[GRASS-user] integration of sample.c algorithms into r.resample

[Glynn Clements]

Glynn Clements wrote:

> > > 1. the output is not quite correct when the region is not aligned to the input 
> > > raster, including edge effects
> > 
> > Actually r.bilinear is all screwed:
> > http://intevation.de/rt/webrt?serial_num=2790
> > 
> > There are two issues. Please see my most recent posts and Urs Gruber's
> > post dated Tue, Feb 14 2006 17:16:21.
> 
> First, r.bilinear reads the input map as integer CELL values
> (G_get_c_raster_row).
> 
> Second, it adds 0.5 to the interpolated result, then writes the output
> map as FCELL. I would guess that the 0.5 is because it originally
> rounded to the nearest integer.
> 
> If the output mostly or wholly contains values with a fractional part
> of 0.5, that suggests that the sample coordinates are falling exactly
> on the cell centres, so the u and t interpolation fractions are zero,
> resulting in the output value being an integer input value plus 0.5.
> 
> Changing it to read the input as FCELL or DCELL rather than CELL would
> be trivial. I'll commit a patch to do that (read and write DCELL), as
> well as remove the +0.5.

I've done this. A simple test with the output region equal to the
input map's region results in an exact copy (other than the
CELL->DCELL conversion).

-- 
Glynn Clements <glynn at gclements.plus.com>