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[McIDAS #KFB-284893]: Converting units in satellite data



Hi Carol,

re:
> Thanks for your patience here. 

No worries.  Stretches are a bit difficult to get one's head around.

re:
> I was under the impression that the stretch
> table was mostly necessary for selecting the proper units outside of
> brightness. 

This and the mapping of unit to brightness.

re:
> The values in SU would ultimately define the BAR as well. 

Yes, and the purpose of the example I sent was to show how to get
the BAR labels to read in FT when the unit of the calibrated
value is M.

re:
> I
> thought the enhancement table (EU) is the only command that would actually
> change the display (color of the pixels). 

Yes, sort of.  An enhancement maps display brightness to colors.  If
you change the mapping of calibrated unit to brightness with a stretch,
you are changing the brightness, and the visual result will be a change
in color.

re
> For instance, here is another
> example with two different SU but the same EU.
> 
> address@hidden ~]$ su.k TABLE L2-CTH
> BREAKPOINTS STORED IN TABLE : L2-CTH.ST
> INPUT       OUTPUT
> -----       ------
> 0             0
> 20000         255
> CALIBRATION TYPE  : ABIN
> CALIBRATION UNITS : M
> BAND NUMBER       : -1
> INTERPOLATION TYPE: LIN
> su.k: DONE
> address@hidden ~]$ su.k TABLE L2-CTH-TEST
> BREAKPOINTS STORED IN TABLE : L2-CTH-TEST.
> INPUT       OUTPUT
> -----       ------
> 10000         0
> 20000         255
> CALIBRATION TYPE  : ABIN
> CALIBRATION UNITS : M
> BAND NUMBER       : -1
> INTERPOLATION TYPE: LIN
> su.k: DONE
> 
> Then I have attached two images. These two images have the exact same
> pixels/colors, but the BARs are different. Light blue maps to 16,000 meters
> in one image versus 12,000 meters in the other image.

The range you specified in the first stretch is not much different from
the mapping of calibrated value (cloud top height) to brightness that
is defined in the 'abincalb.inc' file, so there should not be much in
the way of difference in brightness (brightness -> color via an enhancement)
when using it or not.

The second stretch, on the other hand should have a noticeable effect
since it should be making all pixels for which calibrated values are
less than 10000 black and then ranging the brightnesses (again, colors
via the enhancement) over a subset of the possible calibrated values.

Hmm... I think I now understand the source of the confusion.  The changing
of mapping of calibrated unit to brightness in the stretch will only take
effect when the stretch is specified on the IMGDISP command line via
the SU=<stretch> keyword.  Simply specifying a stretch in the BAR
command without doing so in the IMGDISP command will have no effect on
the mapping of calibrated value to brightness because that has to be
done on image load.

I just tried creating a stretch like your second one, using it in
an IMGDISP load, and my display is black.  I have to think that
this is a telling me that there is something wrong either with
the stretch, or with the code that is doing the conversion during
the IMGDISP.  

re:
> In any case, it's probably just best to stretch over all values for this
> example, so the 0 to 20000 range BAR is the correct one (0 to 65000 for
> feet). I suppose if I did SU MAKE TEST 10000 20000 127 255, that would work
> as well?

I'll need to look into the stretch use with Level 2 products more before I can
comment further.  This will likely be later today as I have some other things
going on this morning, sorry.

Cheers,

Tom
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Ticket Details
===================
Ticket ID: KFB-284893
Department: Support McIDAS
Priority: Normal
Status: Open
===================
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