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

[Maciej Sieczka]

Glynn Clements napisa?(a):

> Maciej Sieczka wrote:

> For IEEE single precision, FLT_EPSILON is ~1.2e-7, so a value of
> around 16-17 would have an absolute error of ~2e-6 just due to
> rounding error. "r.info slope" indicates that the range of the data is
> between zero and 52.5, so that error seems reasonable.

>> (A bit OT: what are the Grass equivalents for Gdal's
>> Int16,UInt16,UInt32,Int32,Float32,Float64,CInt16,CInt32,CFloat32,CFloat64?
>>  I'd like to put such note into r.out.gdal manual, it always puzzles me).

> I'm not sure there are equivalents.
>
> Internally, GRASS has three types: CELL (C "int", typically 32-bit
> signed integer), FCELL (C "float", typically 32-bit IEEE
> single-precision floating-point) and DCELL (C "double", typically
> 64-bit IEEE double-precision floating-point).

OK, thanks for clarification. In that case, what are the *most*
appropriate GDAL datatype equivalents for Grass's CELL, FCELL and DCELL?
By "most appropriate" I mean such that gurantee the original data will
be exactly preserved in r.out.gdal output, but as low superfluous
decimal points and bits are required as possible? So that the file is as
small as possible, and that after it is imported back with r.in.gdal, it
is an identical copy of the original one.

>> I was wondering what name should be given to the module. IMO it should
>> replace r.resample and r.bilinear should be removed. Is it acceptable
>> for Grass 6.3?

> I would suggest keeping r.resample. Its output is the result of GRASS'
> built-in resampling, and is exactly what any raster module would
> obtain from reading the map with the current region settings. The
> output from method=nearest in the module which I sent may differ due
> to rounding error.

If I do some checking and it shows it doesn't differ, would that change
your attitude (even the backwards-compatibility could be assured by
setting the default resample method to nearest neighbor (if that's not
the case yet))?

Maciek