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  • Oct 21 19:06
    Aposhian starred boostorg/geometry
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tinko92
@tinko92
Thanks for the ideas. It sounds interesting and useful (I think, a hit-by-ray-first query could also have utility in my usage of the rtree) but also like a bigger undertaking than I had originally in mind. I'll think about it (later).
Ayush Gupta
@ayushgupta138
are project ideas for gsoc 2021 published for boost geometry? I was only able to see project ideas for previous years.
Mateusz Łoskot
@mloskot
None at https://github.com/boostorg/wiki/wiki/Google-Summer-of-Code%3A-2021
Students are free to suggest projects of their own interest though
Mateusz Łoskot
@mloskot
By the way, the project has mailing list
Siddharth Kumar
@Siddharth-coder13
Hello mentors, I have proposed a new project for GSOC 2021, https://lists.boost.org/Archives/boost/2021/03/251051.php
@mloskot @vissarion I would like to discuss about the project, if this one sounds good.
Mateusz Łoskot
@mloskot
Three words: search web first
Ayush Gupta
@ayushgupta138
is there any slack channel for boost geometry?
Mateusz Łoskot
@mloskot
No, but there are #boost and #boost-user and #boost-gsoc
Siddharth Kumar
@Siddharth-coder13
Hey @vissarion, here is my proposal draft as suggested by you https://docs.google.com/document/d/1NJ6MYRphIHJNizQqQoKYxCOijkFh6STIIAUgP98jafs/edit?usp=sharing it would be great if you provide some feedback.
Vissarion Fisikopoulos
@vissarion
thanks for sharing @Siddharth-coder13
shadymohamedamin
@shadymohamedamin
Hello all, I am Shady, Faculty of Engineering, Department of Computer Engineering, and I want to participate in the Google Summer of Code Boost Organization, so I need some suggestions about how I begin and what is the issue and buggs that i will begin with it to solve it?
Thanks
I am very interested in participating in google summer of code
shadymohamedamin
@shadymohamedamin
I have working and practical experience working in C,C++, Python, dart,matlab,prolog, etc. with knowledge of mathematical concepts like Linear Algebra, discrete math , . etc. I am interested in contributing to Boost and apply for GSoC. Will be highly grateful for guidance on beginning processes in contributing to Boost.
@vissarion @awulkiew @mloskot
Mateusz Łoskot
@mloskot
@shadymohamedamin Search the web, read archives of this channel, mailing lists. Surely, you can't be the only one who asked such questions lately
Ayush Gupta
@ayushgupta138
Hello everyone,
I wanted to know about the implementation of Polyhedral surface in Boost.Geometry. Since my GSoC 2021 project proposal is based on Polyhedral surfaces, I wanted the know the interface and implementation of the same. Since there are not much details in https://portal.ogc.org/files/?artifact_id=18241, should I assume the implementation to be more or less as in https://doc.cgal.org/latest/Polyhedron/index.html ? It would be really helpful if someone could provide some material on Polyhedral Surface interface.
Ayush Gupta
@ayushgupta138
@mloskot @vissarion @awulkiew?
Mateusz Łoskot
@mloskot
Mateusz Łoskot
@mloskot
The OGC spec and SQL MM spec and PostGIS implementation is also a good place to look at
Ayush Gupta
@ayushgupta138
As per the https://postgis.net/docs/manual-2.0/ST_GeometryN.html , a polyhedron is defined as a set of 3d planar polygons. But unlike polygon, a polyhedron cannot be represented only as set of 3d planar polygons. For example, their incidence relation also has to be specified, which could be inferred in the case of polygons from the point order.
Ayush Gupta
@ayushgupta138
@mloskot @vissarion please correct me if I am wrong.
Mateusz Łoskot
@mloskot

A PolyhedralSurface is a simple surface, consisting of some number of Polygon patches or facets. If a PolyhedralSurface is closed, then it bounds a solid.

If you read the OGC spec you should find more answers

From The PostGIS in Action book at https://livebook.manning.com/book/postgis-in-action-third-edition/chapter-2/v-15/36

Float a bunch of polygons in three-coordinate space and glue them together at their edges, and you’ll form a patchwork referred to as a polyhedral surface. Although polygons make up both multipolygons and polyhedral surfaces, there is one fundamental difference: polygons in multipolygons can’t share edges; polygons in a polyhedral surface almost always do. There are two other notable restrictions in the construction of polyhedral surfaces: polygons can’t overlap, and each edge can be mated with at most one other edge.

Vissarion Fisikopoulos
@vissarion

But unlike polygon, a polyhedron cannot be represented only as set of 3d planar polygons.

Does that mean that if the user gives a set of polygons in 3d space then this could correspond to more than one polyhedral surface?

Mateusz Łoskot
@mloskot
It's worth to note, Polyhedral Surface is not necessarily a Polyhedron
Vissarion Fisikopoulos
@vissarion
Thanks @mloskot let me add this page https://jeffe.cs.illinois.edu/compgeom/ it is quite old but packed with useful information
Mateusz Łoskot
@mloskot
:thumbsup:
Siddharth Kumar
@Siddharth-coder13

It's worth to note, Polyhedral Surface is not necessarily a Polyhedron

Polyhedron is a special case of polyhedral surfaces when it is closed.

Mateusz Łoskot
@mloskot
@Siddharth-coder13 Yes, it's important to agree on definition of the Polyhedral Surface first, then dive into special cases.

However, my point was that @ayushgupta138 comment here :point_up: March 22, 2021 4:59 PM suggested he is misunderstanding the difference and using Polyhedral Surface and Polyhedron interchangeably, what is wrong.

Why I think @ayushgupta138 mismatches these two?
Because the page he referred https://postgis.net/docs/manual-2.0/ST_GeometryN.html does not even use word 'Polyhedron', but he is asking his question about Polyhedron referring to that page.

IOW, communication needs to be precise to avoid side discussion on what is what.

Siddharth Kumar
@Siddharth-coder13
👍
Ayush Gupta
@ayushgupta138

However, my point was that @ayushgupta138 comment here :point_up: March 22, 2021 4:59 PM suggested he is misunderstanding the difference and using Polyhedral Surface and Polyhedron interchangeably, what is wrong.

Yes, I used polyhedron and polyhedral surface interchangeably and it was my fault for doing so. Thanks to @mloskot and @vissarion the difference is clear to me now.

shadymohamedamin
@shadymohamedamin
I want to contact with the mentors (david bellot and cem bassoy)
Boost.ublas
And i want the irc channel to discuss the project with them
Very thanks ♥️
@mloskot
Mateusz Łoskot
@mloskot
@shadymohamedamin First, you want to learn how to search the web. There are materials and instructions that address your questions, on Boost site, wiki, mailing list archives.
Brett McDonald
@bfmsoft
OK, been 35 years since took geometry ;) here is my problem. cx,cy is starting point and dx,dy is destination point. Circle is centered on cx,cy with radias r. What is the equation to file the point the line from cx,cy to dx,dy that intercepts the circle? I want the x,y of the intersection point.
Adam Wulkiewicz
@awulkiew
@bfmsoft If your line starts at the center then what you really want is to get point at distance r into the direction of D. So with vectors this will be: C+(D-C)/|D-C|*r, where C is point (cx, cy), D is point (dx, dy), (D-C) is vector from point C to point D, |D-C| is the length of this vector and (D-C)/|D-C| is this vector normalized (it has length 1). So if you multiply this vector by r then you get a vector of length r having the same direction as your line.
Ayush Gupta
@ayushgupta138
is no one selected for Boost.Geometry in GSoC?
Brett McDonald
@bfmsoft
image.png
I looking for something that be close to that basically y = "something(x)" I understand I can offset for the first part that is straight. I was looking for something like a dog leg that drops off quickly and approaches the line slowly?
Adam Wulkiewicz
@awulkiew
@bfmsoft You mean something like an exponential function: y = a^(-x+b) ?
@bfmsoft This is a chat of Boost.Geometry C++ library. It's not for discussing general math problems. There are other, better places for that, e.g. math.stackexchange.com
Adam Wulkiewicz
@awulkiew

is no one selected for Boost.Geometry in GSoC?

@vissarion what's with GSoC this year?

Vissarion Fisikopoulos
@vissarion

is no one selected for Boost.Geometry in GSoC?

@vissarion what's with GSoC this year?

Boost.Geometry will not mentor any student for GSoC-2021