Editing User:NyahCheck/Survey of CSG Algorithms

From BRL-CAD

User account "NyahCheck" is not registered. Please check if you want to create/edit this page.

Warning: You are not logged in. Your IP address will be publicly visible if you make any edits. If you log in or create an account, your edits will be attributed to your username, along with other benefits.

The edit can be undone. Please check the comparison below to verify that this is what you want to do, and then save the changes below to finish undoing the edit.
Latest revision Your text
Line 5: Line 5:
 
= Personal Information =
 
= Personal Information =
  
Name: Nyah Watad Check.
+
Name: Nyah Watad Check
Email: check.nyah@gmail.com.
+
Email: check.nyah@gmail.com
IRC Nick: Ch3ck, Ch3ck_.
+
IRC Nick: Ch3ck, Ch3ck_
  
 
== Background Information ==
 
== Background Information ==
Line 19: Line 19:
  
 
* Google Summer of Code Participant, BRL-CAD, April - September 2013
 
* Google Summer of Code Participant, BRL-CAD, April - September 2013
**Implemented a pull routine to reverse the effects of a push on Geometry.
+
**Implemented a pull routine to reverse the effects of a push on Geometry, **integrating command into MGED interface. (C, XML, 500+ lines of code)
**Integrated command into MGED interface. (C, XML, 500+ lines of code)
 
 
**Tested the polynomial and matrix math routines, improving the speeds of the inverse matrix and matrix determinant routines by over 10%. (C, 300+ lines of code)
 
**Tested the polynomial and matrix math routines, improving the speeds of the inverse matrix and matrix determinant routines by over 10%. (C, 300+ lines of code)
 
**Integrated the xpush routine which pushes objects having more than a single matrix transformation into the push which pushes object matrix transformations to leaf nodes. ( C, 1000 lines of code.)
 
**Integrated the xpush routine which pushes objects having more than a single matrix transformation into the push which pushes object matrix transformations to leaf nodes. ( C, 1000 lines of code.)
Line 30: Line 29:
 
**Languages: C(Excellent), Java( Excellent ), C++( Beginner), Bash(Excellent), SQL(Proficient)
 
**Languages: C(Excellent), Java( Excellent ), C++( Beginner), Bash(Excellent), SQL(Proficient)
 
**Tools: Secure Shell, subversion, Git, Linux, Netbeans, gdb, valgrind.
 
**Tools: Secure Shell, subversion, Git, Linux, Netbeans, gdb, valgrind.
 +
 +
  
 
= Synopsis/ Proejct Summary =
 
= Synopsis/ Proejct Summary =
Line 39: Line 40:
  
 
Constructive Solid Geometry is a technique used in Solid modeling which allows a modeler to create a complex surface using Boolean operators to combine objects. This is often referred to as procedural modeling and can be performed on polygonal meshes. Here, the simplest solid objects used for representation are called primitives which are used to construct more complex objects using allowable Boolean operators such as union, intersection, difference and well as geometric transformations on those sets of objects.
 
Constructive Solid Geometry is a technique used in Solid modeling which allows a modeler to create a complex surface using Boolean operators to combine objects. This is often referred to as procedural modeling and can be performed on polygonal meshes. Here, the simplest solid objects used for representation are called primitives which are used to construct more complex objects using allowable Boolean operators such as union, intersection, difference and well as geometric transformations on those sets of objects.
 
 
OpenSCAD uses the Clipper Library to implement CSG in 2D and CGAL libraries to model 3D surfaces. My objective in this study is to look at the CSG Algorithms implemented by OpenSCAD and do a comparative study with other CSG algorithms, performing and algorithmic analysis and implement prototypes which can be useful in the OpenSCAD framework.
 
OpenSCAD uses the Clipper Library to implement CSG in 2D and CGAL libraries to model 3D surfaces. My objective in this study is to look at the CSG Algorithms implemented by OpenSCAD and do a comparative study with other CSG algorithms, performing and algorithmic analysis and implement prototypes which can be useful in the OpenSCAD framework.
 
This entails studying 4 main research papers together with various implementations of the algorithms associated with them and implementing the most efficient on the OpenSCAD platform.
 
This entails studying 4 main research papers together with various implementations of the algorithms associated with them and implementing the most efficient on the OpenSCAD platform.
  
 +
= Links =
  
==CSG Algorithm for OpenSCAD(Current Implementation)==
+
= Deliverables =
 
 
OpenSCAD is a parametric CSG based modelling software; which means objects are manipulated by editing the CSG descriptions of objects being rendered. It employs two different mechanisms for processing CSG descriptions. It uses the OpenCSG library for visualization during editing and the CGAL library for export created a meshed BREP output. However, the OpenCSG Library uses the Goldfeather and  SCS  algorithms to evaluate the 2D images of a CSG object from the given perspective. This is beneficial  because of  its speed and ability to render complex images within a short time.
 
 
 
However, CGAL employs the Nef Polyhedra for evaluating boolean operations  on CSGs. It  is robust and is able to handle non manifold input but proves incredibly slow in practice and not very suitable for time critical  applications . There are also overflow  issues that arise with using large size polyhedra. The used of  BSP tree proves more efficient for CSG evaluations than CGAL's  Nef based polyhedra .
 
Below describes  the use of BSP based algorithm for CSG evaluations than CGAL's Nef-based Polyhedra  system.
 
 
 
==BSP Tree based Implementation of Boolean Operations==
 
 
 
Bernstein et all[1] presented an exact and more efficient method for evaluating 3D polyhedra  already supported by OpenSCAD. Results from tests showed for a BSP tree implementation which 16-28X faster at performing iterative computations than CGAL's Nef polyhedra . The use of a BSP-tree based boolean algorithm allows the explicit handling of all geometric degeneracies without treating a large number of cases. There are also efficient  CSG to BSP algorithms which  could be used for easy representations in both formats.
 
 
 
BSP trees afford an alternative to B-rep algorithms that avoid their concomitant case explosion by explicitly handling all degenerate configurations of geometry. They have demonstrated to have suitable performance for interactive volumetric sculpting.
 
 
 
*Numeric Substrates
 
In this system, a plane is a quadruple of floating point numbers interpreted as coefficients of a plane equation.
 
**Concidence: Two planes p, q are coincident if and only if the determinant of all 2x2 minors are 0
 
**coincident orientation:  if p and q are coincident and Pa.Qa, Pb.Qb, Pc.Qc, Pd.Qd are non negative.
 
 
 
**Point Validity: if a point A(p,q,r) is valid if i'ts determinant is non zero
 
  Pa Pb Pc
 
  Qa Qb Qc
 
  Ra  Rb Rc
 
 
 
**Orientation: Given a point A(p, q, r) is valid and it lies behind, on, or in-front of the plane S if  and only iff the following expression is negative, zero or positive
 
                            Pa Pb Pc  Pd
 
Pa Pb Pc                    Qa Qb Qc Qd
 
Qa Qb Qc      *            Ra Rb Rc Rd
 
Ra Rb Rc                    Sa Sb Sc  Sd
 
 
 
These predicates are implemented as static filtered floating-point predicates in the style of shewchuk, but deviations will be done to support double precision.
 
 
 
*Geometric Substrates
 
In the preceding step, we defined planes as primitives, points as triples of planes and 4 predicates operating on these plans; now we define a convex polygon type for a constructor and splitting routine.
 
 
 
**Convex polygon: This is a plane of support, s with a bounding plane {Bi} I £ Z. This vertices given by  Vi = (s, Bi-1, Bi).
 
 
 
**Construction of a Convex Polygon from a Plane: Given a plane h, this operation constructs a convex polygon representing h clipped by a very large box. The output polygon serves as a stand in for the infinite extent plane. A consistent axis aligned “very large box” is used for all calls to the constructor and consists of volume spaced bounded by planes X+, X-, Y+, y- , Z+, Z-.
 
 
 
**Splitting a Convex Polygon by a Plane: Since  polygon splitting may be viewed as two successive and complementarty instances of polygon clipping. The algorithm below similar to the Sutherland-Hodgman style polygon clippers, rather than deciding if and when to insert a crossing point to the output stream, we decide if and when to insert the splitting plane into the output stream.
 
 
 
==Algorithm ==
 
If s is concident with h
 
  if s is similarly oriented to h
 
      Return (s, {Bi}i e Zn)
 
  Else
 
    Return nothing
 
Else
 
  For I e Zn(in order)
 
      Output planes as specified by table lookup using:
 
      o(s, bi-2, bi-1, h)
 
      o(s, bi-1, bi, h);
 
      o(s, bi, bi+1, h)
 
    Return (s, output)
 
                  Algorithm: Clip(s, {bi}i e Zn) by h
 
 
 
The Above algorithm works in interoperability between input and output that is between the Point-based polygon soup and the Plane-based Representation working with Boolean operations.
 
 
 
= Sample Algorithms/Links =
 
 
 
* Gilbert Bernstein and Don Fussell: Fast, Exact, Linear Booleans
 
*Sebastian Steuer: Methods for Polygonalization of a Constructive Solid Geometry Description in Web-based Rendering Environments
 
 
 
* MEPP: Exact and Efficient Booleans for Polyhedra
 
*Cork - by Gilbert Bernstein
 
* CGAL: http://www.cgal.org/
 
*http://liris.cnrs.fr/mepp/
 
 
 
=Testing and Verification=
 
 
 
Test would be written to verify and test the robustness of the BSP-tree based algorithm for CSG evaluations. This could apply Octoball tests from single operations between sizable meshes to Random Boxes tests and Sculpt Bunny depending on the efficiency. Also, the heat sink test which has proven to have a worst case performance of O(n2) in the size of input can be applied to the aforementioned implementation. Unit tests will be developed to handle different aspects of the BSP-tree evaluations and appropriate documentation attached for later works on the system.
 
Also, any bugs coming up during this process will be fixed and documentation of this work done during development since OpenSCAD is actively developed and this will keep other developers informed on any changes taking place in the CSG module for OpenSCAD.
 
 
 
=Deliverables=
 
*A paper containing the CSG Algorithm survey and it's relation to OpenSCAD
 
*Prototype implementations integrated with OpenSCAD on the more efficient and robust CSG Algorithms.
 
*An Evaluation of how more advanced modeling techniques could be realised with each algorithm.
 
  
 
= Development Schedule/Timeline =
 
= Development Schedule/Timeline =
This is a tentative plan which will be modified and developed as GSoC proceeds.
 
 
*May 17 – June 06( 3 weeks)
 
**Study papers on this topic
 
**Discuss with developers on implementation specifics and further clarifications on CSG Algorithms supported by OpenSCAD.
 
 
*May 24 – June 13 ( 3 weeks)
 
**Check current implementation of the BSP tree algorithm for evaluating CSGs and porting to OpenSCAD.
 
**Implement the BSP-tree representations  in OpenSCAD or optimize current implementation.
 
**Testing, debugging and documentation.
 
 
*June 14  – June 20( 1 week)
 
**Unit tests for BSP-tree routines
 
**Testing degenerate cases.
 
 
*June 21 – July 4 ( 2 Weeks) Mid Term Evaluations
 
**Add functionality for CSG to BSP-tree conversion
 
**Testing for robustness and degenerate cases.
 
 
*July 5 – July 11( 1 week)
 
**Implement testing suite for BSP tree implementation of the Bernstein algorithm.
 
**Adding documentation to OpenSCAD framework
 
 
*July 12 – July 25 ( 2 weeks)
 
 
**Implement and test subroutines for Numeric substrates.
 
**Testing and debugging.
 
 
**July 26 – August 8 ( 2 Weeks)
 
**Add functionality for Geometric Substrates together with sub routines.
 
**Testing and debugging of Convex polygon constructor for clipped plane
 
 
*August 9 – August 22( 2 Weeks)
 
**Inside-out tests, address robustness issues with modules and improve performance of libraries.
 
**Write paper on Comparison of CSG based algorithms in relation to OpenSCAD Implementations.
 
**Check code for memory leaks and performance analysis, with unit tests added for implemented modules.
 
 
*August 23 – August 29( 2 weeks)
 
**Pencils Down, Code clean up.
 
**Review documentation and Finalize paper writing.
 
**Final evaluation, Submission of code to melange.
 
  
 
= Time availability =
 
= Time availability =
I would be able to offer over 40 hours on the project. However, since the project would start during our second Semester; I would be coding mostly during the nights up to late June or early July when our semester ends. Also, to meet up with the demands of the project, I would be coding during weekends  and regularly informing my mentors on the status of the project and regularly updating my logs in this respect.
 
  
 
= Why BRL-CAD =
 
= Why BRL-CAD =
After participating in GsoC 2013 with BRL-CAD, I fell in love with CAD and will love to spend my summer contributing code to improve BRL-CAD software.
 
  
 
= Why Me =
 
= Why Me =
First of all hailing from Africa with lack of computing infrastructure posed a lot of great challenges to  ascend to hackerdom especially with the scarcity of good programmers and lack of Internet access. Working with BRL-CAD in 2013 taught me a great deal especially working with the brightest researchers in this field. I believe my participation in GSoC this year would not only give me a great learning experience but also heighten my ambition of being a great Computer Science researcher in Africa. I see this  project as both an intellectual challenge to impact change through open source software.
 
 
= Contributions =
 
 
 
== Past Coding Work ==
 
 
*GSoC 2013:
 
**http://www.google-melange.com/gsoc/project/code_samples/google/gsoc2013/ch3ck/5721450489053184
 
 
*Xorg Evoc 2014
 
**https://github.com/Ch3ck/xorg-xserverhttps://github.com/Ch3ck/xorg-xserver
 
 
*Other Projects
 
**https://github.com/Ch3ck/SAMS
 
**https://github.com/openmrs/openmrs-core
 
 
 
==Current OpenSCAD work ==
 
 
Here are my current and ongoing contributions on OpenSCAD
 
* Rework AbstractFunction::evaluate to virtual function only fixing calls
 
**https://github.com/openscad/openscad/pull/1285
 

Please note that all contributions to BRL-CAD may be edited, altered, or removed by other contributors. If you do not want your writing to be edited mercilessly, then do not submit it here.
You are also promising us that you wrote this yourself, or copied it from a public domain or similar free resource (see BRL-CAD:Copyrights for details). Do not submit copyrighted work without permission!

To edit this page, please answer the question that appears below (more info):

Cancel Editing help (opens in new window)