Polygons > Edit Polygons reconstructs individual triangles.
Use the Primitives Manager to verify that Edges are turned on, zoom in to see a group of polygons in detail, start this function, click one of four radio buttons, and click a point on an existing edge in the Viewing Area. Use Ctrl-Z to undo the most recent edit.
The effect of this function depends on which of four radio buttons is pressed:
Split Edge - the nearest point on the nearest edge is moved to the point you click, that nearest edge is split into two edges, and all edges are re-drawn.
Flip Edge - the endpoints of a selected edge are moved to the other two corners of the quadrangle that is formed by the two triangles that share that edge.
Contract Edge - all six edges of the two adjacent triangles are deleted, and a new edge is created between the selected point and each of the surrounding corners.
Add Triangle - inserts a new triangle between the three vertices you click on a natural boundary.
See also Polygons > Refine.