Main Content

isonormals

Compute normals of isosurface vertices

Syntax

n = isonormals(X,Y,Z,V,vertices)
n = isonormals(V,vertices)
n = isonormals(V,p)
n = isonormals(X,Y,Z,V,p)
n = isonormals(...,'negate')
isonormals(V,p)
isonormals(X,Y,Z,V,p)

Description

n = isonormals(X,Y,Z,V,vertices) computes the normals of the isosurface vertices from the vertex list, vertices, using the gradient of the data V. The arrays X, Y, and Z define the coordinates for the volume V. The computed normals are returned in n.

n = isonormals(V,vertices) assumes the arrays X, Y, and Z are defined as [X,Y,Z] = meshgrid(1:n,1:m,1:p) where [m,n,p] = size(V).

n = isonormals(V,p) and n = isonormals(X,Y,Z,V,p) compute normals from the vertices of the patch identified by the handle p.

n = isonormals(...,'negate') negates (reverses the direction of) the normals.

isonormals(V,p) and isonormals(X,Y,Z,V,p) set the VertexNormals property of the patch identified by the handle p to the computed normals rather than returning the values.

Examples

collapse all

Compare the effect of different surface normals on the visual appearance of lit isosurfaces. In one case, the triangles used to draw the isosurface define the normals. In the other, the isonormals function uses the volume data to calculate the vertex normals based on the gradient of the data points. The latter approach generally produces a smoother-appearing isosurface.

Define a 3-D array of volume data.

data = cat(3,[0 .2 0; 0 .3 0; 0 0 0],...
    [.1 .2 0; 0 1 0; .2 .7 0],...
    [0 .4 .2; .2 .4 0;.1 .1 0]);
data = interp3(data,3,'cubic');

Draw an isosurface from the volume data and add lights. This isosurface uses triangle normals.

tiledlayout(1,2)
nexttile
fv = isosurface(data,.5);
p1 = patch(fv,'FaceColor','red','EdgeColor','none');
view(3)
daspect([1,1,1])
axis tight
camlight
camlight(-80,-10)
lighting gouraud
title('Triangle Normals')

Figure contains an axes object. The axes object with title Triangle Normals contains an object of type patch.

Draw the same lit isosurface using normals calculated from the volume data.

nexttile
fv = isosurface(data,.5);
p2 = patch(fv,'FaceColor','red','EdgeColor','none');
isonormals(data,p2)
view(3) 
daspect([1 1 1])
axis tight
camlight 
camlight(-80,-10) 
lighting gouraud
title('Data Normals')

Figure contains 2 axes objects. Axes object 1 with title Triangle Normals contains an object of type patch. Axes object 2 with title Data Normals contains an object of type patch.

These isosurfaces illustrate the difference between triangle and data normals.

Extended Capabilities

Version History

Introduced before R2006a