Make Trifans

Bring up the ‘Make Trifans’ Window by selecting the menu 'Modify->Make Trifans...'. This trifans Quad-Edge cells according to various selection criteria. Apply trifans to either the Primal or Dual manifold, by clicking the 'Primal' or 'Dual' radio button.

Dual trifans are enabled in Geodesica version 0-9-0 and later



1. The Truncate Vertex tool has made a large face at the pole of a subdivision.


2. Result after Make Trifan using the ‘Non coplanar’ option. The non-coplanar cell is turned into a Trifan of planar cells. In this instance, 20 new cells are created:


2. The result with its dual.


Dual Trifans

Dual trifans enable the construction of advanced spaceframe geometries. To trifan the Dual, ensure that the Dual radio button is ON before you click 'Apply'. Be aware that when you trifan the Dual, the Primal will update to preserve duality, therefore, any previous modelling on the Primal manifold will be lost.


Before applying Dual trifans.


After applying Dual trifans.

Trifan Sector Grouping

When creating trifans, each trifan sector is grouped according to the selected option. The following shows the results of each option on the trifanned lattice of a 4v icosahedron:


A. By Parent Group


B. By Parent cell


C. By trifan count


D. By operation count

A. Group sectors by parent group. The parent of each trifan sector is set to the enclosing cell’s parent. This option maintains the original groupings.

B. Group sectors by parent cell. The parent of each trifan sector is set to the enclosing cell. Cells with the same name that reside in different groups are now grouped together. (eg cell_13 of groups 1w, 2w, 3w, 4w and 5w).

C. Group sectors by trifan count. The parent of each trifan sector within the original enclosing cell is set to a new group altogether. The group name is “Trifan_n” where n is the trifan count. This option creates a new group for each selected cell. (Not reccommened for trifanning an entire lattice)

D. Group sectors by operation count. All trifan sectors are grouped together under a new parent. The group name is “Trifan_Op_n” where n is the operation count. When trifanning an entire lattice, this creates one group for all cells.

Trifans at a truncation plane

Geodesica-0-0-3-6j fixes a bug where a Tri-fanned lattice would fail to truncate; if using an earlier version, please truncate the sphere before making Trifans. In general apply the following rule: ‘Truncate first, model after’.

Prior to Geodesica-0-0-3-6j, Primal cells that share edges with a truncation plane were ignored when making trifans. This was to ensure that dual topology remained consistent:

primal truncation

Fig 1.

dual truncation

Fig. 2

The primal sphere in Fig 1. was trifanned according to the selection criteria 'Visible cells' but note that cells sharing edges with the truncation plane (eg: a,b,c,d) are not trifanned.