Moving solid points of polysurfaces creates bad surfaces

I see this many times and I don’t understand the reason.

I use Solidpton and then move.

Hi Bogdan,
I’m not seeing that in a similar shape here. Could you post a file with clear instructions?

I can’t replicate this now. It happens quite often, I’ll save a file next time I bump into it.

Wim, this happens a lot. I have not seen it in all degree-1 surfaces, but if you have any degree-2 extrusion-like all hell breaks loose. If you grab a bunch of objects and models and start doing any solid editing by selecting a face and move it, or by selecting solid points, you’ll see the issues clearly.

We stopped using direct editing unless is an extremely simple, prismatic form with all flat faces, and we cad easy check for damage. These tools are a total liability for us.


I think these commands are handy for simple, flat, degree=1 surfaces. For fun, I model and build Arts and Crafts style furniture. You can’t get much more simple and prismatic than that. You certainly can screw things up with them.
Like many commands in Rhino they can be dangerous in the hands of someone that doesn’t understand what they do.
I put it in the same class as JoinEdge and MeshToNURBS.

I think if you work a little harder at keeping your surfaces as perfectly simple as you can, you’ll generally have better luck with these tools. Keep your coplanar, degree 1 surfaces merged and with as few points as possible and you should be unpleasantly surprised less often.

Hi all,

I bumped into another one. And on simple geometry, please check file. Moving the vertical edge that I marked with a line will destroy 2 surfaces of the polysurface. Same thing if i use solidpton or i just grab the edge with ctrl+shift+click and move it.

EDGE MOVE BUG.3dm (76.9 KB)

The distortion also occurs if you move the bottom edge pointed to by the line.

The UV direction of the face these edges bound is skewed. If you extract and delete the face and then cap to replace it, the edge moves work without distorting the other face.

So there does appear to be a bug, related to UV directions.

Problems are likely to be due to too far from the origin.
Added: Moving the object close to the origin prevents the problems from occurring when moving solid points.

World coordinates:
min = 91958835.147,437728033.891,12013.300
max = 92042569.576,437773256.634,19213.300
dimensions = 83734.429, 45222.743, 7200.000 millimeters

Hi @Bogdan_Chipara,

As @davidcockey points out, your object is very far from the origin and large. This element alone is over 80m long, but you are modelling it using a mm scale and to an accuracy of 0.001mm. You would be better served by starting from the “large objects - metres” template and modelling in metres.

Secondly, the “vertical” edges of the face pointed to by the line are actually slightly off vertical. I don’t know if the edges are off vertical by design, but this means that you are going to lose the planarity of each adjacent face when you move the edge (except where the movement direction is in the plane of that face). If you do a lot of moves like this you will gradually increase the complexity of your model faces and make it more likely that problems occur. This may well be a factor in the original problem you posted.


I played with the volumemore.
So I’ve made a new extrusion starting from the lower surface.
I blended the verticals, started to move the edges… it works fine, in the same file, same conditions small tolerance, far away from origin…