pyGMT makecpt error: CPT <stdin> has no z-slices!

Q&A PyGMT Q&A
1

Hi,

I’d like to invert a (built-in) colour map. I adapted a code from another thread (pyGMT makecpt - background and foreground) to arrive at:
pygmt.makecpt(cmap = "devon", reverse = True, series = [0, 7000, 10], output="devon_r.cpt", continuous = True, M = True)
I have also tried M=" " and running without series=[]

However, when I use this colourmap to plot something, it does plot the colourmap correctly inverted, but no colourbar below the map, and pyGMT returns the error colorbar [ERROR]: CPT <stdin> has no z-slices!.

I have tried the pyGMT manual and tutorials but I have not been able to identify the problem in my code.

Many thanks!!
Thomas

2

I’m not sure how it works with python, but do you ask for the colorbar to be plotted while specifying the cpt’s name?

3

Hello! I have the same question when I plot the puctures using the GMT ,have you solved the problem ?

4

Please open a separate post and show your script so that we can see what’s happening.

5

Hello,when I use the seis and polar scale, I get an error like “makecpt: Error: CPT polar.cpt has no z-slices!” May I ask why this is and how to solve it

6

It just likes below
[zhongen@localhost gmtplot]$ gmt makecpt -Cpolar -T3/4/0.3 -I -Z > seis.cpt
makecpt: Error: CPT polar.cpt has no z-slices!
[Session gmt (0)]: Error returned from GMT API: GMT_CPT_READ_ERROR (8)
[Session gmt (0)]: Error returned from GMT API: GMT_CPT_READ_ERROR (8)
[Session gmt (0)]: Error returned from GMT API: GMT_CPT_READ_ERROR (8)

7

The command works well for me.

8

So could it be the version ？

9

So could it be the version？

10

No.

But a broken installation maybe.

11

OK，thank you for your reply. I’ll try to install it again

12

Just a short comment on this conversation:

In the first post (pyGMT makecpt error: CPT <stdin> has no z-slices!), the error
colorbar [ERROR]: CPT <stdin> has no z-slices!
is reported.

Now we have (pyGMT makecpt error: CPT <stdin> has no z-slices! - #6 by yangxuan) the error
makecpt: Error: CPT polar.cpt has no z-slices!

Also we are jumping from PyGMT to GMT.

The first error occurs, if users save their colormap first to a file via the output parameter of pygmt.makecpt and later use cmap=True within Figure.colorbar. This does not work. If you save your colormap to a file you have to pass the used filename to cmap of Figure.colorbar:

import pygmt

size = 5

fig = pygmt.Figure()
fig.basemap(region=[-size, size, -size, size], projection=f"X{size*2}c", frame=True)

pygmt.makecpt(cmap="polar", series=[0, 10, 1], output="polar_test.cpt")
# colormap is saved to a file via the "output" parameter

# fig.colorbar(cmap=True)  # fails with
# colorbar [ERROR]: CPT <stdin> has no z-slices!
# [Session pygmt-session (33)]: Error returned from GMT API: GMT_CPT_READ_ERROR (8)
# [Session pygmt-session (33)]: Error returned from GMT API: GMT_CPT_READ_ERROR (8)

fig.colorbar(cmap="polar_test.cpt") # works
# Users need to pass the filename of the colormap if the created colormap was saved to a file

fig.show()

For the second issue in GMT, I feel we need your GMT script and it makes sense to start a separate topic as already mentioned by @seisman :slightly_smiling_face: .