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
> > > > >
> > > > >
> > > > >
> > > > >          
>
>