.to_raster() options?

[zmoon]

Since .to_raster()¹ doesn't expose any options, it seems that currently the only way to make it try harder and produce a sharper image (assuming you have high-resolution data) is to set the figure DPI to something higher than the default (100) before calling .to_raster(). This is a bit annoying if you're using Jupyter though, because unless you reset the figure DPI to the default afterwards, it will display the figure blown up.

Anyway, I feel like this method should at least be mentioned in https://uxarray.readthedocs.io/en/latest/user-guide/mpl.html#rasterization. And/or option(s) could be added to .to_raster().

Footnotes

1. thanks for adding this, have been enjoying it ↩

[philipc2]

Hi @zmoon

Thanks for the feedback! We've implemented to_raster() in a way that uses the pixels from the provided GeoAxes to sample the underlying grid. The projected screens-space pixels are converted to normalized cartesian coordinates and sampled internally to see which cell they lie within.

You should be able to set the DPI when creating the figure, which would only apply to that one without affecting others.

fig, ax = plt.subplots(
    figsize=(5, 10),
    dpi=150,  # set DPI for the current figure 
    subplot_kw={"projection": ccrs.PlateCarree()}, constrained_layout=True
)

I can't immediately think of a way to produce sharper images without blowing up the image. With our naitive plotting API (using HoloViews/Datashader), the pixel ratio parameter is used to control the effective resolution.

Pinging @kafitzgerald and @anissa111 since they have done more work with MPL than I have, so they might know a better approach.

I do like the idea of adding some context in the user guide notebook.

[zmoon]

As a user, we can do it like this:

pixel_ratio = 2
fig = plt.figure(dpi=100 * pixel_ratio)
# ... rasterize ...
fig.set_dpi(100)

But you could also consider adding a pixel_ratio parameter to .to_raster(). Since you're just making a meshgrid, should be easy to apply a scalar to nx and ny?

[zmoon]

I do like the idea of adding some context in the user guide notebook.

As part of this, I think the uxarray docs could talk about pixel_ratio somewhere. It's used in two example notebooks but never mentioned. ¹

Footnotes

1. It's mentioned in multiple places in the Pythia cookbook, e.g. here, but not everyone finds that. ↩

[zmoon]

adding a pixel_ratio parameter to .to_raster()

Tried it out.

Any interest in PR for this?

[philipc2]

This looks great! Feel free to open up a PR for this.