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Re: 20050802:GeoTIFF max/min values

Unidata Support wrote:


------- Forwarded Message


To: Yuan Ho <address@hidden>
cc: John Caron <address@hidden>,
cc: address@hidden
From: "Steve Ansari" <address@hidden>
Subject: Re: GeoTIFF max/min values
Organization: UCAR/Unidata
Keywords: 200508021512.j72FCJjo008373


Yuan,
Wouldn't that mean that the default range values would be -999.0 to 3.0 (in our case)? ArcMap defaults to: 
High : 3.40282e+038
Low : 1.17549e-038

Steve

Steve,
I mean yes. If you didn't see these values, you could go to Layers Properties, then Symbology to make the changes. After reading John's reply, I think there is one solution that is using greyscale option, and then multiply the scale to the output data. In the greyscale option we replace the missing value with min value. Not a perfect solution, but better then what you see now since no TIFF client can recognize the missing value at this time. This would require to have an API to retrieve the scale too. 

Yuan





Yuan Ho wrote:


Steve Ansari wrote:


Yuan,
I'm not using greyscale. I've printed out the max and min values from the section of GeotiffWriter.java that sets the tag values to verify that the correct max/min values are calculated. It appears that they are. 

    MAMath.MinMax dataMinMax = grid.getMinMaxSkipMissingData( data);
    float min = (float) (dataMinMax.min);
    float max = (float) (dataMinMax.max);
System.out.println(min+","+max); geotiff.addTag( new IFDEntry(Tag.SMinSampleValue, FieldType.FLOAT).setValue( min)); geotiff.addTag( new IFDEntry(Tag.SMaxSampleValue, FieldType.FLOAT).setValue( max)); 

Thanks,
Steve

Steve,
I know why now. It is because of the missing value -999.0. When we calculated the min and max, we skipped the missing value, and Arcmap does not look at the min/max tags, or finds the confliction of tags and data value and takes actual data value -999.0. 

Yuan








Yuan Ho wrote:


Steve Ansari wrote:


Hi John,
I did have one other question...
I've been exporting GeoTIFFs from NetCDF files using the ucar.nc2.geotiff.GeotiffWriter class. When I load the images in ESRI ArcMap the default max and min values are incorrect. Ex) 
High : 3.40282e+038
Low : 1.17549e-038



Steve,
Is the output file greyscale? Otherwise the min and max value should be stored in these two tags: Tag.SMinSampleValue and Tag.SMaxSampleValue. Let me know how do you get these High and Low values, and what are the values of above two tags. 

Yuan
The actual data values are ok and the image is correctly geolocated. It seems that there may be max/min header or tag information that may be missing. 

Thanks,
Steve