[gdal-dev] C# bindings for (fast) reproject, resample, and send to DB

[Geospatial Information Technology Solutions]

Why not build an OGC gpkg GEOPACKAGE it supports 4326 tiles
you can extract the tile_data blob if you need to


On Thu, Oct 10, 2019, 5:51 PM <mladen-g at distributel.net> wrote:

>
> Hello,
>
> I've been using GDAL for a while, but I am still a newbie to the API.
> I see there are some experts on this group, so apologies if I'm asking
> something simple (my searches did not reveal the answers I was looking
> for).
>
> Here is my problem:
>
> I need to take an input raster, split into areas of various sizes,
> resample each area into a 256x256 tile, reproject to EPSG:4326 and
> send the resulting pixels to a DB.
>
> GDAL is perfect for this, but I am using the C# bindings and I'm not
> sure what is the most performant way to do it.
>
> I used the following two references to create something that works,
> but I am wondering if it can be improved:
>
> https://gis.stackexchange.com/questions/297831/using-gdalwarp-with-c-bindings
> https://lists.osgeo.org/pipermail/gdal-dev/2017-February/046046.html
>
> How I do it right now:
>
> 1)  Copy the input grid to RAM disk for fast access
> 2)  Invoke Gdal.wrapper_GDALWarpDestName() for reprojection,
> resampling, and output to a /vsimem/ memory-mapped file
> 3)  Read the memory-mapped file into a Dataset (returned by
> wrapper_GDALWarpDestName())
> 4)  Write the Dataset values to DB
>
> What I would like to know:
>
> 1)  To skip the /vsimem file creation, how can I use
> Gdal.wrapper_GDALWarpDestDs() instead of -DestName?  It requires a
> dataset as a parameter, but I am not sure how to initialize it
> correctly.  I've tried Gdal.GetDriverByName("VRT").Create(...) and
> .GetDriverByName("MEM").Create(...), but all the values end up being 0
> when I pass the dataset to wrapper_GDALWarpDestDs()?
>
> 2)  Is there a more direct, efficient way to do what I'm doing?  Here
> is the relevant code
>
> <snip>
> using (Dataset rasterInput = Gdal.Open(inputRasterPath,
> Access.GA_ReadOnly))
> {
>    IntPtr[] ptr = {Dataset.getCPtr(inputRasterPath).Handle};
>    GCHandle gcHandle = GCHandle.Alloc(ptr, GCHandleType.Pinned);
> ...
>     var dss = new
> SWIGTYPE_p_p_GDALDatasetShadow(gcHandle.AddrOfPinnedObject(), false,
> null);
> ..
>     foreach (var tileExtent in overlappingTileExtents) // tileExtent
> just contains minX/minY/maxX/maxY
>     {
>     ...
>
>        string vsiMemFilePath =
> $"/vsimem/{destinationTableName}#{extentName}#tile{indexNumber}.vrt";
>        string[] options = {
>                                  "-of", "VRT",
>                                  "-srcnodata", "99999.9",
>                                  "-dstnodata", "99999.9",
>                                  "-ot", "Float32",
>                                  "-t_srs", "EPSG:4326",
>                                  "-r", "average"),
>                                  "-te", tileExtent.xmin.ToString(),
> tileExtent.ymin.ToString(), tileExtent.xmax.ToString(),
> tileExtent.ymax.ToString(),
>                                  "-ts", "256", "256"
>                              };
>
>         using (Dataset ds =
> Gdal.wrapper_GDALWarpDestName(vsiMemFilePath, 1, dss, new
> GDALWarpAppOptions(options), null, null))
>         {
> ...
>           //read the geotransform + first band and write each pixel
> lat/long + value to the DB
> ...
>         }
>
>      Gdal.Unlink(vsiMemFilePath)
>
> ....
>
> Regards,
> Mladen
>
> _______________________________________________
> gdal-dev mailing list
> gdal-dev at lists.osgeo.org
> https://lists.osgeo.org/mailman/listinfo/gdal-dev
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