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C++ API

Function File: [n] = isonormals (val, v)
Function File: [n] = isonormals (val, p)
Function File: [n] = isonormals (x, y, z, val, v)
Function File: [n] = isonormals (x, y, z, val, p)
Function File: [n] = isonormals (…, "negate")
Function File: isonormals (…, p)

Calculate normals to an isosurface.

If called with one output argument and the first input argument val is a three-dimensional array that contains the data for an isosurface geometry and the second input argument v keeps the vertices of an isosurface then return the normals n in form of a matrix with the same size than v at computed points [x, y, z] = meshgrid (1:l, 1:m, 1:n). The output argument n can be taken to manually set VertexNormals of a patch.

If called with further input arguments x, y and z which are three–dimensional arrays with the same size than val then the volume data is taken at those given points. Instead of the vertices data v a patch handle p can be passed to this function.

If given the string input argument "negate" as last input argument then compute the reverse vector normals of an isosurface geometry.

If no output argument is given then directly redraw the patch that is given by the patch handle p.

For example: 

function [] = isofinish (p)
  set (gca, "PlotBoxAspectRatioMode", "manual", ...
            "PlotBoxAspectRatio", [1 1 1]);
  set (p, "VertexNormals", -get (p,"VertexNormals")); # Revert normals
  set (p, "FaceColor", "interp");
  ## set (p, "FaceLighting", "phong");
  ## light ("Position", [1 1 5]); # Available with JHandles
endfunction

N = 15;    # Increase number of vertices in each direction
iso = .4;  # Change isovalue to .1 to display a sphere
lin = linspace (0, 2, N);
[x, y, z] = meshgrid (lin, lin, lin);
c = abs ((x-.5).^2 + (y-.5).^2 + (z-.5).^2);
figure (); # Open another figure window

subplot (2,2,1); view (-38, 20);
[f, v, cdat] = isosurface (x, y, z, c, iso, y);
p = patch ("Faces", f, "Vertices", v, "FaceVertexCData", cdat, ...
           "FaceColor", "interp", "EdgeColor", "none");
isofinish (p);  # Call user function isofinish

subplot (2,2,2); view (-38, 20);
p = patch ("Faces", f, "Vertices", v, "FaceVertexCData", cdat, ...
           "FaceColor", "interp", "EdgeColor", "none");
isonormals (x, y, z, c, p); # Directly modify patch
isofinish (p);

subplot (2,2,3); view (-38, 20);
p = patch ("Faces", f, "Vertices", v, "FaceVertexCData", cdat, ...
           "FaceColor", "interp", "EdgeColor", "none");
n = isonormals (x, y, z, c, v); # Compute normals of isosurface
set (p, "VertexNormals", n);    # Manually set vertex normals
isofinish (p);

subplot (2,2,4); view (-38, 20);
p = patch ("Faces", f, "Vertices", v, "FaceVertexCData", cdat, ...
           "FaceColor", "interp", "EdgeColor", "none");
isonormals (x, y, z, c, v, "negate"); # Use reverse directly
isofinish (p);

See also: isosurface, isocolors.

Package: octave