Hi David,
Thanks for the report, and a great example showing the problem.
Ferret is seeing the Z axis of the two datasets as being different.
Obviously this should not be the case, as you're opening up the same
file. When opening datasets, Ferret looks to see if an axis is already
stored in memory and reuses ones that are identical. The x and y axes
are matched correctly, but we can see that the Z axis from the second
dataset is renamed to ZAXLEVITR1, so it was detected as different. It
looks like a machine-precision issue, where the coordinate values are
being compared and marked as being different when they are not.
We'll look into why this is happening.
Ansley
David Wang wrote:
Hi Ferreters,
It seems to me that if I load two netcdf files whose variables have the
identical vertical axis, Ferret will still render them as different
ones, and issue a warning message ("*** NOTE: Ambiguous coordinates on
Z axis") when calculations are done among variables. I guess
calculations are correctly done, but the message is somewhat
misleading. Here is an illustrative example:
$ ln -s
$FER_DSETS/data/levitus_climatology.cdf .
$ ferret
NOAA/PMEL
TMAP
FERRET v6.1
Linux(g77)
2.4.21-32 - 03/25/08
2-Oct-08
11:10
yes? use
"$FER_DSETS/data/levitus_climatology.cdf"
yes? use
"./levitus_climatology.cdf"
yes? say
`temp[d=1],return=zaxis`
!->
MESSAGE/CONTINUE ZAXLEVITR
ZAXLEVITR
yes? say
`temp[d=2],return=zaxis`
!->
MESSAGE/CONTINUE ZAXLEVITR1
ZAXLEVITR1
yes? shade/y=0
temp[d=2]-temp[d=1]
*** NOTE:
Ambiguous coordinates on Z axis: TEMP[D=2]-TEMP[D=1]
Thanks,
David
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