[GRASS5] resampling method

GRASS GRASS developer
1

Hi,

can someone (quickly) explain how raster resampling is done when the
region's resolution changes?

cheers,
Hamish

2

Hamish wrote:

Hi,

can someone (quickly) explain how raster resampling is done when the
region's resolution changes?

This is from the GRASSbook p. 98

When resampling from lower to
higher resolution, the high resolution cells are assigned the same
values as the cell within which they are located. When
resampling from higher to lower resolution, the low resolution cell is
assigned the value of the high resolution cell which is located the
closest to its center (nearest neighbor). Resampling is designed for
raster data which represent geometrical features, such as lines and
areas (raster maps with categories). If applied to
raster maps representing continuous fields, the resulting surface may
have a checkerboard pattern.

So for elevation and other continuous surfaces you usually
need to reinterpolate.

Helena

cheers,
Hamish

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3

Helena wrote:

> can someone (quickly) explain how raster resampling is done when the
> region's resolution changes?

This is from the GRASSbook p. 98

When resampling from lower to
higher resolution, the high resolution cells are assigned the same
values as the cell within which they are located. When
resampling from higher to lower resolution, the low resolution cell is
assigned the value of the high resolution cell which is located the
closest to its center (nearest neighbor).

The first part of the above could be omitted. Resampling works the
same way regardless of whether the destination resolution is higher or
lower than the original resolution. I.e. the source cell which is
chosen is that which contains the centre of the destination cell.

Note that, when resampling from lower to higher resolution, a
destination cell isn't guaranteed to be entirely contained by a single
source cell unless the scale factor is an integer.

--
Glynn Clements <glynn.clements@virgin.net>