Yeah and a little more investigation on my part showed me that Arc/Info
ASCII Grid files have their origin in the upper left anyway, even though
they have their lat/long coords in the lower left. This is from
gCore\rasterio.cpp (line 243in 1.6.2). In my RGB reads, with a nPixelSpace
of 3 and a nBufDataSize of 1, I could get away get away with having GDAL
"flip" my file data for me by using a negative value for nLineSpace because
GDALCopyWords handled that. Memcpy doesn't do well with a negative value
for nLineSpace :). It looks like I'll have to have another function flip my
buffer from top to bottom after my RasterIO call.
for(int k=0; k<kmax;k++)
{
if( eDataType == eBufType
&& nPixelSpace == nBufDataSize )
{
if( eRWFlag == GF_Read )
memcpy( ((GByte *) pData) + iBufOffset + k * nLineSpace,
pabySrcBlock + iSrcOffset, nXSpanSize );
else
memcpy( pabySrcBlock + iSrcOffset,
((GByte *) pData) + iBufOffset + k * nLineSpace,
nXSpanSize );
}
else
{
/* type to type conversion */
if( eRWFlag == GF_Read )
GDALCopyWords( pabySrcBlock + iSrcOffset,
eDataType, nBandDataSize,
((GByte *) pData) + iBufOffset + k * nLineSpace,
eBufType, nPixelSpace, nXSpan );
else
GDALCopyWords( ((GByte *) pData) + iBufOffset + k * nLineSpace,
eBufType, nPixelSpace,
pabySrcBlock + iSrcOffset,
eDataType, nBandDataSize, nXSpan );
}
iSrcOffset += nBlockXSize * nBandDataSize;
}
Thanks,
Todd
On Tue, Nov 16, 2010 at 6:22 PM, Kyle Shannon <ksshan...@gmail.com> wrote:
> I am not totally sure, but I believe that the gdal data model always uses
> the upper left corner for the origin, even on files that reference the lower
> left in space. I think this is also the way rasterio handles it. See
> RasterIO docs:
>
> http://gdal.org/classGDALDataset.html#e077c53268d2272eebed10b891a05743
>
> Specifically the nXOff and nYOff parameters.
>
> kss
> # ============================
> Kyle Shannon
> Physical Science Technician
> RMRS Fire Sciences Lab
> Fire, Fuels & Smoke - RWU 4405
> 5775 Highway 10 W.
> Missoula, MT 59808
> (406)829-6954
> kshan...@fs.fed.us
> # ============================
>
>
> On Tue, Nov 16, 2010 at 5:28 PM, Todd Smith <smith.t...@gmail.com>wrote:
>
>> The default way of doing things at my company is to treat the lower
>> left corner of a file as the origin. Thus when I call RasterIO on a
>> GeoTIFF, I make the buffer I pass as pData address to the last row of the
>> buffer I've allocated, and I make nLineSpace negative. This has the effect
>> of reading the file from the beginning, but placing each line into my buffer
>> starting at the last and finishing at the first line. This was working
>> great until I started reading ArcInfo/Ascii files with origins in the
>> lower-left. In this case, I wouldn't want to address to the last row of my
>> buffer, I'd want to address to the beginning of my buffer, and use a
>> positive value for my line space.
>>
>> Is there metadata that will tell me where the file's origin is? If not,
>> any suggestions as to how to deal with this problem?
>>
>> Thanks!
>>
>> Todd
>>
>> _______________________________________________
>> gdal-dev mailing list
>> gdal-dev@lists.osgeo.org
>> http://lists.osgeo.org/mailman/listinfo/gdal-dev
>>
>
>
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