On 18.11.2015 11:59, Bar Ori wrote:
Thanks Ari for your reply.
In my situation, sometimes I am working with rectangles and sometimes
not. Depends the source of information.
I thought to always use the GCPs as follows:
In case my shape has rectangular form, so the dataSet.GetGCPCount()
will return me “0” and I will use the dataSet.GetGeoTransform(),
otherwise, will use the dataSet.GetGCPs().
The issue is that for setting the GCPs, I must put the coordinate in
the middle of pixel (that is why I subtract “0.5”). If I wouldn’t, so
yes, the geotransform values would be correct.
Is it a bad practice? Should I figure out the shape from start and to
take two different steps?
I don't know the best answer to that. I'm just assuming if you do it
with some GUI tool for example it will report you pixel coordinates in
integer values.
Ari
*From:*gdal-dev [mailto:gdal-dev-boun...@lists.osgeo.org] *On Behalf
Of *Ari Jolma
*Sent:* 18 November 2015 11:35
*To:* gdal-dev@lists.osgeo.org
*Subject:* Re: [gdal-dev] GCPsToGeoTransform returns wrong values
Bar,
I think you are setting the GCPs up wrongly if you want them to be at
the corners.
GCP(LeftDown.X, LeftDown.Y, LeftDown.Z, Height - 0.5, null, "4") does
not have 0 before Height-0.5.
GCPsToGeoTransform checks the special case of GCPs in rectangular
shape and in top-left, top-right, bottom-right, bottom-left order and
returns the exact transform the dataset has.
I'm not sure if it makes sense to have real values for the pixel
coordinates although they are real values.
Best,
Ari
On 18.11.2015 09:32, Bar Ori wrote:
Hi,
I noticed something that for me looks weird and I would like to
know maybe I am doing something wrong.
If not, how should I overcome this behavior.
I set 4 GCPs as follows:
vargcps = new[]
{
newGCP(LeftUp.X, LeftUp.Y, LeftUp.Z, 0.5, 0.5, null, "1"),
newGCP(RightUp.X, RightUp.Y, RightUp.Z, Width - 0.5, 0.5, null, "2"),
newGCP(RightDown.X, RightDown.Y, RightDown.Z, Width - 0.5, Height
- 0.5, null, "3"),
newGCP(LeftDown.X, LeftDown.Y, LeftDown.Z, Height - 0.5, null, "4")
};
And when I am doing as follows:
vargeotransform = newdouble[6];
Gdal.GCPsToGeoTransform(gcps, geotransform, 0)
Or (after using dataSet.SetGCPs(gcps, projection) :
vargeotransform = newdouble[6];
dataSet.GetGeoTransform(geotransform);
So the values returned, are wrong.
For example, if the LeftUp.X was 35.01050 so the value of
geotransform[0], which supposed to be the same value, can be 35.0082.
The same with all the geotransform values.
If I am getting from the dataset and setting again, every time it
is changing more and more.
Is there any connection to the use of the “0.5”?
Thanks.
**
**
*Ori Bar |***Software Developer
Applications Development
Elbit Systems Land and C4I
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