Sid World file origin

[skorte]

Is the origin of a SDW file the upper left corner or the middle of the pixel?

[rparker]

I believe they describe the middle of the upper-left pixel.

From the docs (see 5. and 6.):
The world file format is six lines, each line containing a double precision value (represented in text). No additional lines may be present. Leading and trailing whitespace are allowed.

The meanings of the six values are:

1. dimension of a pixel in map units in x direction
2. first rotation term
3. second rotation term
4. dimension of a pixel in map units in y direction
5. x-coordinate of the center of the upper-left pixel
6. y-coordinate of the center of the upper-left pixel

The y-dimension is, by convention, a negative value.

GeoExpress ignores the rotation term in most cases.

Example

This is an example of a world file:

0.20000000
0.00000000
0.00000000
-0.20000000
780.10000000
219.90000000


This world file indicates the image resolution is (0.2, -0.2) and the upper-left is at (780.1, 219.9). The rotation terms are zero, meaning no rotation is required.