[Met_help] intersection/union area question
Faye Barthold
Faye.Barthold at noaa.gov
Wed Mar 24 12:24:20 MDT 2010
Hello,
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?
Thanks!
Faye
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