The group that starts with the Nodes keyword defines the numbering and the coordinates of the nodes. For the building model example the definition is like this:
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This is the node definition group.
Node Number, X-coordinate, Y-coordinate, Z-coordinate.
Nodes
1 0 0 0
2 0 0 15
3 0 0 30
4 15 0 0
5 15 0 15
6 15 0 30
7 0 15 0
8 0 15 15
9 0 15 30
10 15 15 0
11 15 15 15
12 15 15 30
This group has three fields per record and as many records as there are nodes in the geometry. The first field of a record (column number 1) is the global node number which must be unique, the next tree fields (columns) are the (X,Y,Z) coordinates of the node. There are no restriction on which units to use for the coordinates except that X, Y and Z should be specified with the same units. In this example, the dimensions are specified in cm.
Note: A node number must be a positive non-zero integer.