[GRASS5] probs with i.points

Markus Neteler neteler at itc.it
Tue Oct 2 16:20:35 EDT 2001

Hi Heiko,

On Mon, Oct 01, 2001 at 02:54:04PM +0200, Heiko Kehlenbrink wrote:
> Hi again!
> I'm currently working with a series of big (my opinion) aerial photos,
> each a .tiff about 380 mb (11200*11200 pixel).
> Importing and viewing is working fine , with a little patience of
> course.
> I have 10 shoots in 2 rows , so i begun with the third in the upper row
> (#3) as the origin in a x-y location.
> I identified identic points in the overlap area with i.point (i.point3
> won't work, it seems it forgot the identified points every time i wanted
> to use the analyse-funktion, displaying something like "not enough
> points marked out" although i did, anyway).

[yes, unfortunately there are some bugs in i.point3, however, this
module is much more convenient than i.point]

> With i.rectify (using 1 degree transformation) i got nice results using
> air shoot number #3 (middelst in 1st row) as reference for the direct
> neighbours (#2 and #4).
> Trying to use the newly georeferenced photo #2 to identify points in
> number 1 i.points crushed with  a message:
> +------------------------------------------+------------------------------------------+
> |                                          |
> |                                          |
> +-------------------------------------------------------------------------------------+
> |Use mouse now
> ...Speicherzugriffsfehler                                              |
> GRASS:/spare/gisdata/grass/bin

segmentation fault - mhhh. Could you run this again using "strace i.points"?
Perhaps this hels a bit to find the problem. Of course a debugger would
be much better, see
in the source code for how to debug.

I am also using i.points regularly without problems.

> I tried with  downskaled tif of 90 mb - same effect.
> If i used the very small overlapping strip between photo #1 and #3  to
> identify points - i.rectify worked (poor results of course).
> The same in the second row...

Well, since you are working in an xy-location, how can your images

Generally: It is much more recommended to use i.ortho.photo to
rectify aerial images. Only then the results will be really accurate.

Kind regards

 Markus Neteler

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