As the subject line says, my head mesh currently mapped and unwrapped developed an onset of small sections breaki g down into tris. Not the whole map just sections.
What happened was i have two head meshes, same character with slightly different expressions. I needed to fix some changes in the newer one (the eyes) wanting to revert to original appearance. I therefore borrowed from the earlier head - the region of the eyes and connecting nose bridge. importing the piece to correct the damage. (Saved as wavefront)
I Joined the new OBJ rgion to the head mesh and then stitched it together in edit mode. Then I selected all verts and removed doubles and assigned the entire mesh to the texture map. Alleo after recal ulati g outside. No drama so far. Until I went to the UV map.
Two things - the new piece imported fine but the edges I had to extrude to join the old and new. However this newly extruded strip did not appear in the uv map. So there was now a figure eight racetrack gap running around the etes and across the nose bridge . So … I highlighted the newly extruded faces and Then unwrapped them seprately onto the existing map and then welded the new and old verts.
Not bad except for certain areas, which kept sudividing into tris. Which was immensely irritating to an already long and tedious repair. Also the “live UV update button checked”