# How can you align two vertices relative to a global coordinate when you want to preserve the orientation of the edges that contain them?

I want to move a vertex A along an edge A1 in such a way so that the vertex has the same Z global coordinate as another vertex B which is in another edge B1. B1 and A1 are not parallel.

I tried using the Normal coordinate system to move A along A1, but snapping to B only considers the current (Normal in this case) coordinate system so it didn't work as desired.

Then I tried snapping the 3D cursor to an endpoint of A1 and scaling A (with the 3D cursor as pivot), but snapping to B did not work as expected (I'm not sure why).

The only solution I was able to come up with was to duplicate the edge and snap A to B in the global coordinate system, then while moving on the XY plane snapping to the duplicated edge. Far from being practical.

Here is a picture of what I'm trying to achieve:

I want the selected vertex to move only along the green axis but I want to snap to the vertex in the red circle relative to the global Z.

Is there a better way to achieve this?

• My thought is to add a second mesh object that is a plane on xy at your desired Z and big enough to intersect the relevant areas, setting its display to wire only, going back to your vertexes and sliding them with face/surface snap turned on. Can't test it right now though. Commented Dec 3, 2014 at 12:53
• @StarWeaver yes, that's better than duplicating the edge, but I didn't want to create new geometry.
– 4nt
Commented Dec 3, 2014 at 17:49

I would also like to know the answer :)

However, as a workaround for this specific case the knife tool K in combination with angle constrain C is very handy:

• The knife angle constraint snaps to the viewport so ensure you are in front or side orthographic view to get the same z value as the other vertex. Commented Dec 3, 2014 at 14:43
• This seems like the best solution so far, the only problem I see (apart from switching the 3D view) is when there are a lot of edges you don't want to cut in between the relevant edges. Dissolving a lot of vertices could become a quite slow task.
– 4nt
Commented Dec 3, 2014 at 18:09

This is a task that blender doesn't offer any help (yet).

Vertex slide GG will allow you to slide the vertex along the existing edge that you want to follow. Unfortunately snapping doesn't work during vertex slide so you need to move the vertex until you get the z value of the matching vertex. You can see the vertex position in the properties sidebar while in edit mode.

You will find it hard to get an exact value, if you get it close and then use orthographic view to zoom right in you can get small movements to get very close to the value you are after.

It is the angle of the edge that causes issues, if the edge was vertical you can move constrained to one axis and use snapping to align it to another vertex.