[Thread Prev][Thread Next][Index]

Re: [ferret_users] curious Ambiguous coordinates on Z axis



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

[Thread Prev][Thread Next][Index]

Contact Us
Dept of Commerce / NOAA / OAR / PMEL / TMAP

Privacy Policy | Disclaimer | Accessibility Statement