Given that the vertices half way are on all the same hight:
* I would draw a quad (looking from above) so that is 90 degree to the current triangles
* Set y of the quad to the hight of the vertices
* Select the quad and the triangles
* Isecalc
* You'll get vertices at the correct intersections
* Use those vertices to redraw the triangels
* I would draw a quad (looking from above) so that is 90 degree to the current triangles
* Set y of the quad to the hight of the vertices
* Select the quad and the triangles
* Isecalc
* You'll get vertices at the correct intersections
* Use those vertices to redraw the triangels
LEGO ergo sum