[Met_help] intersection/union area question

Faye Barthold Faye.Barthold at noaa.gov
Wed Mar 24 12:24:20 MDT 2010


I am comparing MODE output from MET v1.0 and MET v2.0 (running on two 
separate machines) in preparation to upgrade to MET v2.0.  All of the 
output that I'm interested in is identical between the two versions with 
the exception of the intersection area, union area, and ratio of the 
intersection to union area.  In general, all three variables seem to 
have higher values in the output from version 2.0.  For example:

intersection area from MODE (v1.0) = 83
union area from MODE (v1.0) = 326
ratio from MODE (v1.0) = 0.722

intersection area from MODE (v2.0) = 112
union area from MODE (v2.0) = 387
ratio from MODE (v2.0) = 0.974

I've looked through the user guides and release notes for each version 
and can't find anything that might indicate a change in how these values 
are being calculated.  Is there a reason that these values would be 
different between the two versions?  Since the areas seem to be larger 
overall in v2.0, is that version somehow more sensitive and therefore 
defining larger object areas?  Also, how is the ratio of the 
intersection area to the union area being calculated?  I had assumed 
that it was simply intersection area divided by union area, however the 
values in the MODE output for the ratio don't make sense relative to the 
individual intersection and union area values.  Using the v2.0 example 
above, the ratio given by MODE is 0.974.  Calculating the ratio as 
intersection area (112) divided by union area (387) gives a ratio of 
only 0.289.  Am I missing something with this calculation?


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