Horizontal swimming?

[brucelaughlin]

I'd like to add shoreward swimming to a custom model. In its simplest form, it would just be movement in a fixed direction at each timestep. In an ideal form, "larvae" would be able to swim towards the nearest shore (including island coastlines).

For the simple version (movement in a fixed direction), I think this can be accomplished in a way similar to how it's done in "larvae_vertical_migration()", within "larvalfish.py()".

The more complicated version, which requires particles to be aware of the direction to the nearest coastline (including islands), seems much harder. Would this be prohibitively difficult? If not, where might I start? A new method, which access grid information and uses current particle locations to find the nearest grid point that is land?