Why MergeEdge does not work on selected edges?

Why MergeEdge choose strange random edge pairs which it can merge and it does not merge edges which I want it to merge? This works strangely in my opinion and it`s not intuitive.

I would like to select some continuous part of the surface edge (pick a few chosen edges and merge them). I waste a lot of time on things like this. You receive instead two propositions which are mostly not what you want or you can merge all which is also not what you want. So you need to DupBorder, UntrimAll, Unjoin and merge all needed curves manually. After that is needed often to extend more complicated surface edges and trim out the outer surface, It`s a huge waste of time IMO.

This is a perfect circle so it’s continuous in its nature and should be merged in any way like a breeze but it`s not. You need to make many hits to merge what you want. This is a simple circle shape and if I have more complicated surfaces then I do it much longer.

Please do something with that. This is version 7.


perfect_circle_mergeedge_test.3dm (47.8 KB)

Hello- I am not sure I follow - Are you saying you would like to simply select all the edges to merge ‘by hand’ and then let Rhino merge these as much as possible? That seems to me like a plausible workflow - with a ChainEdges option- am I understanding your point?


Thanks for the fast reply.
Please try to Merge those three edges fast and you will see what I mean.


or even try to merge those two edges fast:


Hello- it works fast here to select edge A or B or Both from the menu, but what would not work fast would be to select two non-continuous sets of edges and just merge them, which was how I read your comment - it takes two runs of the command.
Merging these two sets of edges is not possible in one run of the command.

I’d also prefer an edge display to show up during the command showing the edge end points…


but on my comp options, ‘A’.‘B’. and ‘All’ are not what I want in 90% of cases.
I want to have the possibility to merge what I want to merge if it`s neighboured and continuous.

Is it possible to report it somewhere to add that feature?

Sorry, I am not sure I fully undertstand yet - in the examples you give, A,B ,or Both works - What I think you may want is a Next/Previous menu item to add edges one at a time to get all the ones you want ?


My Idea was that if you have a selection of neighboured and continuous edges of the same surface while triggering the MergeEdges command then they should be simply merged.

What is the reason for randomly choosing two options A and B?

second way would be possibility of using Ctrl+LMB to pick selected edges after triggering command to choose what you want (if they are neighboured and continuous). This option should allow multiple continuous edges in one chain.

If you select an edge, there are at most two edges that can be merged with it directly - one on one side, one on the other, A and B. These are highligthed as you mouse over the menu item. Or both.
However, I do get that there may be more useful ways to merge edges - it is a good one to think about…
RH-80332 MergeEdge workflow

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Thanks. Showing points on edges during working MergeEdge command is also a great idea (as you said above) because when I was a fresh user I didn’t know what was going on. After some operations (OffsetSrf for example you will get surfaces with many point’s on the edges and it`s easy to get lost there during cleaning up.

I would forget about using MergeEdge. It doesn’t really do anything other than fool you into believing that it does do something.

If you duplicate the border before trying to merge the edges and explode that border curve you get 7 segments. If you duplicate the border after you are done merging all the edges and explode it it will give the same 7 segments. Nothing really has been done to the edges to fix them by MergeEdge. They may still cause the same problems that fragmented edges cause.

If you really want those edges fixed, then untrim the surface using the option KeepTrimObjects=Yes. Then run SimplifyCrv on the result and then trim the surface again.

After doing the above you can run DupBorder and Explode and you will get the commandline message:
“Cannot explode single curve segments”

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I used that merge edge command mostly for some other commands which need to have merged or split edges correctly. For example Xnurbs (it needs split edge), EdgeSrf (tri or quad edges input), Sweep2 (sweep shapes need to have a single edge).