The file format is called "3DMF" (3-D Metafile), and it has both an ASCII (text) and a binary form. Dendrometer always uses the ASCII form. This means, with an appropriate text editor (I recommend BBEdit Lite), you can view and edit the source code.

A note about file types: Every Macintosh document has a Creator (the application that is launched when you double-click it), and a Type (identifies the type of data contained by the document). Like Dendrometer documents, ASCII-form 3DMF documents have a dual identity. If the type is TEXT, they will be read as text files, and most QuickDraw 3D viewers will not recognize them as containing three-dimensional graphics. If the type is 3DMF, they will be read by QuickDraw 3D viewers (including SimpleText and the Scrapbook), but they may not appear eligible to text editors. Some editors (including BBEdit Lite) can be told to show all files; this will allow you to edit a 3DMF file without changing its file type or creator. If you find you need to change the file type but don't know how, write to me; there are a variety of ways to do this.

3DMetafile ( 1 0 Stream Label0> )
# Exported from Dendrometer
Cylinder (94 48 2 -3 7 0 0 0 8 9 10 8 )
Cylinder (19 113 -5 -6 1 0 0 0 6 103 58 10 )
Cylinder (-20 28 -5 -4 -2 0 0 0 4 122 171 5 )
Cylinder (13 9 4 -2 4 0 -1 0 4 122 171 5 )
Cylinder (79 84 3 -5 5 0 0 0 7 103 58 10 )
Cylinder (59 83 -12 -5 3 0 0 0 6 182 142 13 )
Cylinder (-22 17 2 -3 -3 0 0 0 -4 241 225 1 )
Cylinder (6 -4 -2 2 3 0 1 0 4 241 225 1 )
Cylinder (10 43 -4 -5 1 0 0 0 5 182 142 13 )

Note: this is a picture, not an imbedded QD3D frame!