[gdal-dev] NODATA value in an array from RasterIO

[Limei Ran]

Hi Frank:

I used:
int pbHaveNoData;
double fNoData = poBand->GetNoDataValue( &pbHaveNoData );

I got:
pbHaveNoData = 0;
fNoData =  -10000000000.000000

The image is GByte image.  Does it mean the image does not have nodata 
value since pbHaveNoData = 0?  I viewed the image in arcGIS, it has a 
lot of nodata value areas.  How can I update the image by assigning some 
pixels to NODATA based on some conditions?

Thank you a lot for your help,

Limei


Frank Warmerdam wrote:

> Limei Ran wrote:
>
>>
>> Hi:
>>
>> I am reading a region out from a band using RaterIO into an array.  
>> What are NODATA cell values in the array?  Are they 0 or something 
>> else?  Can I modify the array and write back to the image.  How do I 
>> keep NODATA values in the array to be on the image after writing?
>
>
> Limei,
>
> Nodata cells will have some particular pixel value.  You can use the
> GetNoDataValue() method on a gdal.Band object to determine what it's
> nodata pixel value is.  It should be None if there is no reserved
> nodata pixel value.
>
> How to preserve nodata pixels depends on the circumstances.  Is your
> concern keeping nodata pixels unchanged through a series of arithmetic
> operations on the image array?  Or setting the "nodata metadata" properly
> on the output dataset?
>
> Best regards,