Open GoogleCodeExporter opened 8 years ago
That's quit easy. The total area of a mesh's outer surface is the sum of the
area of all the triangles. If a facet have more than 3 vertices, we just break
it up following the triangle fan splitting princeple. The area of each
triangle can be computed using the cross product of the edge vectors.
I used to write an unoptimized implementation of this for someone. Just add the
following function to your code:
function calculateOuterSufaceArea(mesh) {
var area = 0;
var ibuf = mesh.indexBuffer;
var vbuf = mesh.vertexBuffer;
// walk through all faces, summing up the surface area
var i=0, j=0;
while (i < mesh.faceCount) {
var v0, v1, v2;
var x0, y0, z0, x1, y1, z1, x2, y2, z2;
var dx1, dy1, dz1, dx2, dy2, dz2;
var cpx, cpy, cpz;
v0 = ibuf[j++] * 3;
v1 = ibuf[j++] * 3;
// calculate the area of this face
do {
v2 = ibuf[j++] * 3;
x0 = vbuf[v0 ];
y0 = vbuf[v0 + 1];
z0 = vbuf[v0 + 2];
x1 = vbuf[v1 ];
y1 = vbuf[v1 + 1];
z1 = vbuf[v1 + 2];
x2 = vbuf[v2 ];
y2 = vbuf[v2 + 1];
z2 = vbuf[v2 + 2];
dx1 = x1 - x0;
dy1 = y1 - y0;
dz1 = z1 - z0;
dx2 = x2 - x0;
dy2 = y2 - y0;
dz2 = z2 - z0;
cpx = dy1 * dz2 - dz1 * dy2;
cpy = dz1 * dx2 - dx1 * dz2;
cpz = dx1 * dy2 - dy1 * dx2;
area += Math.sqrt(cpx*cpx + cpy*cpy + cpz*cpz);
v1 = v2;
} while (ibuf[j] >= 0);
// continue to next face
j++;
i++;
}
return 0.5 * area;
}
The function can be used like this:
// output the surface area of the first mesh after a model is loaded completely
var mesh = viewer.getScene().getChildren()[0];
console.info('surface area = ' + calculateOuterSufaceArea(mesh));
In most cases, your model may consist of more than one mesh. To calculate the
total surface area:
// compute and output the total surface area of a whole model after it has been loaded completely
var totalArea = 0;
viewer.getScene().forEachChild( function(mesh) {
totalArea += calculateOuterSufaceArea(mesh);
};
console.info('total area = ' + totalArea);
That's it.
Original comment by Humu2...@gmail.com
on 24 Sep 2014 at 4:13
Thank you, Thank you, Thank you my friend.
SAVED MY LIFE.
The world would be a better place if we had more people like you.
Best regards,
Alberto.
Original comment by andrad...@gmail.com
on 24 Sep 2014 at 8:04
Original issue reported on code.google.com by
andrad...@gmail.com
on 24 Sep 2014 at 2:55