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這幾天用GDAL處理DRG數(shù)據(jù)時(shí)發(fā)現(xiàn)，有數(shù)據(jù)被處理成了黑板，什么都沒有，發(fā)現(xiàn)是因?yàn)镈RG圖像顏色比較簡單，使用了調(diào)色板的緣故。 使用SetColorTable將調(diào)色板寫入后，一部分基本正常，但還有些圖像還是有黑板的現(xiàn)象。仔細(xì)察看出錯(cuò)的DRG與正常的DRG的區(qū)別，發(fā)現(xiàn) C:\Program Files\FWTools1.0.5>
C:\Program Files\FWTools1.0.5>gdalinfo D:\RasterTest\DRG\I48E010019DRG.TIF
Driver: GTiff/GeoTIFF
Size is 6946, 5715
Coordinate System is `'
Origin = (636178.308000,3822519.830000)
Pixel Size = (4.00000000,-4.00000000)
Metadata:
TIFFTAG_XRESOLUTION=317.5
TIFFTAG_YRESOLUTION=317.5
TIFFTAG_RESOLUTIONUNIT=2 (pixels/inch)
Corner Coordinates:
Upper Left ( 636178.308, 3822519.830)
Lower Left ( 636178.308, 3799659.830)
Upper Right ( 663962.308, 3822519.830)
Lower Right ( 663962.308, 3799659.830)
Center ( 650070.308, 3811089.830)
Band 1 Block=6946x1 Type=Byte, ColorInterp=Palette
Color Table (RGB with 256 entries)
0: 128,0,128,255
1: 78,125,208,255
2: 194,226,255,255
3: 150,240,100,255
4: 200,240,170,255
5: 150,105,66,255
6: 255,255,255,255
7: 150,150,150,255
8: 0,0,0,255
9: 0,0,0,255 C:\Program Files\FWTools1.0.5>gdalinfo D:\RasterTest\DRG\I49E012003DRG\2.TIF
Driver: GTiff/GeoTIFF
Size is 1705, 1425
Coordinate System is `'
Corner Coordinates:
Upper Left ( 0.0, 0.0)
Lower Left ( 0.0, 1425.0)
Upper Right ( 1705.0, 0.0)
Lower Right ( 1705.0, 1425.0)
Center ( 852.5, 712.5)
Band 1 Block=1705x4 Type=Byte, ColorInterp=Gray 還是調(diào)色板沒處理好，查遍資料發(fā)現(xiàn)沒有什么特別的地方，最后仔細(xì)跟蹤錯(cuò)誤代碼，在GDAL代碼中找到

/* -------------------------------------------------------------------- */

/* Check if this is even a candidate for applying a PCT. */

/* -------------------------------------------------------------------- */

if( poGDS->bCrystalized )

{

CPLError( CE_Failure, CPLE_NotSupported,

"SetColorTable() not supported for existing TIFF files." );

return CE_Failure;

}

百思不得其解，折騰了半天最后在GDAL-DEV看到這段：

I think the key here is that the GeoTIFF driver in GDAL庫 only allows you to assign a pseudocolor table to a file before you start any raster data. 察看代碼，發(fā)現(xiàn)把SetColorTable放在了RasterIO，Write之后了，修改后就好了。

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