interp2 error: The grid vectors must be strictly monotonically increasing.

The error is that "the grid vector must be strictly monotonically increasing" I am confused by this, because the vector a1 and b1 is absolutely monotonic.

%% plot segment1 int=1; % interval of mesh method='nearest'; s1x=Segment1new(:,3); s1y=Segment1new(:,4); s1z=Segment1new(:,5);

mins1x=ceil(min(s1x)); maxs1x=fix(max(s1x)); mins1y=ceil(min(s1y)); maxs1y=fix(max(s1y));

a1=(mins1x:int:maxs1x); b1=(mins1y:int:maxs1y);

[S1X,S1Y]=meshgrid(a1,b1); %produce mesh grid S1Z=interp2(s1x,s1y,s1z,S1X,S1Y,method);%interpolate ZZ mesh(S1X,S1Y,S1Z) hold on

Answer 1

[Steven Lord]

The query points do not need to be strictly monotonically increasing. The points at which the data to be interpolated is specified do need to be strictly monotonically increasing.

% Generate sample data
[Xmono, Ymono] = meshgrid(-3:3, -3:3);
Xnon = Xmono(randperm(7), randperm(7));
Ynon = Ymono(randperm(7), randperm(7));
V = Xmono + Ymono;

% Interpolate using the monotonically increasing X and Y data as the first two inputs
Vq1Succeeds = interp2(Xmono, Ymono, V, Xnon, Ynon);
szVq1 = size(Vq1Succeeds)

% Interpolate using the non-monotonically increasing X and Y data as the first two inputs
Vq2Fails = interp2(Xnon, Ynon, V, Xmono, Ymono);
szVq2 = size(Vq2Fails)

To interpolate scattered data (data known at locations that don't lie on a grid) use scatteredInterpolant instead.