----- Original Message -----
From: "Jorge Arévalo" <jorge.arev...@gmail.com>
To: "Tamas Szekeres" <szeker...@gmail.com>
Cc: "gdal-dev" <gdal-dev@lists.osgeo.org>
Sent: Friday, August 07, 2009 7:43 PM
Subject: Re: [gdal-dev] Overriding IRasterIO in class derived from
GDALRasterBand
OK, I commented this part during tests, -1 for me. The assertion
disappeared. Many thanks.
And about the time, it's only when executing gdalinfo with options
"-mm -stats -checksum". Takes about 35 seconds, with this image
http://download.osgeo.org/gdal/data/gtiff/utm.tif and one overview of
factor 2 (50% of size in both dimensions). I suppose is normal...
This looks quite slow to me for a modest 512x512 raster.
"gdalinfo -mm -stats -checksum utm.tif" takes less than one second.
You should try to profile what is slow exactly : the DB request (server-side
performance issue ?), the decoding of the result, ...
So, you suggest to copy the block data into the buffer without calling
base implementation of IRasterIO, do you? This implies take care of
the endianess and pixel size "by hand".
Implementing yourself all the cases of IRasterIO will be complicated. Just
look at GDALRasterBand::IRasterIO in rasterio.cpp. If you really want to
implement it, I'd advise you to only concentrate first on a few common
cases, like when the output buffer size is equal to the source buffer size
(nXSize == nBufXSize && nYSize == nBufYSize). For other cases, default to
the base implementation.
Best regards,
Jorge
Best regards,
Tamas
2009/8/7 Jorge Arévalo <jorge.arev...@gmail.com>
Hello,
Context: GDAL WKT Raster driver
In my class derived from GDALRasterBand, I've overrided the methods:
- IReadBlock: Fetch a block from database
- IRasterIO: Should fetch several blocks, that cover an area, and add
them to papoBlocks (cache). The idea is to avoid rounds in the server
AFAIK, the base IRasterIO implementation (in GDALRasterBand), tries to
fetch the block from the cache. If the block isn't in the cache, then
call to IReadBlock. So, the normal way to read blocks in any GDAL
driver should be IRasterIO --> IReadBlock
Then, If I override IRasterIO in my driver RasterBand's class, I
should fetch several blocks in one round and call GetLockedBlockRef to
add these blocks to the cache. After this, call the base
implementation of IRasterIO (in GDALRasterBand) to do its work (see
previous point).
Is it correct? I have problems with my IRasterIO implementation,
because it takes a long time executing until this fail:
ERROR 7: Assertion `nLockCount == 0' failed
in file `gdalrasterblock.cpp', line 228
Is there any mistake in this approach? If not, I suppose I had to
debug my queries, but I'd like to rule our wrong concepts first.
Many thanks in advance.
Best regards,
Jorge
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