`interp2`

Interpolation of data on a 2-D grid.

Syntax

Vq = interp2(X, Y, V, Xq, Yq)

Linear interpolation of V sampled on the grid (X,Y) at the points (Xq,Yq).

Vq = interp2(V, Xq, Yq)

Assumes the grid is 1:n by 1:m, the column and row indices of V.

Vq = interp2(..., method, extrapval)

Selects the method ('linear', 'nearest', 'cubic', 'spline', 'makima') and a value for points outside the grid.

Description

interp2 works on data in meshgrid orientation, where the first index of V follows Y and the second follows X. The linear method is bilinear: it interpolates along one axis and then along the other inside each grid cell.

For grids in ndgrid orientation, or for more than two dimensions, use interpn.

Input arguments

X, Y: Grid coordinates as meshgrid arrays or as vectors (X along columns, Y along rows).
V: Matrix of values; V(i,j) belongs to (X(j), Y(i)).
Xq, Yq: Query coordinates. Vectors of equal shape are paired point by point.

Output arguments

Vq: Interpolated values. Points outside the grid give NaN unless extrapval is given.

Example

Bilinear and nearest lookups

[X, Y] = meshgrid(1:3);
V = X + 10*Y;
interp2(X, Y, V, 1.5, 2.5)
interp2(V, 1.5, 2.5)
interp2(X, Y, V, 1.5, 2.5, 'nearest')
interp2(X, Y, V, 4, 4, 'linear', 0)

Output

ans = 26.5000
ans = 26.5000
ans = 32
ans = 0

interp2