Granular.jl

commit 809cebdad423f7a7109fa9139f871c595df1ea16
parent 23b5df397b0b3d2d7619da5e4672675bc3474e90
Author: Anders Damsgaard <andersd@riseup.net>
Date:   Fri, 21 Apr 2017 17:20:25 -0400

add bilinear interpolation scheme for Arakawa A grids

Diffstat:
M
src/grid.jl
 | 
31
+++++++++++++++++++++++++++++++

1 file changed, 31 insertions(+), 0 deletions(-)
diff --git a/src/grid.jl b/src/grid.jl
@@ -27,3 +27,34 @@ function fitWorldSize(margin::vector = zeros(3))
     g_world_size[:] = maxpos[:] + margin[:]
 end
 
+"""
+Use bilinear interpolation to interpolate a staggered grid to an arbitrary 
+position in a cell.  Assumes north-east convention, i.e. (i,j) is located at the 
+north-east corner.
+
+# Arguments
+* `field::Array{Float64, 4}`: a scalar field to interpolate from
+* `xi::float`: relative x position in cell [-], must be in `[0., 1.]`
+* `yj::float`: relative y position in cell [-], must be in `[0., 1.]`
+* `i::Int`: i-index of cell containing point
+* `j::Int`: j-index of cell containing point
+* `grid_type::String="Arakawa A"`: grid system for `field`
+"""
+function bilinearInterpolation(field::Array{Float64, 4},
+                               xi::float,
+                               yj::float,
+                               i::Int,
+                               j::Int;
+                               grid_type::String="Arakawa A")
+
+    if xi < 0. || xi > 1. || yj < 0. || yj > 1.
+        error("relative coordinates outside bounds ($(xi), $(yj))")
+    end
+
+    if grid_type == "Arakawa A"
+        return (field[i,j]*xi + field[i-1,j]*(1. - xi))*yi +
+            (field[i,j-1]*xi + field[i-1,j-1]*(1. - xi))*(1. - yi)
+    else
+        error("grid type not understood.")
+    end
+end