[Qgis-developer] Georeferencer produces wrong (shifted) result

[Agustin Lobo]

Manuel,

No, the correct one is the one on the left, which is the one made with
arcgis. I've made an screenshot
with transparency:
https://sites.google.com/site/openfiles2/home/errorgeorefARCG_QGIStransp.jpeg?attredirects=0&d=1
https://sites.google.com/site/openfiles2/home/errorgeorefARCG_QGIStransp.jpegw?attredirects=0&d=1

You can also note it in the first screenshot:
https://sites.google.com/site/filestemp2/home/error_georef.jpg

The points are correct (therefore the errors etc), but the
georeferenced image is shifted. May be the datum is not taken into
account
when the georeferenced image is created.

Agus




2011/12/13 Manuel Massing <m.massing at warped-space.de>:
> Hi Agustin,
>
>
>> Please see the screenshot here:
>
>>
>> https://sites.google.com/site/filestemp2/home/error_georef.jpg?attredirects
>
>> =0
>
>>
>
>> We've tried polynomia of order 1 and 2 and Helmert, with very similar
>
>> results. CRS is ED50 UTM31N
>
>>
>
>> I've uploaded the input layer and points file to:
>
>>
>> https://sites.google.com/site/filestemp2/home/Ilerfly125v2.tif?attredirects
>
>> =0&d=1
>
>> https://sites.google.com/site/filestemp2/home/Ilerfly125v2.tif.points?attr
>
>> edirects=0&d=1
>
>>
>
>
> thanks for your test case.
>
> I did a quick test reprojection, but couldn't see a problem with the
>
> georeferencer output, i.e. the coordinates generated by the transform fit
> the destintaion coordinates within a few pixels, putting the max. error
> somewhere in the ballpark of 1.5m. This relies on the destination
> coordinates being in
>
> ED50 UTM31N. The georeferencer has no support for transforming the
>
> destination coordinates, so they need to be specified in the destination
> CRS.
>
>
> I suspect the discrepancy you are seeing might be a problem with the
>
> WGS84<->ED50 datum transformation, so it would be helpful if you could
> provide
>
> the ArcGIS output as well.
>
>
>> Here you have an screenshot of the comparison to the same image
>
>> georeferenced with ARCGIS (left)
>
>>
>> https://sites.google.com/site/filestemp2/home/errorgeorefARCG_QGIS.jpeg?att
>
>> redirects=0&d=1
>
>> https://sites.google.com/site/filestemp2/home/errorgeorefARCG_QGIS.jpegw?a
>
>> ttredirects=0&d=1
>
>
> I guess you meant to say that the right one is from ARCGIS?
>
>
> cheers,
>
>
> Manuel
>
>
>
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