[OSM-talk] ping OpenAerialMap

[Jukka Rahkonen]

 <list <at> sylva.icuklive.co.uk> writes:

> 
> On Sun, 12 Oct 2008 08:48:36 +0000 (UTC), Jukka Rahkonen wrote:
> 
> >> I've some aerial photos that I need to find how to georeference, 4MB 
> >> jpegs and 17 overlapping tiles, is there a program you can 
> >> recommend?
> >
> >
> >Could you tolerate a non-integrated system and measure pixel coordinates and
> >corresponding true world coordinates with a separate program and feed in these
> >ground control points from command line? 
> 
> If you mean can I attribute a single pixel in the image with a
> coordinate on the ground then yes. I'm not a programmer or a
> cartographer just a pc user but can use the command line.
> 
> >In this case you could use
> >gdal-programs (gdal_translate and gdalwarp) and get a single mosaiced
> >georeferenced image.  Download FWTools package, it includes both gdal
> tools and 
> OpenEV Viewer that can be used for defining ground control points.
> 
> OK I'll have a look, thanks. I've previously used a free windows
> mapping program but it uses a metre grid and even when projected with
> british OS datum and co ordinates its 70m out (even the control points
> get displaced) so I have some sort of problem with the datum and
> projection.

Hi,

First step is to measure ground control points and insert them 
into image file.
 That is done with gdal_translate and -gpc option.  Read:
http://gdal.org/gdal_translate.html

Command line will be something like:
gdal_translate -of GTiff -gcp [...] -gcp [...] -gcp [...] input.jpg  with_gpc.tif

Now you'll have a new image "with_gpc.tif".  Next step is to use 
gdalwarp.  If you have given coordinates as WGS84 lat/lon 
degrees and you'd like to keep the same projection (epsg:4326) 
it should go this way:

gdalwarp -of GTiff -s_srs epsg:4326 -t_srs epsg:4326 with_gpc.tif
final_georeferenced_tif_image.tif

This is right from my head and I cannot guarantee that commands are
totally correct but they should be close to working.  You can 
output into whatever projection you like, output to different 
file format.  You can also mosaic all your images together once 
they have ground control points measured. However, try
to keep things simple in the begining and start playing 
with individual images.