[Qgis-user] Mosaicking aerial images

[Andreas Neumann]

Thank you Morgan. This sounds promising. I will definitely try gdalwarp 
and the cblend switch! I will report back about the result.

Thanks a lot for the hint!

Andreas


On 11.12.2014 19:08, morgan-hesperus wrote:
> When I need a blended mosaic of overlapping images, I've had good results
> using gdalwarp's -cblend switch, as follows.
>
> 1. Open the overlapping images in QGIS.
> 2. Create a new polygon layer. This is so you can create a masking polygon
> for one of the images.
> 3. Draw a masking polygon whose edge cuts through the overlap area where
> you want blending. (The rest of the polygon can be outside the image.)
> Save.
> 4. Go Raster>Extraction>Clipper.
> 5. Choose Mask layer and select your polygon.
> 6. If your image has only three bands, check Create alpha band. Don't
> check this if your image already has 4 bands.
> 7. Specify an output file. This cannot already exist.
> 8. Edit the command line at the bottom to replace the "-clip-to-cutline"
> switch with "-cblend 40". The 40 is just a suggestion. It means the new
> image will fade to completely transparent across the 40 pixels around the
> polygon edge.
> 9. Hit OK. The image produced will have an alpha channel and fade from
> fully opaque to fully transparent along the clipping polygon edge.
>
> - Morgan
>
>
>> Message: 3
>> Date: Wed, 10 Dec 2014 12:21:14 -0600
>> From: Michael Treglia <mtreglia at gmail.com>
>> To: Andreas Neumann <a.neumann at carto.net>,
>> 	"qgis-user at lists.osgeo.org" <qgis-user at lists.osgeo.org>
>> Subject: Re: [Qgis-user] Mosaicking aerial images
>> Message-ID:
>> 	<CAPKp32vuf8OmVenc=fh54xnnQSTnWp0J31=aR0dvBppXBA7TVQ at mail.gmail.com>
>> Content-Type: text/plain; charset="utf-8"
>>
>> Hi Andreas,
>>
>> I'm Bringing this back to the list, as others here probably have some
>> better thoughts than I do.  Googling around, I found this tool which
> might
>> be useful (?), though I can't tell how it handles overlaps [haven't even
>> downloaded it...]: https://trac.osgeo.org/gdal/wiki/Correlator
>>
>> Not sure about enblend (can't access the site right now)
>>
>> Depending on how different the images are, you could just try mosaicing
> and
>> see what it looks like (gdal_merge takes the values of last image added
> for
>> overlaps).  If there's a way to standardize color values based on
>> brightness, or by RGB bands, that might help, either before or after
>> mosaicing. (might depend on if you're dealing with multi-band image, or
>> single band? - it would be fairly easy on multi-band like Landsat)
>>
>> Hope that helps,
>> mike
>>
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