# Shapr3D randomly adding many control points

**URL:** <https://discourse.shapr3d.com/t/shapr3d-randomly-adding-many-control-points/13477>\
**Category:** Modeling Questions\
**Created:** [June 24, 2021, 12:01am UTC](https://discourse.shapr3d.com/t/shapr3d-randomly-adding-many-control-points/13477 "2021-06-24T00:01:03Z")\
**Posts on this page:** 1\
**Showing post:** 38

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**Author:** ![PEC](https://avatars.discourse-cdn.com/v4/letter/p/67e7ee/32.png) [@PEC](https://discourse.shapr3d.com/u/PEC)\
**Post date:** [July 23, 2022, 10:15pm UTC](https://discourse.shapr3d.com/t/shapr3d-randomly-adding-many-control-points/13477/38 "2022-07-23T22:15:58Z")

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Hi,

here is a way to reproduce the issue:

- create a clean ellipse using the ellipse tool and lock it
- extrude the ellipse with -5° **negative draft angle**
- go back to the sketch with the created body visible
- draw a line intersecting the ellipse

_The clean ellipse, which was **locked** , seems to be replaced by a mess of control points._

Actually, a new curve has been created above the original ellipse. If you select the new curve and delete, then you get the original ellipse in place **but the locked ellipse has been also modified: now, when extruding, there is an unwanted face added**.

> [@Bucket tutorial](https://discourse.shapr3d.com/t/bucket-tutorial/20498/2):
>
> Hi Barryd this is clearly a bug. @Shapr: the original sketch is modified when doing extrusion with negative draft angle, even if we lock it previously to the extrusion. (Positive draft angle does not trigger the issue). This shows that locked sketches can be modified, which obviously is not the expected behavior. I still don’t fully understand what you are doing with sketches when we extrude bodies. Looks like you are recreating the locked sketch by projecting the body to the sket…

I understand that there is an automatic edge projection on the sketch, when we draw on a face of a body; this can be useful on certain occasions, this can be painful on other situations, _but this cannot mask or modify a clean locked curve_.

Looks like the solution could be **not to project** when the projected curve is very close to an existing curve (distance less than the internal tolerance), **and no sketch modification at all when extruding a body** [Edit] probably no cache modification or invalidate the cache entry, see below.

Best  
PEC

[Edit]  
I made a few additional investigations.  
For the “locked ellipse has been also modified”, here is what I think:

- the original sketch is not actually modified: if you export it in DXF format, you get the same sketch before and after the issue occurs;
- **but Shapr3D is probably using _a cached version_ of the sketch for performance optimisation, and this version is modified by the extrusion, so for the end users, it looks like the sketch has been modified** ;
- as soon as you made a modification on the curve, it invalidates the cache entry for the curve and you revert to the correct curve definition, probably creating a new cache entry;
- if you copy the curve, the copy is correct also, probably because the copy does not use the version in cache, which is a very good thing 😀

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