Converting a GeoTIFF to an unprojected lat/lon grid?

Hello, I would like to plot a GeoTIFF with the function surfacem.

Using

[A,cmap,R] = geotiffread(filin);

I get a 448 x 304 matrix, A, and the MapCellsReference object, R.

Additionally, I know that I can use

info = geotiffinfo(filin);
[x,y] = pix2map(R, 1, 1);
[lat,lon] = projinv(info, x, y)

to get single point lats and longs.

How would I convert the entire file to a grid? x and y need to be the same size, but the dimensions of A are not the same size. Thanks!