InterpFromMeshToGrid

loganemann

Hello,
I'm trying to interpolate a velocity field from a triangle mesh to a grid. I'm running the most recent version of ISSM on a linux machine. Looking at the function's code, the syntax is:

`InterpFromMeshToGrid(index,x,y,data,xgrid,ygrid,default_value),`

I think I've figured out what to use for each input except xgrid and ygrid. The description of this variable is 'parameters that define the grid'. I figure it is most likely min and max values for x and y, number of grid spaces, etc, but I'm unsure how to input this data.

I found an old forum post from 2014 (https://issm.ess.uci.edu/forum/d/64-interpolation) that describes how to use the function from an older release, but the syntax for this function is different, instead specifying,

InterpFromMeshToGrid(index,x,y,data,xmin,ymax,xposting,yposting,nlines,ncols,default_value)

with the example of
InterpFromMeshToGrid(md.mesh.elements,md.mesh.x,md.mesh.y,md.inversion.vx_obs,min(md.mesh.x),max(md.mesh.y),100,100,(max(md.mesh.y)-min(md.mesh.y))/100,(max(md.mesh.x)-min(md.mesh.x))/100,NaN);

I assume that in the most recent release xgrid and ygrid are either some array or data structure that contain xmin, ymax, xposting, yposting, nlines, and ncols.

Thanks,
Logan

mathieumorlighem

Hi Logan,

The new version of InterpFromMeshToGrid is a lot simpler because you do not need to figure out how big your grid is.

Let's say you want a grid that coincides with your mesh at a resolution of 1.5 km. You would do this:

VEL=InterpFromMeshToGrid(md.mesh.elements,md.mesh.x,md.mesh.y,md.inversion.vel_obs,min(md.mesh.x):1.5e3:max(md.mesh.x),min(md.mesh.y):1.5e3:max(md.mesh.y),NaN);

I hope this helps
Mathieu

loganemann

Thanks for the quick reply! It works great!

-Logan