# Question about Estimation of Local Differential Properties

9 messages
Open this post in threaded view
|

## Question about Estimation of Local Differential Properties

 Hello - I'm looking to use the jet-fitting algorithm to compute the principal curvature and directions at various non-vertex points of a (triangular mesh) i.e. my points of interest lie on the faces of a mesh, and by definition, do not coincide with its vertexes. My question however concerns the method used by the implementation of the jet-fitting algorithm in this case. I would like to confirm if the jet-fitting algorithm uses an (a) interpolation or (b) approximation approach to compute the differential properties at such no-vertex points -- the former would be preferred. I'm aware that this issue was discussed on page 12 of "Jet fitting 3: A Generic C++ Package for Estimating the Differential Properties on Sampled Surfaces via Polynomial Fitting", but I found the reading a bit confusing probably because I'm only just learning the algorithm. Thanks, - Olumide -- You are currently subscribed to cgal-discuss. To unsubscribe or access the archives, go to https://lists-sop.inria.fr/wws/info/cgal-discuss
Open this post in threaded view
|

## Re: Question about Estimation of Local Differential Properties

 Hello, i summarize here the discussion we had by phone: you can use interpolation with the jet fitting if you give exactly   the nb of points that correspond to the nb of constraints. Then, by default, the differential quantities returned are those   computed at the projection of the first point you have given on the   fitted polynomial surface. If you want to compute the quantities for another point p, and you   dont want this point to be taken into account to do the fitting   (either-wise just give this point first and you are done); you can   just project this point on the fitted surface (that is given by the   monge form in the monge coordinate system) and compute the diff   quantities by classical diff geo formula. I may consider adding this functionality in the future ... best Marc On 28 , May , 2008, at 06:42 , Olumide wrote: > Hello - > > I'm looking to use the jet-fitting algorithm to compute the   > principal curvature and directions at various non-vertex points of   > a (triangular mesh) i.e. my points of interest lie on the faces of   > a mesh, and by definition, do not coincide with its vertexes. > > My question however concerns the method used by the implementation   > of the jet-fitting algorithm in this case. I would like to confirm   > if the jet-fitting algorithm uses an (a) interpolation or (b)   > approximation approach to compute the differential properties at   > such no-vertex points -- the former would be preferred. > > I'm aware that this issue was discussed on page 12 of "Jet fitting   > 3: A Generic C++ Package for Estimating the Differential Properties   > on Sampled Surfaces via Polynomial Fitting", but I found the   > reading a bit confusing probably because I'm only just learning the   > algorithm. > > Thanks, > > - Olumide > > > -- > You are currently subscribed to cgal-discuss. > To unsubscribe or access the archives, go to > https://lists-sop.inria.fr/wws/info/cgal-discuss-- You are currently subscribed to cgal-discuss. To unsubscribe or access the archives, go to https://lists-sop.inria.fr/wws/info/cgal-discuss
Open this post in threaded view
|

## Is there an existing function to get the bbox of a polyhedron_3

 hi, I want to get the (axis aligned) bounding box of a given polyhedron_3. I don't know if there is an existing funtion to do this. thanks for any hints. B/Rgds Max -- You are currently subscribed to cgal-discuss. To unsubscribe or access the archives, go to https://lists-sop.inria.fr/wws/info/cgal-discuss
Open this post in threaded view
|

## Re: Is there an existing function to get the bbox of a polyhedron_3

 Max wrote: > hi, > > I want to get the (axis aligned) bounding box of a given polyhedron_3. > I don't know if there is an existing funtion to do this. > > thanks for any hints. > > B/Rgds > Max > Hi Max, There is no bbox() member function that caches and updates the bbox whenever you change the Polyhedron_3. The most compact piece of code for computing the bbox in linear time looks like this #include Polyhedron_3 poly; CGAL Bbox_3 bb  = CGAL::bounding_box(poly.points_begin(), points_end()).bbox(); andreas -- You are currently subscribed to cgal-discuss. To unsubscribe or access the archives, go to https://lists-sop.inria.fr/wws/info/cgal-discuss
Open this post in threaded view
|

## Re: Re: Is there an existing function to get the bboxof a polyhedron_3

 >Hi Max, > >There is no bbox() member function that caches and updates >the bbox whenever you change the Polyhedron_3. > >The most compact piece of code for computing the bbox in linear time >looks like this > > >#include > >Polyhedron_3 poly; > > >CGAL Bbox_3 bb  = CGAL::bounding_box(poly.points_begin(), points_end()).bbox(); > > >andreas Hello andreas, Thank you very much for your quick and detailed reply. That's enough for my current demand. B/Rgds Max -- You are currently subscribed to cgal-discuss. To unsubscribe or access the archives, go to https://lists-sop.inria.fr/wws/info/cgal-discuss
Open this post in threaded view
|

## Re: Is there an existing function to get the bboxof a polyhedron_3

 >Hello andreas, > >Thank you very much for your quick and detailed reply. >That's enough for my current demand. > >B/Rgds >Max Just one more question - suppose I have a bunch of bbox_3, what is the convenient way to get the 'union' of them. Thanks and B/Rgds. Max -- You are currently subscribed to cgal-discuss. To unsubscribe or access the archives, go to https://lists-sop.inria.fr/wws/info/cgal-discuss
Open this post in threaded view
|

## Re: Is there an existing function to get the bboxof

 Max wrote: > > Just one more question - suppose I have a bunch of bbox_3, > what is the convenient way to get the 'union' of them. There doesn't seem to be a function that does this. But, using the values of x/y/z-min(), x/y/z-max(), you can easily create a function that does this for your bbox_3 list. Regards, ~ash -- You are currently subscribed to cgal-discuss. To unsubscribe or access the archives, go to https://lists-sop.inria.fr/wws/info/cgal-discuss