Hi!
I have been using rhino 6 for a long time but I didn’t see any fourth point before when I make a triangular surface. After making surface I use the command PointsOn and fourth corner appears like in the picture.
Are there any settings for that?
Edit: I put the example file with the sample objects that have the problem I am talking about.
example.3dm (2.6 MB)
Hi, you must be using this 
command “Surface from 3 or 4 corner points”.An alternative is to use the UnTrim command and then move one of the control points over another to merge them, that way you will get what you are looking for. “if you don’t undo the clipping it doesn’t work”
Another identical way, the difference is to omit the SrfPt command and use plane then activate your control points and move it directly over the other point. view image
Thank you for the recommendation but I also have the similar problem when I extrude a line and make a surface
Just two dots and another dot linked to them appear when I use the command Points On.
I tried updating rhino but it didn’t work.
Do you have the same situation when you use SrfPt command?
I feel like there is something wrong going on 
just use explode command
You can also configure it from the command UseExtrusions to make surfaces instead of extrusions
Thanks again for the reply that worked but I had one more problem like this while modeling.
I created a surface then trimmed it and it had surface points on way too far. Then I used the command ShrinkTrimmedSrf it took points closer but still not on the surface.
Im so new to this situation. Still couldn’t figure out why are these happening.
Yes, it is correct both ShrinkTrimmedSrf and Shrink Trimmed SrfT Edge shrink sitrimmed surfaces and rebuild the control point structure. otherwise you must upload an example for someone on the forum to review.
Alright. I put the example file to the first entry.
Hello - ShrinkTrimmedSrf leaves a small - ~1%, if I remember correctly, outside the trim curve when the trim curve does not correspond to a surface isocurve. This is because trims that are not on isocurves are approximate - subject to the document absolute tolerance. The ides is to avoid having the trim curve fall outside the surface by some near tolerance amount - that is bad and should be avoided. ShrinkTrimmedSrfToEdge will attempt to shrink completely, but on non-isocurves trims runs the risk described…
-Pascal
thanks pascal
all these problems started happening 2 days ago. I didn’t have all three problems I mentioned in here before. I’m not used to work like this. I do everything suggested here while modeling but it makes me so slow.
Are there any ways to prevent making trimmed surfaces?
PlanarSrf will result in a trimmed surface unless the planar curve is exactly a rectangle.
Trim or Split will result in a trimmed surface unless the trimming or splitting object is exactly aligned with an isocurve in the surface to be trimmed or split.
Boolean commands will frequently result in trimmed objects unless the surfaces a exactly aligned with isocurves.
Some other commands may result in trimmed surfaces.
Trimmed surfaces can be very useful. It is best to learn how to work with trimmed surfaces.
