.graph -m
d.what.rast -c

595518.63321799(E) 4920366.76470588(N), 550(col) 763(row)
elevation.10m in PERMANENT, quant   (1432)
elevation.10m in PERMANENT, actual  (1432.462769)

G63> r.stats -1gn elevation.10m | grep 1432.462769   
595515 4920375 1432.462769

now d.what.rast's y is off by one row ...



Hamish


ps - display/d.what.rast/what.c
  if (G_get_c_raster_row (fd[i], buf, row) < 0)

should that be G_get_raster_row(,, type) ??