[OSM-talk] People's Map

andrew heggie list at sylva.icuklive.co.uk
Fri Apr 10 22:31:25 BST 2009


On Friday 10 April 2009 22:05:15 Martin Spott wrote:
> D Tucny wrote:
> > How much does a small plane with camera mount cost to hire for a day? :)

I don't know about a day but 17 overlapping images of an approximately 10 by 
10 km area cost me GBP600. Once rectified they were not true "plan" images 
being slightly oblique. I guess the best images would be taken higher ( mine 
were 14000ft IIRC) with a longer lens to reduce parallax errors.
>
> It depends on wether you're going to invite the pilot for a nice
> meal  :-)
> I think the most tricky part of the story is still to rectify and
> adjust the resulting aerial imagery. If you managed to develop a
> procedure for this step, please let me know  ;-)

Jukka Rahkonen showed me how to do it with gdal_translate and gdalwarp. It's a 
lot easier than it looks at first.

Essentially the first bit burns ground control points into the image the 
second then stretches the image and produces a geoTIFF from it. I visited 4 
ground control points with my GPS each about 3km apart and at prominent 
points near the corners of each image. I suggest you need farm ore ground 
control points than this at this scale because my georectified image was up 
to 20 metres adrift in some parts.

This would be easier if there were a way of deriving a LAT/LONG from OSM

AJH




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