# Editing Libpg : A parametrics/constraint library

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+ | = libpg : A parametrics/ constraint library = | ||

Proposed sytem for parametrics and constraint implementation | Proposed sytem for parametrics and constraint implementation | ||

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acts as a library which sits above librt using the librt methods for creation and modification of geometry | acts as a library which sits above librt using the librt methods for creation and modification of geometry | ||

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− | == | + | ==Architecture== |

A constraint system can be looked upon as a system of variables, their associated domains and set of constraints/relationships between the variables. | A constraint system can be looked upon as a system of variables, their associated domains and set of constraints/relationships between the variables. | ||

− | Fundamentally this can be visualised using a constraint network which is a 3-tuple. Further we can have a graph based visualization of the same using vertices as variables and edges connecting vertices as constraints. It would be intuitive only for networks having binary (between two variables) or unary ( | + | Fundamentally this can be visualised using a constraint network which is a 3-tuple.For a mathematical review please see ( Constraint Networks by Dawn Thomas ). Further we can have a graph based visualization of the same using vertices as variables and edges connecting vertices as constraints. It would be intuitive only for networks having binary (between two variables) or unary (constraints on self) constraints. Otherwise, one has to visualize hypergraphs which contain hyperedges which is basically a line connecting multiple vertices for example. |

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− | + | Implementation of the above constraint network in the BRL-CAD system, involves 3 fundamental aspects. | |

− | + | # Domain extraction | |

+ | # Solution | ||

+ | # Geometry updation | ||

− | + | Prerequisites for such a state is of course | |

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− | # | + | # "Handle" generation and storage |

− | + | # Updated geometry storage | |

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− | + | A typical constraint solution operation is shown below. | |

− | + | ==Object Architecture== | |

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An object oriented method of implementation would be the creation of a mixed ( in the sense that they contain both geometric and non-geometric information ) object. The object architecture is as shown below which shows the data types as well as the public and private methods. | An object oriented method of implementation would be the creation of a mixed ( in the sense that they contain both geometric and non-geometric information ) object. The object architecture is as shown below which shows the data types as well as the public and private methods. | ||

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'''What should be the convention for naming the parameters ? Also there is a certain issue in the sense that some of the geometry are special cases of more generic geometry. So for a sphere we are concerned with only radius and center where as it is defined using ( point center) and 3 vectors (a b c). Should we name the parameter radius make 3 fastf_t * to a[0], b[1], and c[2] Or should we make 3 vectp_t to a,b,c or make 1 fast_t* to a[0], doing a further check/constraint that a[0]=b[1]=c[2] ?''' | '''What should be the convention for naming the parameters ? Also there is a certain issue in the sense that some of the geometry are special cases of more generic geometry. So for a sphere we are concerned with only radius and center where as it is defined using ( point center) and 3 vectors (a b c). Should we name the parameter radius make 3 fastf_t * to a[0], b[1], and c[2] Or should we make 3 vectp_t to a,b,c or make 1 fast_t* to a[0], doing a further check/constraint that a[0]=b[1]=c[2] ?''' | ||

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The datastructures necessary for the exchange of information (pc_pc_set which itself is built using a constraint set structure and parameter set structure) are defined currently in raytrace.h (Shift to pc.h in future? ) | The datastructures necessary for the exchange of information (pc_pc_set which itself is built using a constraint set structure and parameter set structure) are defined currently in raytrace.h (Shift to pc.h in future? ) | ||

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( param1= value, param2=value and so on) | ( param1= value, param2=value and so on) | ||

In this case the value is basically a region of the domain the parameter could occupy. | In this case the value is basically a region of the domain the parameter could occupy. | ||

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Initial draft/intent | Initial draft/intent | ||

− | + | It would be ideal to provide both analytical and numeric evaluation methods the second one being of primary importance in terms of constraint based calculations. | |

− | + | Considering the standard methods of parametrization ( see Enumeration below ) I think the implementation of an analytic solving system would be easier. Though for the solution of more complex equation as well as majority of constraints , libpg will have to provide support for numerical solutions. | |

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− | + | ==Enumeration of Parameters and Constraints== | |

+ | ''Various standard methods of parametrics and constraints available in CAD Programs ( CATIA as a case study )'' | ||

+ | ===Parametrics=== | ||

+ | #Point | ||

+ | ##Coordinates | ||

+ | ##On Curve | ||

+ | ##On Plane | ||

+ | ##On Surface | ||

+ | ##Circle/Sphere Centre | ||

+ | ##Tangent on Curve | ||

+ | ##Between (2 points) | ||

+ | ##Extremum | ||

+ | ##Extremum Polar | ||

+ | #Line | ||

+ | ##Point-Point | ||

+ | ##Point-Direction | ||

+ | ##Angle/Normal to the curve | ||

+ | ##Tangent to the Curve | ||

+ | ##Normal to the surface | ||

+ | ##Bisecting | ||

+ | #Plane | ||

+ | ##Offset from plane | ||

+ | ##Parallel through Point | ||

+ | ##Angle/Normal to Plane | ||

+ | ##Three points | ||

+ | ##Two Lines | ||

+ | ##Point and Line | ||

+ | ##Planar Curve | ||

+ | ##Normal to Curve | ||

+ | ##Tangent to Surface | ||

+ | ##Equation | ||

+ | ##Mean through points | ||

+ | #Axis | ||

+ | #Polyline | ||

+ | #Circle | ||

+ | #Corner | ||

+ | #Connect Curve | ||

+ | #Conic | ||

+ | #Spline | ||

+ | #Helix | ||

+ | #Spiral | ||

+ | |||

+ | ===Constraints=== | ||

+ | #Distance | ||

+ | #Length | ||

+ | #Angle | ||

+ | #Radius/Diameter | ||

+ | #Semimajor axis | ||

+ | #Semiminor axis | ||

+ | #Symmetry | ||

+ | #Midpoint | ||

+ | #Equidistant point | ||

+ | #Fix | ||

+ | #Coincidence | ||

+ | #Cocentricity | ||

+ | #Tangency | ||

+ | #Parallelism | ||

+ | #Perpendicular | ||

+ | #Horizontal | ||

+ | #Vertical | ||

+ | #Angle with axis | ||

+ | |||

+ | ==Notes== | ||

+ | |||

+ | ===Object Overlay=== | ||

+ | ===Extensibility=== | ||

+ | ===Interoperability=== |