Fix connected theta edges for plot3d

[YigitElma]

Currently, if you don't give a full theta grid to plot_3d, it will connect the theta edges and end up this kind of plots,

I don't know about you, but I want it to behave like this,

[YigitElma]

Here is the code to generate this plot,

import plotly.graph_objects as go
from desc.grid import LinearGrid
from desc.plotting import plot_3d
import numpy as np

fig = go.Figure()
for r in [0.3, 0.6, 1]:
    grid = LinearGrid(
        rho=r,
        theta=np.linspace(0, 2 * np.pi, 200),
        zeta=np.linspace(0, 2 * np.pi/eq.NFP, 200),
        sym=True,
    )
    plot_3d(eq, "|B|", grid=grid, fig=fig)
fig.show()

[github-actions]

|             benchmark_name             |         dt(%)          |         dt(s)          |        t_new(s)        |        t_old(s)        | 
| -------------------------------------- | ---------------------- | ---------------------- | ---------------------- | ---------------------- |
 test_build_transform_fft_lowres         |     +0.46 +/- 6.48     | +2.40e-03 +/- 3.38e-02 |  5.24e-01 +/- 2.3e-02  |  5.22e-01 +/- 2.5e-02  |
 test_equilibrium_init_medres            |     -0.37 +/- 1.06     | -1.55e-02 +/- 4.41e-02 |  4.14e+00 +/- 2.9e-02  |  4.15e+00 +/- 3.3e-02  |
 test_equilibrium_init_highres           |     -0.05 +/- 2.09     | -2.90e-03 +/- 1.15e-01 |  5.49e+00 +/- 6.0e-02  |  5.49e+00 +/- 9.8e-02  |
 test_objective_compile_dshape_current   |     -0.17 +/- 0.79     | -6.41e-03 +/- 3.02e-02 |  3.83e+00 +/- 1.5e-02  |  3.83e+00 +/- 2.6e-02  |
 test_objective_compute_dshape_current   |     +0.13 +/- 2.24     | +4.29e-06 +/- 7.69e-05 |  3.43e-03 +/- 6.4e-05  |  3.43e-03 +/- 4.3e-05  |
 test_objective_jac_dshape_current       |     -1.05 +/- 7.03     | -4.26e-04 +/- 2.85e-03 |  4.01e-02 +/- 1.6e-03  |  4.06e-02 +/- 2.4e-03  |
 test_perturb_2                          |     -0.30 +/- 2.18     | -5.28e-02 +/- 3.79e-01 |  1.74e+01 +/- 1.2e-01  |  1.74e+01 +/- 3.6e-01  |
 test_proximal_freeb_jac                 |     +0.49 +/- 1.35     | +3.67e-02 +/- 1.01e-01 |  7.52e+00 +/- 9.7e-02  |  7.48e+00 +/- 2.5e-02  |
 test_solve_fixed_iter                   |     -0.13 +/- 60.08    | -6.64e-03 +/- 2.96e+00 |  4.93e+00 +/- 2.1e+00  |  4.93e+00 +/- 2.1e+00  |
 test_build_transform_fft_midres         |     -0.02 +/- 3.25     | -9.48e-05 +/- 1.96e-02 |  6.02e-01 +/- 1.8e-02  |  6.02e-01 +/- 7.5e-03  |
 test_build_transform_fft_highres        |     -0.35 +/- 1.69     | -3.48e-03 +/- 1.68e-02 |  9.93e-01 +/- 8.9e-03  |  9.97e-01 +/- 1.4e-02  |
 test_equilibrium_init_lowres            |     -1.76 +/- 3.62     | -6.79e-02 +/- 1.40e-01 |  3.79e+00 +/- 1.8e-02  |  3.86e+00 +/- 1.4e-01  |
 test_objective_compile_atf              |     -0.04 +/- 4.81     | -3.23e-03 +/- 3.78e-01 |  7.86e+00 +/- 2.4e-01  |  7.87e+00 +/- 2.9e-01  |
 test_objective_compute_atf              |     +1.17 +/- 3.95     | +1.21e-04 +/- 4.06e-04 |  1.04e-02 +/- 2.6e-04  |  1.03e-02 +/- 3.2e-04  |
 test_objective_jac_atf                  |     -0.93 +/- 4.99     | -1.81e-02 +/- 9.66e-02 |  1.92e+00 +/- 8.9e-02  |  1.94e+00 +/- 3.7e-02  |
 test_perturb_1                          |     +0.64 +/- 4.86     | +8.16e-02 +/- 6.16e-01 |  1.27e+01 +/- 4.2e-01  |  1.27e+01 +/- 4.5e-01  |
 test_proximal_jac_atf                   |     -0.64 +/- 1.41     | -5.24e-02 +/- 1.16e-01 |  8.19e+00 +/- 7.4e-02  |  8.24e+00 +/- 8.9e-02  |
 test_proximal_freeb_compute             |     -0.80 +/- 0.96     | -1.48e-03 +/- 1.76e-03 |  1.82e-01 +/- 1.3e-03  |  1.84e-01 +/- 1.2e-03  |

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.31%. Comparing base (b683e85) to head (f1af4e2).
Report is 4 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1237      +/-   ##
==========================================
- Coverage   95.32%   95.31%   -0.02%     
==========================================
  Files          90       90              
  Lines       22713    22713              
==========================================
- Hits        21651    21648       -3     
- Misses       1062     1065       +3     

Files with missing lines	Coverage Δ
desc/plotting.py	95.66% <100.00%> (-0.08%)	⬇️

... and 2 files with indirect coverage changes

[f0uriest]

Does this still work correctly if the surface is closed?

[YigitElma]

Does this still work correctly if the surface is closed?

Those were also behaving well with this change. I can test again, it was really late when I tested it yesterday.

[YigitElma]

Does this still work correctly if the surface is closed?

Yes, it works, unless you specifically give a grid like this,

eq = get("ATF")
grid = LinearGrid(
        rho=1.,
        theta=np.linspace(0, 2 * np.pi, 200, endpoint=False),
        zeta=np.linspace(0, 2 * np.pi/eq.NFP, 200),
    )
plot_3d(eq, '|B|', grid=grid)

Because if you don't give a grid, the default grid created by _get_grid() function uses endpoint=True which inherently closes the surface.