Gallery example to showcase blockmean/blockmedian and surface

[weiji14]

Description of the desired feature

As suggested by #1351 (comment), it would be great to have a gallery example (or a full tutorial) showing how to use blockmean/blockmedian to reduce an xyz table dataset, and then run surface on the output to produce a grid (that can be plotted). There is an old and outdated example for processing LIDAR points at https://github.com/GenericMappingTools/foss4g2019oceania/blob/v1/3_lidar_to_surface.ipynb that can be used as a starting guide.

A challenge might be in sourcing a suitable xyz dataset that is openly available for this gallery example. Anyone have any suitable ideas?

Are you willing to help implement and maintain this feature? Happy to review or guide someone to work on this

[maxrjones]

I used the xyz -> blockmedian -> surface workflow in the tutorial for the PyGMT refresher, which can also be used as a reference for this gallery example.