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Psvelo [Plot velocity vectors, crosses, and wedges] #510
Description
Description of the desired feature
Implementation of the psvelo function.
It would be really a great feature for pygmt to be able to plot velocity vectors and confidence ellipse, because, at the moment, it is not possible with the classic matplotlib function quiver.
Example plots
Two examples are available on gmt.soest.hawaii.edu. I copy the description of the example provide and the output when I run the code on GMT-6.0.0.
Example 1
"The following should make big red arrows with green ellipses outlined in red. Note that the 39% confidence scaling will give an ellipse which fits inside a rectangle of dimension Esig by Nsig."
gmt psvelo << END -h2 -R-10/10/-10/10 -W0.25p,red -Ggreen -L -Se0.2/0.39/18 \
-B1g1 -Jx0.4/0.4 -A0.3p -P -V > test.ps
#Long. Lat. Evel Nvel Esig Nsig CorEN SITE
#(deg) (deg) (mm/yr) (mm/yr)
0. -8. 0.0 0.0 4.0 6.0 0.500 4x6
-8. 5. 3.0 3.0 0.0 0.0 0.500 3x3
0. 0. 4.0 6.0 4.0 6.0 0.500
-5. -5. 6.0 4.0 6.0 4.0 0.500 6x4
5. 0. -6.0 4.0 6.0 4.0 -0.500 -6x4
0. -5. 6.0 -4.0 6.0 4.0 -0.500 6x-4
END
The example above seems to be running fine on GMT-6.0.0, except that the colour of my ellipses are not green.
Example 2
"This example should plot some residual rates of rotation in the Western Transverse Ranges, California. The wedges will be dark gray, with light gray wedges to represent the 2-sigma uncertainties."
gmt psvelo << END -Sw0.4/1.e7 -W0.75p -Gdarkgray -Elightgray -h1 -D2 -Jm2.2 \
-R240./243./32.5/34.75 -Bf10ma60m/WeSn -P > test.ps
#lon lat spin(rad/yr) spin_sigma (rad/yr)
241.4806 34.2073 5.65E-08 1.17E-08
241.6024 34.4468 -4.85E-08 1.85E-08
241.0952 34.4079 4.46E-09 3.07E-08
241.2542 34.2581 1.28E-07 1.59E-08
242.0593 34.0773 -6.62E-08 1.74E-08
241.0553 34.5369 -2.38E-07 4.27E-08
241.1993 33.1894 -2.99E-10 7.64E-09
241.1084 34.2565 2.17E-08 3.53E-08
END
*I don't really understand what should be plotted here [I am a physical oceanographer], but it doesn't seem absurd...
Are you willing to help implement and maintain this feature?
I can try to help but I am not an expert in gmt or in python programming ... Therefore I will need some help to understand how complex functions are coded :-D
Activity
weiji14 commentedon Jul 12, 2020
Hi @lhoupert, it's called velo now 😉. Do you have an example of how it looks like? You can edit the original post with an example figure. I've not personally used
velobefore but there's certainly been interest in wrapping some of the supplementary modules (see e.g. #516).Considering that
velois quite similar toplot, except for the-Sflag, a quick way to start might just be to:plotcode at https://github.com/GenericMappingTools/pygmt/blob/master/pygmt/base_plotting.py#L447 and rename it tovelo.-Sflag somehow.If you're keen, open up a Pull Request and give it a go! it'll be easier for us or someone else to pick up the PR and add things like gallery examples and unit tests. It might be useful to see how
plot3dis being implemented at #471.lhoupert commentedon Jul 13, 2020
Thank you @weiji14 . It is exactly the
-Sflag options that interest me :-). Any suggestion on how to do implement it?I added two example pictures in the original post.
Also, I just started editing the documentation string and looked into the code copied from
plotbut I don't know how to handle the fact thattableis a required argument forvelowhile it is only optional forplot. Do you know how I should write this down?weiji14 commentedon Jul 13, 2020
Thanks for adding the example, it's nice having a visual image on what we're working towards 😄 After taking a closer look, I think the
-Soption invelocould be implemented almost exactly likeplot(i.e. you could just copy and paste it), though it is a required argument invelo. It would just take in astr(e.g.S="e0.2/0.39/18"), and that would handle the differenttablecolumns being passed in.We'll always require some form of data input (e.g. longitude, latitude, etc), even for PyGMT's
plot. Any 'required' or 'optional' argument is just an 'argument' to us! Inplot, we have two options to pass in data:x=0, y=1, style="c"), good for plotting a single or a few points.data(e.g.data=df), good for plotting several rows of dataAgain, I imagine this would be very similar for
velo, and I wouldn't be surprised if everything works if you just copied and pasted thedef plotcode and renamed this line tovelo:pygmt/pygmt/base_plotting.py
Line 559 in 0f12972
I see you've already made a fork for PyGMT, if you already have something done, just open up a draft pull request and we (and the PyGMT team) can work on it together, will be much easier to suggest changes and talk about the specifics.
lhoupert commentedon Jul 14, 2020
Thank you @weiji14 for the help. I started working on it and I opened a pull request [here].