[gdal-dev] Problem with gdal1.8 Java bindings gdal.ReprojectImage, produces no data

[William Kang]

Hi Evan,
Thank you for the clearance. I appreciate your helps.


William

On Mon, May 9, 2011 at 3:42 PM, Even Rouault
<even.rouault at mines-paris.org> wrote:
> Le lundi 09 mai 2011 21:32:39, William Kang a écrit :
>> Hi Even,
>> After I set it to 0.125, the speed is comparable to the gdalwarp.exe.
>> Thanks a lot for your suggestions.
>>
>> Aside from this topic, I have some questions about the reprojection
>> process in gdal. My understanding is that the getGeoTransform returns
>> the affine coefficients needed to perform the projection change. If we
>> can calculate the four corner points by using the geoTransformer and
>> get their coordinates in the new projection coordinate system, we can
>> calculate the corresponding bounding box and affine transformation
>> coefficients.
>>
>> But I have read documents and your first reply email suggested that
>> some sampling processes along the image edge are necessary to
>> calculate the proper bounding box. Why is that? Isn't the four corner
>> points enough to determine the new bounding box? Thanks a lot for your
>> help.
>>
>
> The 4 corners are not generally sufficient. It is only a rough approximation if
> you don't want to spend more than 20 lines of coding... Sampling along the
> image edges is required for accuracy, especially in case of important warping
> (for example if you reproject between geographic coordinates <--> polar
> projections)
>
>