Martin Wegmann wrote:
I found a weird behaviour in r.resamp.stats which causes a shift of the
resulting image but only on a large scale (subcontinental scale, shift to
south-west).
I tried to reproduce it with the spearfish dataset but failed.
Doing it on Africa srtm DEM (res based on gtopo30 DEM):
g.region -g
...
res=0.00083333
..
g.region res=0.0083333
r.resamp.stats input=dem output=dem_resampstats method=average
produces this output of a small region with islands shown in the jpg (overlay
with original raster)
any idea how to fix this? regards, Martin
--- raster/r.resamp.stats/main.c 15 Nov 2006 03:57:24 -0000 1.8
+++ raster/r.resamp.stats/main.c 7 Dec 2006 05:59:11 -0000
@@ -80,13 +80,13 @@
for (col = 0; col <= dst_w.cols; col++)
{
double x = G_col_to_easting(col, &dst_w);
- col_map[col] = (int) floor(G_easting_to_col(x + 0.5, &src_w));
+ col_map[col] = (int) floor(G_easting_to_col(x, &src_w) + 0.5);
}
for (row = 0; row <= dst_w.rows; row++)
{
double y = G_row_to_northing(row, &dst_w);
- row_map[row] = (int) floor(G_northing_to_row(y + 0.5, &src_w));
+ row_map[row] = (int) floor(G_northing_to_row(y, &src_w) + 0.5);
}
Instead of adding half a cell (to locate the midpoint rather than the
north-west corner), I was adding half a map unit.
For a projected location, the offset was half a metre (or foot), which
is negligible. For a lat-lon location, the offset was half a degree,
which is rather more significant.
Fixed in CVS.
--
Glynn Clements <glynn@gclements.plus.com>
