Frank,<br><br>Thanks so mush for the quick response.<br><br>One more quick question. I am grabbing the metadata from my image files to store in the database as an index of where my imagery lives. I server out my images in EPSG:4326 so that is how I would like to store the metadata (bounding box) of the images. However I am not really sure how to calculate the metadata for EPSG:4326 in a timely manner.<br>
<br>I.E. if I just pull the metadata from the image file (without reading the image itself) and convert the corner point to EPSG:4236 with CoordinateTransformation I will save some time by not reading the file. However when I serve out the image I need to use gdalwarp to warp the image to EPSG:4326. So the metadata I store in the db does not match the 'real' warped image's metadata.<br>
<br>I can use gdalwarp on each image then pull the metadata but I assume that amount of processing on each image just to get the metadata is going to be a lot slower than just using CoordinateTransformation.<br><br>I index millions of images so the index (pulling the metadata) needs to be somewhat fast.<br>
<br>Can you think of a way that I can get the same metadata as gdalwarp would give for a warped image without actually warping the image?<br><br>Thanks<br><br><div class="gmail_quote">On Fri, May 4, 2012 at 11:23 PM, Frank Warmerdam <span dir="ltr"><<a href="mailto:warmerdam@pobox.com" target="_blank">warmerdam@pobox.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="HOEnZb"><div class="h5">On 12-05-04 03:39 PM, Billy Newman wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
I ran a quick test and confirmed that gdal.AutoCreateWarpedVRT is returning<br>
different results than osr.CoordinateTransformation.<br>
<br>
I.E. I opened a file using:<br>
Dataset dataset = gdal.Open("/images/image.tif")<u></u>;<br>
<br>
I grabbed the corner point and used<br>
osr.CoordinateTransformation.<u></u>TransformPoint(), to transform the point into<br>
EPSG:4326.<br>
<br>
I warped the dataset using gdal.AutoCreateWarpedVRT, grabbed the corner point<br>
and the corner point was a little different.<br>
<br>
I am not sure if that is expected behavior or not. Hopefully I am just missing<br>
some static files and one of the transformations was not quite right. I tried<br>
all the different sampling algos available for the AutoCreateWarpedVRT and that<br>
did not make a huge difference.<br>
<br>
Is warp using a different method to transform the points? If so is that<br>
transformation available via the API?<br>
<br>
I understand that not all calcs may be exact between these two but I would<br>
expect the corner point to be almost exact.<br>
</blockquote>
<br></div></div>
Billy,<br>
<br>
Generally speaking the extents of the warped VRT will be somewhat larger<br>
than the original to capture the irregular shape of the source image after<br>
warping into the target coordinate system.<br>
<br>
Best regards,<span class="HOEnZb"><font color="#888888"><br>
-- <br>
------------------------------<u></u>---------+--------------------<u></u>------------------<br>
I set the clouds in motion - turn up | Frank Warmerdam, <a href="mailto:warmerdam@pobox.com" target="_blank">warmerdam@pobox.com</a><br>
light and sound - activate the windows | <a href="http://home.gdal.org/warmerda" target="_blank">http://home.gdal.org/warmerda</a><br>
and watch the world go round - Rush | Geospatial Software Developer<br>
<br>
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