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Self-contained runnable sample code for basic mesh plotting. #5501

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Self-contained runnable sample code for basic mesh plotting. #5501

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79 changes: 37 additions & 42 deletions docs/src/further_topics/ugrid/operations.rst
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Expand Up @@ -483,16 +483,32 @@ earlier:

.. code-block:: python

>>> import iris
>>> from iris.experimental.ugrid import PARSE_UGRID_ON_LOAD
>>>
>>> from geovista import GeoPlotter, Transform
>>> from geovista.common import to_xyz


# We'll re-use this to plot some real global data later.
>>> from geovista.common import to_cartesian as to_xyz
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@bjlittle bjlittle Sep 15, 2023 •
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Really?

You should adopt the use of to_cartesian and not rebrand it. The reason why you're doing this is already lost in the mists of time, and it's not recommending a good pattern to adopt to the reader moving forwards 👎

>>>
>>> testdata_path = iris.sample_data_path("mesh_C4_synthetic_float.nc")
>>> with PARSE_UGRID_ON_LOAD.context():
... cube = iris.load_cube(testdata_path)
...
>>> print(cube)
synthetic / (1) (-- : 96)
Mesh coordinates:
latitude x
longitude x
Mesh:
name Topology data of 2D unstructured mesh
location face
Attributes:
NCO 'netCDF Operators version 4.7.5 (Homepage = http://nco.sf.net, Code = h ...'
history 'Mon Apr 12 01:44:41 2021: ncap2 -s synthetic=float(synthetic) mesh_C4_synthetic.nc ...'
nco_openmp_thread_number 1
>>> def cube_faces_to_polydata(cube):
... lons, lats = cube.mesh.node_coords
... face_node = cube.mesh.face_node_connectivity
... indices = face_node.indices_by_location()
...
... mesh = Transform.from_unstructured(
... lons.points,
... lats.points,
Expand All @@ -502,50 +518,29 @@ earlier:
... start_index=face_node.start_index,
... )
... return mesh

>>> print(face_cube)
face_data / (K) (-- : 2; height: 3)
Dimension coordinates:
height - x
Mesh coordinates:
latitude x -
longitude x -
Attributes:
Conventions 'CF-1.7'

# Convert our mesh+data to a PolyData object.
# Just plotting a single height level.
>>> face_polydata = cube_faces_to_polydata(face_cube[:, 0])
...
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@bjlittle bjlittle Sep 15, 2023 •
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@pp-mo You can now simplify the call to Transform.from_unstructured as follows:

mesh = Transform.from_unstructured(
    lons.points,
    lats.points,
    connectivity=indices,
    data=cube.data,
    name=f"{cube.name()} / {cube.units}",
)

There is now no need to provide the start_index as geovista will detect this, and it's better to name the indices with the connectivity kwarg for clarity.

This is just a suggestion, and not strictly necessary.

>>> face_polydata = cube_faces_to_polydata(cube)
>>> print(face_polydata)
PolyData (0x7ff4861ff4c0)
N Cells: 2
N Points: 5
X Bounds: 9.903e-01, 1.000e+00
Y Bounds: 0.000e+00, 1.392e-01
Z Bounds: 6.123e-17, 5.234e-02
N Arrays: 2

# Create the GeoVista plotter and add our mesh+data to it.
PolyData (0x7f179a6b2800)
N Cells: 96
N Points: 98
N Strips: 0
X Bounds: -1.000e+00, 1.000e+00
Y Bounds: -1.000e+00, 1.000e+00
Z Bounds: -1.000e+00, 1.000e+00
N Arrays: 4
>>>
>>> my_plotter = GeoPlotter()
>>> my_plotter.add_coastlines(color="black")
>>> my_plotter.add_base_layer(color="grey")
>>> my_plotter.add_mesh(face_polydata)

# Centre the camera on the data.
>>> camera_region = to_xyz(
... face_cube.coord("longitude").points,
... face_cube.coord("latitude").points,
... radius=3,
... )
>>> camera_pos = camera_region.mean(axis=0)
>>> my_plotter.camera.position = camera_pos

>>> my_plotter.background_color = "#502020ff"
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@bjlittle bjlittle Sep 15, 2023 •
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If you use import geovista.theme there's need to set the background_color

>>> _ = my_plotter.add_coastlines(color="white", radius=1.01)
>>> _ = my_plotter.add_mesh(face_polydata, radius=1.0)
Comment on lines +535 to +536
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There's no real need here to set the radius, it's not adding anything of great value to "basic" plotting... it's just a distraction.

If you're concern is that the mesh is so low resolution that it's markedly different from the spherical coastlines, then only specify the radius for the coastlines. Setting the radius=1.0 for the face_polydata is a nop.

>>>
>>> my_plotter.show()

.. image:: images/plotting_basic.png
:alt: A GeoVista plot of the basic example Mesh.

This artificial data makes West Africa rather chilly!
This artificial data is very low resolution !

Here's another example using a global cubed-sphere data set:

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