Control Faceting and Lighting in 3D DWF Files

For those of you working with the DWF Toolkit, did you know that you can control the number of bits used to represent 3D (x,y,z) values in your DWF output? DWF Software Architect, Garrick Evans, notes that you can specify the number of bits for the 3D geometry as well as the lighting normals. Larger numbers improve the fidelity of the resulting DWF file but also moderately increase its file size.

DWFModel::enableNormalsCompression( nTotalNormalBits );
DWFModel::enableVertexCompression( nTotalVertexBits, nTotalParameterBits );

The files below are named “Vert-n Norm-m.dwf” where n is the number of total bits used for vertex coordinate quantization (e.g. 54 bits / 3 dimensions = 18 bits per dimension) and m is the total number of bits used vertex normal vector quantization. Fewer bits means more compression but also less data and thus less accuracy. The last file, [54-24], is what the DWF Toolkit publishes by default.

Vertex	Normal	File Size (bytes)	File Name
18	24	10,226	Vert-18Norm-24.dwf
24	24	11,461	Vert-24Norm-24.dwf
30	24	12,707	Vert-30Norm-24.dwf
36	12	12,549	Vert-36Norm-12.dwf
36	15	13,164	Vert-36Norm-15.dwf
36	18	13,771	Vert-36Norm-18.dwf
36	21	14,403	Vert-36Norm-21.dwf
36	24	15,121	Vert-36Norm-24.dwf
42	24	17,027	Vert-42Norm-24.dwf
45	12	15,470	Vert-45Norm-12.dwf
45	15	16,157	Vert-45Norm-15.dwf
45	18	16,810	Vert-45Norm-18.dwf
45	21	17,434	Vert-45Norm-21.dwf
45	24	18,125	Vert-45Norm-24.dwf
48	12	17,334	Vert-48Norm-12.dwf
48	15	18,025	Vert-48Norm-15.dwf
48	18	18,692	Vert-48Norm-18.dwf
48	21	19,344	Vert-48Norm-21.dwf
48	24	20,098	Vert-48Norm-24.dwf
54	12	19,373	Vert-54Norm-12.dwf
54	15	20,102	Vert-54Norm-15.dwf
54	18	20,773	Vert-54Norm-18.dwf
54	21	21,447	Vert-54Norm-21.dwf
54	24	22,212	Vert-54Norm-24.dwf

For this particular case, the two ends of the spectrum are:

1. 
2. 

The second image has smoother geometry and more precise specular highlights. DWF Toolkit users can balance fidelity versus file size trade-offs suited to their own applications. Powerful programming capabilities for selecting how to represent 3D design data is another way DWF goes beyond 2D paper.