Thank you all ! 2012/3/23 Frank Warmerdam <warmer...@pobox.com>
> On Fri, Mar 23, 2012 at 10:29 AM, Chaitanya kumar CH > <chaitanya...@gmail.com> wrote: > > Output pixel value = (raw pixel value * scale) + offset > > Exactly. > > The reason for scale and offset to exist is that "real world" measures > like elevation, temperature, pressure are often represented in raster > datasets as integer values rescaled from some original floating > point values. This is done for compactness in raster format and > because many raster formats don't support floating point pixels at > all. > > So for instance, if you have a dataset with temperatures between > -20 and 100 you might record them in byte values such with an > offset -20 and scale 2.0 which would provide for half degree > precision over the range in byte values. > > So a temperature of 80 would be represented as byte value > of "50". The real temperature would be: > > 50 * 2 - 20 = 80 > > Best regards, > -- > > ---------------------------------------+-------------------------------------- > I set the clouds in motion - turn up | Frank Warmerdam, > warmer...@pobox.com > light and sound - activate the windows | http://pobox.com/~warmerdam > and watch the world go round - Rush | Geospatial Software Developer >
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