Per-tile transforms

[pjcozzi]

Fixes #98.

See

• Coordinate System and Units
• Tile transform
• External Tilesets

The new figures will be updated later for consistency with the rest of the spec.

[lilleyse]

I think a recursive example may be easier to grasp here for most readers.

[pjcozzi]

Ah, yes, it is much shorter. If you have a Cesium unit test handy, could you quickly run this?

[pjcozzi]

It is here: f557f56

[lilleyse]

Wow this covers a lot of small but important cases. Looks good to me!

[lilleyse]

Had to make two edits. Here's the working code.

        function computeTransforms(tileset) {
            var t = tileset.root;
            var transformToRoot = defined(t.transform) ? Matrix4.fromArray(t.transform) : Matrix4.IDENTITY;

            computeTransform(t, transformToRoot);
        }

        function computeTransform(tile, transformToRoot) {
            // Apply 4x4 transformToRoot to this tile's positions and bounding volumes

            var inverseTransform = Matrix4.inverse(transformToRoot, new Matrix4());
            var normalTransform = Matrix4.getRotation(inverseTransform, new Matrix3());
            normalTransform = Matrix3.transpose(normalTransform, normalTransform);
            // Apply 3x3 normalTransform to this tile's normals

            var children = tile.children;
            var length = children.length;
            for (var k = 0; k < length; ++k) {
                var child = children[k];
                var childToRoot = defined(child.transform) ? Matrix4.fromArray(child.transform) : Matrix4.clone(Matrix4.IDENTITY);
                childToRoot = Matrix4.multiplyTransformation(transformToRoot, childToRoot, childToRoot);
                computeTransform(child, childToRoot);
            }
        }

[lilleyse]

I'll just commit the change.

[pjcozzi]

Thanks @lilleyse! Is this ready?

Does the spec need to cover anything else based on your implementation experience?

[lilleyse]

It covers everything I can think of.