define axis/x=65.0:65.0/npoints=1/unit=degree lon
define axis/y=8.0:8.0/npoints=1/unit=degree lat
!define axis/z=0:500:5/npoints=100/DEPTH/unit=meter depth
file/var=depth/format=(F700.2) zaxis
define axis/z/depth/npoints=100/unit=meter/name=depth/from_data depth
**ERROR: improper grid or axis definition: data for DEFINE AXIS/FROM_VARIABLE is not monotonically increasing at index 2
I suspect that this is what you want:
file/var=zed zaxis.dat
let depth = (-1)*zed
define axis/z/depth/from_data/units=meters zax = depth
Your zed values are all negative but defined from the sea surface toward the bottom. That makes the values decreasing rather than increasing.
On the other hand, when we talk about "depth", it is normally positive and increasing toward the bottom. My definition of zax above conforms to this convention.
Cheers,
Ryo