用GDAL对影像重采样的一些要点
2007-04-27 15:27 flyingfish 阅读(4335) 评论(0) 编辑 收藏 举报1、RasterIO只能使用最临近插值法
做影像金字塔时，开始用的GDALDataSet的RasterIO通过控制行列宽度来抽层，代码写起来很简洁，奇怪一直没见设置重采样参数的地方，急于实现功能，没有怎么深究，基本功能全都做好后发现分层质量很差。文档里边没找到资料介绍这些，查了很久在Maillist上发现RasterIO() level resampling should all be "nearest neighbour", and so
not introduce any new values.看来不换方法是不行了。
参考资源：http://lists.maptools.org/pipermail/gdal-dev/2005-May/005646.html
On 5/4/05, Sheykhet, Rostic <rsheykhet at sanz.com> wrote:
> Hello,
>
> I am trying to perform RasterIO on a band that references a color
table.
> When the source and destination image dimensions are different, I get
> back a band that has indexes into blank/invalid color table entries.
> I assume this is because of the decimation procedure. Is there a way
> to modify this behavior?
Rostic,
RasterIO() level resampling should all be "nearest neighbour", and so
not introduce any new values. Is it possible you have built overviews
on the file in question with averaging? Perhaps the format is a lossy
compression format?
Best regards,
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2、 GDALWarp的四种采样方式
|
enum GDALResampleAlg |
Warp Resampling Algorithm
Enumerator:
|
GRA_NearestNeighbour |
Nearest neighbour (select on one input pixel) |
|
|
GRA_Bilinear |
Bilinear (2x2 kernel) |
|
|
GRA_Cubic |
Cubic Convolution Approximation (4x4 kernel) |
|
|
GRA_CubicSpline |
Cubic B-Spline Approximation (4x4 kernel) |
|
GDALWarpOpations::eResampleAlg
One of GRA_NearestNeighbour (the default, and fastest), GRA_Bilinear (2x2 bilinear resampling) or GRA_Cubic. The GRA_NearestNeighbour type should generally be used for thematic or colormapped images. The other resampling types may give better results for thematic images, especially when substantially changing resolution.
3、用GDAL Utility实现高质量重采样
===============================================================
NiceResample.cmd
===============================================================
@echo off
echo.
echo. %~n0: resample an image nicely, slow but with good results
echo.
if [%2]==[] goto :Usage
if not exist "%1" goto :NoFile
rem if exist "%2" goto :OutExists
set inFile=%1
set outFile=%2
:: enables variable expansion inside FOR loop (!x! syntax)
:: requires Windows 2000 or newer
setlocal enabledelayedexpansion
:Main
set tmpFile=%infile%
:: resample from 900x900 pixels down to 128x128
:: in 100px stages.
for %%a in (900 800 700 600 500 400 300 200 128) do (
gdalwarp -q -ts %%a %%a !tmpFile! xx_%%a_%inFile%
set tmpFile=xx_%%a_%inFile%
)
:: "&& del" only deletes if previous command successful
gdal_translate !tmpFile! %outFile% && del xx_*_%inFile%
echo.
echo Finished writing 128x128px %outFile%
goto :EOF
:NoFile
echo *** Error: input %1 not found
goto :EOF
:Usage
echo. Usage: %~n0 [input image] [output image]
echo.
echo output overwritten if it exists
goto :EOF
===============================================================
参考：Resampling With GDAL库
http://www.nabble.com/Resampling-With-GDAL-t3611789.html
4、使用调色板的影像只能使用nearest neighbour采样方式。
For indexed images change the resampling to nearest neighbour (-rn)
rather than bilinear, cubic or cubic spline (-rb, -rc, -rcs):
