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January 2007
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2007.01.17 21:51 "Re: Elevation Data", by Frank Warmerdam
Joris wrote: > I'm starting to see where you guys are coming from... > > But still, ZeroIsBlack and MinIsBlack are different names for the same > grayscale we *all know* encodes black as zero. It is unsigned. I don't > care if Craig feels it's elevation data. He's writing grayscale. Joris, I believe Craig talked about using a signed, not unsigned type. In that context MinIsBlack and ZeroIsBlack are different things. > I keep repeating myself. Though there may be no need to do so. I came up > with a recommendation that I think agrees with the spec, agrees with > imaging needs, and allows Craig to redefine ranges to match his view of > metres metric and sea level = 0 elevation data. Is there anything in > that recomendation (http://www.asmail.be/msg0055261416.html) that you > see conflicts with any needs or with de facto usage (as far as the > latters is consistent)? My concern is with this statement: """ It is also valid, and recommended as a second best choice, to use any other range. In this case, writing out the SMin/SMax tag is obligatory. """ My concern is that it conflicts with widespread existing usage which is to write out data such as elevation with a photometric interpretation of MINISBLACK and no SMin/SMax values. I would prefer the statement to read as: """ It is also valid, and recommended as a second best choice, to use any other range. In this case, writing out the SMin/SMax tag is encouraged. """ I also have no intention of following the following reader advice: """ If the SMin/SMax tags aren't present, readers are recommended to take that as a firm indication the standard 'intrinsic' range is use. """ So, all things considered I'm inclined to leave things in the current ill defined state which is working fine for me rather than commit to your language. That said, I'd like to write SMin/SMax, but due to the progressive streaming nature of my writers it isn't especially easy for me to include them. Best regards, -- ---------------------------------------+-------------------------------------- I set the clouds in motion - turn up | Frank Warmerdam, warmerdam@pobox.com light and sound - activate the windows | http://pobox.com/~warmerdam and watch the world go round - Rush | President OSGeo, http://osgeo.org