[ferret_users] minor issue: "Ignoring erroneous point

[ferret_users] minor issue: "Ignoring erroneous point_spacing=even attribute."

To: ferret users <ferret_users@xxxxxxxx>

Subject: [ferret_users] minor issue: "Ignoring erroneous point_spacing=even attribute."

From: Ryo Furue <furue@xxxxxxxxxx>

Date: Fri, 3 Jul 2020 22:51:05 +0900

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Ferret Team,

I searched our mailing archive but didn't find it there.

My original netCDF file has an x axis like

float lat = 9.95, 10.05, 10.15, . . .

without the "point_spacing=even" attribute.

I open the file in PyFerret and save just one timestep (L) into a new file:

save/file=tmp.nc/l=10 var

I then open this new file and PyFerret says,

*** NOTE: Axis "LAT" is irregular. Ignoring erroneous point_spacing=even attribute.

Indeed the new file has gotten the "point_spacing=even" attribute.

I come across this problem from time to time. (Today I reproduced this on PyFerret v7.5 on Linux.)

The axis is a single-precision real and the gridpoints may not be precisely represented. So, I'm not surprised that this axis isn't regarded as "even". That is, PyFerret is doing the right thing when it reads the new netCDF file. So, it's probably a mistake that it added the "even" attribute when it saved the data.

Strangely, the longitude axis -0.05, 0.05, 0.15, . . . , which originally didn't have a point_spacing attribute either, got a point_spacing = "uneven" attribute in the new file!

Cheers,

Ryo