[Geotiff] User defined datum: Transformation parameters

[Christian Zietz]

Frank Warmerdam schrieb:

> On the pixel-is-point issue, we seem to lack a mechanism to resolve the
> issue, and I find I'm still not keen on the proposed interpretation.

I'm not aware of what the proposed interpretation is nor do I know your
interpretation but the way I understand the GeoTIFF spec it should be as
follows:

Let's assume we've got a 3x3 pixel file. In the case of pixel-is-area
every pixel (n,m) with 0<n<3 and 0<m<3 represents the area with the
bounding box (n,m ; n+1,m+1), so the file fits into the raster
coordinate system like this:

  0   1   2   3
0 +---+---+---+
  |   |   |   |
1 +---+---+---+
  |   |   |   |
2 +---+---+---+
  |   |   |   |
3 +---+---+---+

The center of this image obviously is (1.5,1.5). The total bounding box
is (0,0 ; 3,3).

In the case of pixel-is-point however, each pixel (n,m) represents the
point (*) at (n,m), so the raster coordinate system should look like this:

  0   1   2
0 *   *   *

1 *   *   *

2 *   *   *

The center of the image now is (1,1) and the total bounding box is
(0,0 ; 2,2).

Now listgeo doesn't differentiate between these cases so in my opinion
it gets the second case wrong. Correct me if I'm mistaken.

Christian
-- 
Christian Zietz  -  CHZ-Soft  -  czietz at gmx.net
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