Hello,
Im working a project using gdal to slice TMS style png tiles. The code
currently works, but I'm running into some trouble optimizing to run fast
enough for use on mobile devices.
My current strategy:
Open the source data(currently testing with BSB):
Get the transform, using GDALGetGeoTransform, and get the inverse transform
get coordinate transformers from dataset coordinates to lat/lon
store all that for when tiles are needed
When a tile is needed:
Determine the pixel coordinates of the source data that is needed, taking into
account a clip line for the data that is not at the edge of the source image.
Create a new VRT using VRTCreate(tileSize, tileSize)
Copy data to the VRT:
VRTAddSimpleSource(destBand, sourceBand,
sourceDataRegion.origin.x, sourceDataRegion.origin.y,
sourceDataRegion.size.width,
sourceDataRegion.size.height,
destDataRegion.origin.x, destDataRegion.origin.y,
destDataRegion.size.width, destDataRegion.size.height,
"NEAREST",
VRT_NODATA_UNSET
);
Create a copy the VRT slice as PNG
GDALDriverH pngDriver = GDALGetDriverByName("PNG");
GDALDatasetH pngCopy = GDALCreateCopy(pngDriver, path.UTF8String,
datasetToWrite, false, NULL, NULL, NULL);
GDALClose(pngCopy);
Currently GDALCreateCopy is using 70% of the total CPU time
I've tried reusing the same VRT, but did not see a significant speed increase
from that.
Is there a more CPU efficient way to do this? Should I be creating a vet of
the whole dataset warped to the target CRS using GDALAutoCreateWarpedVRT then
slicing tiles from that?
Any suggestions for optimizing this would be greatly appreciated.
Also see that attached screenshot at
https://s3.amazonaws.com/com.gaiagps.static/Screenshot_4_9_13_4_58_PM.png for a
breakdown of CPU usage
Thanks,
Jesse Crocker_______________________________________________
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