# Difference between revisions of "User:Plussai/GSoC 2012 log"

## 7 May 2012

• build the brl-cad svn on VM successfully.
• build the brlcad-7.18.4 on windows(vs2005),but some link error occured from libtclcad.lib(solved go_init(..)undefined)

## 8 May 2012

• get familiar with the Brep structure.
```    ON_CurveArray m_C2;//Pointers to parameter space trimming curves (used by trims)
ON_CurveArray m_C3;//Pointers to 3d curves (used by edges)
ON_BrepEdgeArray m_E;//edges
ON_BrepFaceArray m_F;//faces
ON_BrepLoopArray m_L;//loops
ON_SurfaceArray m_S;//Pointers to parametric surfaces (used by faces)
ON_BrepTrimArray m_T;//trims
ON_BrepVertexArray m_V;//vertexs
figure:[1]
```

## 9 May 2012

• solve the link problem when build brlcad_18.4 in vs2005.(function go_init(..) undefinded)
• understand some important point about NURBS. 3D NURBS is not tensor product surface,but it can be represented into tensor product surface by mapping 3D NURBS into 4D using homogeneous coordinate.(The NURBS BOOK page 30)
• circle Arc can be represented by vector{(1,1,0,1),(1,1,1,1),(2,0,2,2)}in yz plane

## 10 May 2012

• build brlcad-SVN successfully on my ubantu.(PS:/sh/make_deb.sh is a good tool)
• study some about Nonuniform Scaling of Surfaces.

## 12 May 2012

• find that the ehy.brep is lack of face and loop in brep structure.add them to make a correct brep.
```   int surfindex = (*b)->m_S.Count();
(*b)->NewFace(surfindex - 1);
int faceindex = (*b)->m_F.Count();
(*b)->NewOuterLoop(faceindex-1);
```

## 13 May 2012

• find that computing the longest edge size is in the bspile/nurb_tess.c and the nurbs is represented by the form of struct face_g_snurb that is different from the ON_BrepSurface.It needs to implement a new interface for the longest edge size.

## 15 May 2012

• configure some plug-in unit for my vim (e.g ctags,cscope,winmanger)

## 19 May 2012

• submit a patch of brep_debug.cpp.check if the index is in the range and string of letter.

## 23 May 2012

• update the patch of brep_debug.cpp.add the sub command 'info T','info E' for display the information of trims and edges in brep.Also, make the 'info' dispaly the information in a range of indexed elements for keeping sync with the 'plot'.

## 25 May 2012

• add a subcommand 'plot SCV' to display nurbs control point net

## 27 May 2012

• waste a lot of time to test the opennurbs' API of:
``` int CreateMesh(const ON_MeshParameters& mp, ON_SimpleArray<ON_Mesh*>& mesh_list) const;
```
• but,it seems difficult to make a good ON_MeshParameters to create mesh successfully.read the sources of opennurbs_mesh.cpp
```ON_Mesh* ON_BrepFace::CreateMesh(
const ON_MeshParameters& mp,
ON_Mesh* mesh
) const
{
return 0;
}
```

## 29 May 2012

• do some works on converting nurbs curve and surface to bezier

## 31 May 2012

• do some works on comput the intersection between a line and a bezier curve/surface
• some materials: the nurbs book and Curves and Surfaces for Computer Aided Geometric Design: A Practical Guide.

## 1 June 2012

• implement RT_ADD_VLIST(vhead, pt1, BN_VLIST_POINT_DRAW) in src/libdm/dm-plot.c but it seems that dm-plot.c has nothing relation with the brep_debug.cpp

## 2 June 2012

• implement RT_ADD_VLIST(vhead, pt1, BN_VLIST_POINT_DRAW) in src/libdm/dm-ogl.c and upload the patch.
• make progress for subcommand 'plot SCV' in mged.The patch can display not only the control net,but the control point.

## 4 June 2012

• one step that make 2d trimming curve into 3d can be skip because the BREP struct has the edge in 3d corresponding to the 3d trimming curve.
• study the qd tree and kd tree for subdivision of nurbs surface in paper and the approximation error for the subdivision.

## 6 June 2012

• figure out the coving triangles to avoid cracks when making boundary curve tessellation.
• figure out the trimming curve tracing when splitting the trimming curve into bezier patch.(the active edge,active leaftree)

## 8 June 2012

• read the opennurbs API and find the ON_NurbsCurve::MakePiecewiseBezier() can clamps ends and adds knots so the NURBS curve has bezier spans (all distinct knots have multiplitity = degree) ,the ON_NurbsSurface also has the same member method.It is a better way to convert trimming curve and surface into bezier
• read the opennurbs API and find the ON_NurbsCurve::InsertKnot() can make the conversion between Nurbs and Bezier if setting the parameter multiplicity equal to degree.,the ON_NurbsSurface also has the same member method.

## 10 June 2012

• add 'info TB' 'SB' to display information piecewise bezier of trimcurve and surface.patch has been upload
• add 'plot TESS index plotres' to draw the trimesh of a nurbs surface. the tess has not taken apporimmation into consideration and just simply subdivide u,v into plotres steps;

## 12 June 2012

• upload the patch to implement the adaptive bezier subdivision and triangle mesh display which includes the function bezierApporixmation(...),bezierSubdivision_kdtree..
• read opennurbs_ext.cpp,especially figuring out the function of
``` BBNode* SurfaceTree::surfaceBBox(...)
BBNode* initialBBox(...)
BBNode*SurfaceTree::subdivideSurfaceByKnots(...)
BBNode* SurfaceTree::subdivideSurface(...)
```
• SurfaceTree::subdivideSurfaceByKnots and BBNode* SurfaceTree::subdivideSurface can help me to create the kd/qdtree as a represent of bezier subdivision.But the recursion termination condition is different.

## 14 June 2014

• In function of SurfaceTree::subdivideSurface() at src/opennurbs_exp.cpp,line 1528 to 1531:
```           const ON_Surface* surf = m_face->SurfaceOf();
localsurf->FrameAt(u.Mid() - uq, v.Mid() - vq, frames[5]);
localsurf->FrameAt(u.Mid() - uq, v.Mid() + vq, frames[6]);
localsurf->FrameAt(u.Mid() + uq, v.Mid() - vq, frames[7]);
localsurf->FrameAt(u.Mid() + uq, v.Mid() + vq, frames[8]);
```

Interval u,v is in gloable area, So I think the four lines above need to be modified.

• Read the BBNode structure in opennurbs_exp.cpp, BBNode will be used to represent the node in qd/kd tree and handling the trimcurve.

## 16 June 2012

• upload a patch in opennurbs_ext.cpp
• add three functions below to subdivide bezier,in opennurbs_ext.cpp
```           BBNode* subdivideSurfaceToBezier(...)
BBNode* subdivideBezier(...)
double getBezierApporixmation(...)
```
• add two functions below to create BezierTree root as the struct of BBNode
```          bool setFace(ON_BrepFace* face, bool removeTrimmed);
BBNode* createBezierTreeNode();
```

## 18 June 2014

• compare surface split between
```           BBNode* subdivideSurfaceToBezier(...)
BBNode* subdivideBezier(...)
and
BBNode*SurfaceTree::subdivideSurfaceByKnots(...)
BBNode* SurfaceTree::subdivideSurface(...)
```

the original method seem to be unsymmetric when split ell.brep sphere.brep. But the new method has not taken the edge length into consideration,so the ratio of lengths in u,v direction may be too long or too small.

• understand SurfaceTree::subdivideSurface() at src/opennurbs_exp.cpp,line 1528 to 1531, it comes to the same result when replacing localsurf into surf because the localsurf's domain is change along with the split.

## 20 June 2012

• figure out the functions below in brep_debug.cpp which is used to draw trimmed BBNode of surface.But these functions seem not be able to remark the intersections of BRNode and trimcurve
```           void drawBBNode(....)
void drawisoU(....)
void drawisoV(....)
void drawisoUCheckForTrim(.....)
void drawisoVCheckForTrim(.....)
```
• figure out the trimflag of BBNode: m_trimmed,m_checkTrim and the function of preptrim() in opennurbs_ext.pp.

when a BBNode is remark as m_trimmed is true, the BBNode has been remove out from the surface. When a BBNode is remark as m_trimmed is true, the BBNode in uv region has intersections with the BRNode of trimcurve,so it need to be check again and compute the interections if needed.

## 22 June 2012

• figure out the functions below in opennurbs_ext.h which can help me to comput the intersection between BBNode and trimcurve.
```      fastf_t BANode<BA>::getCurveEstimateOfU(fastf_t v, fastf_t tol) const
fastf_t BANode<BA>::getCurveEstimateOfV(fastf_t v, fastf_t tol) const
```
• add a function below to return the parameter t of the intersection based on the two functions above
```      template<class BA>
fastf_t BANode<BA>::getCurveEstimateOfT(fastf_t value, bool direction, fastf_t& t, fastf_t tol) const
```
• add a function to sort the BRNode in CurveTree by the t in parameter region.
```     sortT(BRNode* first, BRNode* second);
```

## 24 June 2012

• implement TrimNode and TrimLoop to represent the struct of untrimmed regions in parameter area.some functions included below:
```      TrimLoop(ON_Interval m_u,ON_Interval m_v):tol(0.000001);//construct
TrimNode* findPos(TrimNode* n);//find the position to insert for a new trimnode
TrimNode* findSamePoint(const ON_2dPoint& pt);//find the node whose point in parameter is equal to pt
bool linkOnTrimNode(TrimNode* pre,TrimNode* next);//link two trimnode which both within the bboxing
bool insertInEdge(TrimNode* pos, TrimNode* n);//insert a new node
TrimNode* travelLoop(TrimNode* n,int step);//travel from a trimnode to form a close loop
```

## 26 June 2012

• start to implement BVNode<BV>::doTrimming function in opennurbs_ext.cpp.
• implement getLeavesIntersection(....) to find the bboxings of curveleaves which have intersections with the BBNode in UV region
• calculate the intersection between edge of bboxing and trimcurve's leaves(bottom,top,left,right)
• solve some special sitiuations: intersection on the conner of bboxing.