[GRASS5] [bug #3296] (grass) i.rectify: automatic resolution calculation is wrong

[Request Tracker]

this bug's URL: http://intevation.de/rt/webrt?serial_num=3296
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Subject: i.rectify: automatic resolution calculation is wrong

The automatic target resolution calculation in i.rectify is bad.


imagery/i.rectify/get_wind.c

[w1 is starting window, w2 is target window]

    w2->ns_res = (w2->north - w2->south) / w1->rows;
    w2->ew_res = (w2->east  - w2->west ) / w1->cols;


Say you have a map which is much taller than it is wide and after
rectification it will be rotated 90 degrees to be very wide but not very tall.
The above code will leave the resultant map with many divisions in the
vertical, and few in the horizontal, ruining the data quality. The effect is
less and less obvious as the rotation nears 0 or 180 degrees.

any ideas on how to fix this?

the previous step is calculating the georeferenced versions of the source
map's 4 corners. (which has its own problems...)



Hamish


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