[gdal-dev] Can GDAL open binary buffer contents as input for MEM format?

[Roger André]

Hi Frank,

Thanks for the example.  How can I specify alpha in that, for one of the
quantized 8-bit PNG's (with alpha) that MapServer produces?

They look like this:

Metadata:
  Software=UMN Mapserver
Corner Coordinates:
Upper Left  (    0.0,    0.0)
Lower Left  (    0.0,  256.0)
Upper Right (  256.0,    0.0)
Lower Right (  256.0,  256.0)
Center      (  128.0,  128.0)
Band 1 Block=256x1 Type=Byte, ColorInterp=Palette
  NoData Value=0
  Color Table (RGB with 85 entries)
    0: 0,0,0,0
    1: 251,0,0,64
    2: 250,0,0,54
    3: 253,0,0,114
    4: 254,0,0,176
    5: 254,0,0,224
    6: 254,0,0,228
    7: 254,0,0,252
    8: 253,0,0,168
    9: 254,0,0,170
   10: 254,0,0,234
   11: 254,0,0,246
   12: 254,0,0,230
   13: 252,0,0,194
   14: 253,0,0,232
   15: 254,0,0,248
   16: 254,0,0,226
   17: 253,0,0,252
   18: 254,0,0,244
   19: 254,0,0,240
   20: 253,0,0,248
   21: 254,0,0,192
   22: 250,0,0,98
   23: 252,0,0,98
   24: 253,0,0,236
   25: 251,0,0,144
   26: 253,0,0,208
   27: 252,0,0,252
   28: 253,0,0,250
   29: 253,0,0,226
   30: 254,0,0,212
   31: 253,0,0,242
   32: 250,0,0,112
   33: 253,0,0,238
   34: 253,0,0,222
   35: 254,0,0,208
   36: 253,0,0,234
   37: 254,0,0,236
   38: 254,0,0,232
   39: 252,0,0,150
   40: 253,0,0,240
   41: 251,0,0,114
   42: 253,0,0,244
   43: 254,0,0,222
   44: 231,0,0,255
   45: 202,0,0,255
   46: 249,0,0,255
   47: 96,0,0,255
   48: 63,0,0,255
   49: 229,0,0,255
   50: 89,0,0,255
   51: 248,0,0,255
   52: 192,0,0,255
   53: 230,0,0,255
   54: 88,0,0,255
   55: 176,0,0,255
   56: 225,0,0,255
   57: 206,0,0,255
   58: 64,0,0,255
   59: 53,0,0,255
   60: 113,0,0,255
   61: 169,0,0,255
   62: 183,0,0,255
   63: 252,0,0,255
   64: 184,0,0,255
   65: 251,0,0,255
   66: 247,0,0,255
   67: 189,0,0,255
   68: 224,0,0,255
   69: 250,0,0,255
   70: 244,0,0,255
   71: 243,0,0,255
   72: 227,0,0,255
   73: 241,0,0,255
   74: 253,0,0,255
   75: 246,0,0,255
   76: 167,0,0,255
   77: 168,0,0,255
   78: 254,0,0,255
   79: 242,0,0,255
   80: 245,0,0,255
   81: 44,0,0,255
   82: 161,0,0,255
   83: 0,0,0,255
   84: 255,0,0,255


Roger
--

On Sat, Jan 16, 2010 at 1:26 PM, Frank Warmerdam <warmerdam at pobox.com>wrote:

> Roger André wrote:
>
>> Hi All,
>>
>> I'd like to know if I can take the results of a MapServer Python mapscript
>> 'mapImage.getBytes()' operation, and feed it into GDAL as a data source for
>> an in-memory raster?  The MapServer docs state that the results of
>> 'getBytes' in Python is a "string of binary data".  I'm not sure if GDAL can
>> open this sort of object though.
>>
>> For background purposes, the reason I would like to do this is so that I
>> can try replacing PIL with GDAL in TileCache for the cutting of metatiles.
>>  PIL isn't properly saving the image formats generated by MapServer, whereas
>> GDAL replicates them perfectly.
>>
>
> Roger,
>
> I am not aware of a way to utilize a raw buffer as a mem dataset from
> Python (though this is doable from C++).  However, you can just write
> the buffer to a mem dataset.  This code snippet from the autotest suite
> shows something like this:
>
>    #######################################################
>    # Setup dataset
>    drv = gdal.GetDriverByName('MEM')
>    gdaltest.mem_ds = drv.Create( 'mem_1.mem', 50, 3, gdal.GDT_Int32, 1 )
>    ds = gdaltest.mem_ds
>
>    raw_data = array.array('f',list(range(150))).tostring()
>    ds.WriteRaster( 0, 0, 50, 3, raw_data,
>                    buf_type = gdal.GDT_Float32,
>                    band_list = [1] )
>
> It is slightly more tricky with what I assume is a pixel interleaved 3
> band image you would have.  Without having tested it, something like this
> might work:
>
>  mem_ds = gdal.GetDriverByName('MEM').Create('x',200,300,gdal.GDT_Byte,3)
>  mem_ds.WriteRaster( 0, 0, 200, 300,
>                      mapImage.getBytes(), 200, 300, gdal.GDT_Byte,
>                      band_list=[1,2,3],
>                      buf_pixel_space=3,
>                      buf_line_space=3*200,
>                      buf_band_space=1)
>
> Good luck,
>
>
> --
>
> ---------------------------------------+--------------------------------------
> I set the clouds in motion - turn up   | Frank Warmerdam,
> warmerdam at pobox.com
> light and sound - activate the windows | http://pobox.com/~warmerdam<http://pobox.com/%7Ewarmerdam>
> and watch the world go round - Rush    | Geospatial Programmer for Rent
>
>
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