Extrude Base Option Changes Boundary of an open mesh

[cometKim96]

Hi.
I'm trying to remove Undercut parts of an open mesh and I found Extrude Base in MeshInspector.

I tried findUndercuts & fixUndercuts, and it removed undercuts. But it changes boundaries of open mesh.
Is there any way I can extrude undercut parts of open mesh while keeping non-undercut part untouched?

Thanks!

[Grantim]

Hello!

Right now our algorithm is based on voxles conversion, so result mesh is completely rebuild. (this particular algorithm requires closed mesh on input, so if mesh is open we close it ourselves before applying).

We will consider implementing another algorithm or an option in this one to support open mesh.
Thanks for the question!

P.S.
Could you please explain why closing mesh don't work for you?

[cometKim96]

Thanks for your reply!

I also tried closing -> extruding mesh -> cutting. Closing mesh kept original boundary positions but after extruding those positions were kind of smoothed I guess? My business logic strictly forbids changing boundaries of open meshes.

Extruding Mesh.zip

[Grantim]

Thanks for the data!

Unfortunately now there is now simple way to preserve boundary after calling fixUndercuts because it rebuilds mesh completely.

One thing you can try is something like this:

1. Save boundary as polyline
2. fixUndercuts
3. Project saved polyline to mesh and move it a little up

   MeshLib/source/MRMesh/MRContoursCut.h

   Lines 97 to 106 in d717e06

   	/** \ingroup BooleanGroup
   	* \brief Makes continuous contour by iso-line from mesh tri points, if first and last meshTriPoint is the same, makes closed contour
   	*
   	* Finds shortest paths between neighbor \p surfaceLine and build offset contour on surface for MR::cutMesh input
   	* \param offset amount of offset form given point, note that absolute value is used and isoline in both direction returned
   	* \param searchSettings settings for search geodesic path
   	*/
   	[[nodiscard]]
   	MRMESH_API Expected<OneMeshContours> convertMeshTriPointsSurfaceOffsetToMeshContours( const Mesh& mesh, const std::vector<MeshTriPoint>& surfaceLine,
   	float offset, SearchPathSettings searchSettings = {} );

4. Cut mesh above old bounday

   MeshLib/source/MRMesh/MRContoursCut.h

   Lines 219 to 235 in d717e06

   	/** \ingroup BooleanGroup
   	* \brief Cuts mesh by given contours
   	*
   	* This function cuts mesh making new edges paths on place of input contours
   	* \param mesh Input mesh that will be cut
   	* \param contours Input contours to cut mesh with, find more \ref MR::OneMeshContours
   	* \param params Parameters describing some cut options, find more \ref MR::CutMeshParameters
   	* \return New edges that correspond to given contours, find more \ref MR::CutMeshResult
   	* \parblock
   	* \warning Input contours should have no intersections, faces where contours intersects (`bad faces`) will not be allowed for fill
   	* \endparblock
   	* \parblock
   	* \warning Input mesh will be changed in any case, if `bad faces` are in mesh, mesh will be spoiled, \n
   	* so if you cannot guarantee contours without intersections better make copy of mesh, before using this function
   	* \endparblock
   	*/
   	MRMESH_API CutMeshResult cutMesh( Mesh& mesh, const OneMeshContours& contours, const CutMeshParameters& params = {} );

5. Stitch cut place with old boundary

   MeshLib/source/MRMesh/MRMeshFillHole.h

   Lines 85 to 106 in d717e06

   	/** \brief Stitches two holes in Mesh\n
   	*
   	* Build cylindrical patch to fill space between two holes represented by one of their edges each,\n
   	* default metric: ComplexStitchMetric
   	*
   	* \image html fill/before_stitch.png "Before" width = 250cm
   	* \image html fill/stitch.png "After" width = 250cm
   	*
   	* Next picture show, how newly generated faces can be smoothed
   	* \ref MR::positionVertsSmoothly
   	* \ref MR::subdivideMesh
   	* \image html fill/stitch_smooth.png "Stitch with smooth" width = 250cm
   	*
   	* \param mesh mesh with hole
   	* \param a EdgeId which represents 1st hole (should not have valid left FaceId)
   	* \param b EdgeId which represents 2nd hole (should not have valid left FaceId)
   	* \param params parameters of holes stitching
   	*
   	* \sa \ref fillHole
   	* \sa \ref StitchHolesParams
   	*/
   	MRMESH_API void buildCylinderBetweenTwoHoles( Mesh & mesh, EdgeId a, EdgeId b, const StitchHolesParams& params = {} );

Result might look somehow like this:

Red - fixed area
Yellow - strip of original mesh
Green - stitched area

[cometKim96]

Hi I tried the way you mentioned.

I successfully cutted mesh and I tried no.5 process, but buildCylinderBetweenTwoHoles closed mesh not as I expected.

cutting&stitching.zip

Am I doing something wrong??

Thanks!

[Grantim]

Hello!
It looks like you need to use e1.sym() instead of e1

buildCylinderBetweenTwoHoles( cutMesh1, e0, e1.sym(), params );

it is needed to have consistent directions of stitched holes

[cometKim96]

It worked! Thanks!