Update elevation script to use cell_id structure

[lelavathy]

This update modifies the Maliau elevation preprocessing script so that the
output dataset follows the Virtual Ecosystem (VE) spatial data structure and
addresses the issue reported in “Input data is flipped when mapped on grid
#1054” #1054

Key changes include:

Replacing the 2D spatial dimensions (x, y) with a single cell_id
dimension consistent with VE grid structure.

Flattening the elevation grid using row-major ordering with a top-left
origin (cell_id = 0 at the top-left cell).

Explicitly controlling the orientation of the y-axis to prevent the grid
from being flipped when mapped to VE cells.

Storing per-cell spatial coordinates (x, y, and UTM coordinates) so
that each cell_id can be correctly mapped back to its spatial position.

These changes ensure that the elevation dataset aligns with the VE grid
layout and prevent the input data from being vertically flipped when mapped
onto the simulation grid.

[davidorme]

I very strongly recommend not doing this. This is a VE model coding problem. I completely understand that the result is annoying to deal with and you get the flipped outputs, but let us fix the problem in the model.

That fix isn't going to happen immediately, but changing the inputs makes them harder to visualise and it is much harder to debug potential issues with cell_id coding. Stick with XY and let us make it work from the model end.

[annarallings]

Could we maybe put this as an issue in the VE repo? Something to tackle later (if it isn't already in there)

[davidorme]

Could we maybe put this as an issue in the VE repo? Something to tackle later (if it isn't already in there)

It's there: ImperialCollegeLondon/virtual_ecosystem#1054