[gdal-dev] GDAL ReadRaster thread-safe?

[Tamas Szekeres]

Eric,

You could refer to the RasterIO documentation regarding to these parameters:
http://www.gdal.org/classGDALDataset.html#e077c53268d2272eebed10b891a05743

If you provide your source data then I could try reading it into a GDI+
bitmap object.

Best regards,

Tamas



2009/1/8 Eric Domazlicky <edomazlicky at gmail.com>

> This looks like a great way to go but can anyone explain exactly what the
> bandmap and bandspace parameters are? I know BandMap is an array but what is
> it supposed to represent? I want the image data to be read and put into my
> destination buffer in ARGB format, the source data is in RGBA format. I
> tried making an array with elements in order: 4,1,2,3 but the destination
> data is transparent so I'm thinking the alpha value isn't getting read
> right.
>
> On Wed, Jan 7, 2009 at 4:12 PM, Tamas Szekeres <szekerest at gmail.com>wrote:
>
>> Eric,
>>
>> The most performant option I'm aware of is reading the dataset directly
>> into a bitmap buffer something like:
>>
>> try
>> {
>>         int stride = bitmapData.Stride;
>>         IntPtr buf = bitmapData.Scan0;
>>
>>         ds.ReadRaster(xOff, yOff, width, height, buf, imageWidth,
>> imageHeight, dataType,
>>         channelCount, bandMap, pixelSpace, stride, 1);
>> }
>> finally
>> {
>>         bitmap.UnlockBits(bitmapData);
>> }
>>
>> In this case there's no internal buffers in the marshalling code used by
>> the C# wrappers. The only challenge here is to ensure that the bitmap buffer
>> should have the same structure as the gdal dataset represents. You could
>> refer to the complete example in the C# wrapper for the details:
>>
>> http://trac.osgeo.org/gdal/browser/trunk/gdal/swig/csharp/apps/GDALDatasetRasterIO.cs
>>
>> http://trac.osgeo.org/gdal/browser/trunk/gdal/swig/csharp/apps/GDALReadDirect.cs
>>
>> I don't think if triggering multiple reads for different sections in
>> multiple threads is currently supported by gdal, it might also be driver
>> dependent how the reads are actually implemented by the drivers, however you
>> might anyway try defining separate Dataset objects for the different when
>> performing the read operations, but there might be locks in different places
>> causing the operations to be serialized in effect.
>>
>> Best regards,
>>
>> Tamas
>>
>>
>>
>> 2009/1/8 Eric Domazlicky <edomazlicky at gmail.com>
>>
>>>  I am developing a tiling application and I was hoping to up the speed a
>>> bit by doing some multithreading. What I want to do is start each of 3
>>> ReadRaster calls in seperate threads (using BeginInvoke delegates), then
>>> wait for them to complete and build my RGB image (using EndInvoke). I am
>>> using the C# wrapper to the GDAL library. This multithreaded approach is
>>> showing clear signs of race conditions, with some of the channels not
>>> appearing, random crashes etc. If I ensure each thread completes before I go
>>> on to read the next Raster Band it works fine.
>>>
>>> Is there anyway to make ReadRaster thread-safe? Maybe by disabling
>>> caching which I suspect is the problem.
>>>
>>>
>>>
>>>
>>> _______________________________________________
>>> gdal-dev mailing list
>>> gdal-dev at lists.osgeo.org
>>> http://lists.osgeo.org/mailman/listinfo/gdal-dev
>>>
>>
>>
>
>
> _______________________________________________
> gdal-dev mailing list
> gdal-dev at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/gdal-dev
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.osgeo.org/pipermail/gdal-dev/attachments/20090108/4303b4ed/attachment-0001.html