I am using the open source program triangle.c (A Two-Dimensional Quality Mesh Generator and Delaunay Triangulator) which can be found here. I have to use this program to mesh a 2d circle and then rotate it to get 3d mesh of a sphere. Once I specify the points on the boundary, the program adds additional nodes inside the region and generates triangular meshes. However I would like to avoid adding nodes on the axis about which I want to rotate. Is there a good way to achieve this?
the 2d geometry i want to mesh
Related
I want to know the basic idea of creating 2d views of a 3d geometry in cads like autocad, solidworks, and etc..
Here, I listed some basic ideas that I had reached now.
Which method are they used ? or any method I didn't listed ?
idea A:
first, to render every single face to a plane space.
then detect the boundaries of faces.
do something magic that can recognize the 2d curves from the boundary pixels .
do something magic again to recognize which segments of curves should be hiddened.
construct a final view from lines and curves generated from above steps.
idea B:
they create projection rules for every type of surface with boundary wires, like plane, cylinder, sphere, spline. And thoes rules can be used in all projection angles.
then, implement projection rules for every face, and finally they got a view of many curves.
to iterate all curves generated from step 2, and check the visibility of the curve.
construct a final view.
idea C:
first, tessellate every faces to many triangles.
then, found boundaries from triangles for every faces.
then, we got many polylines from step 2.
to iterate all polylines generated for every faces, and check the visibility of the polylines.
construct a final view.
I found a solution, it follows this way:
tessellate every face and edge to triangles and segments.
project all those triangles and segments to a plane.
then choose a suitable resolution to construct those projected triangles and segments to pixels with a height parameter.
found contours for every face and edge from those pixels.
set visible value for every pixel on that contour depends on the height parameter of a total pixel's view.
reconstruct line, circle, and polylines from pixels.
I tested this method for some models, and works well. below is one of them:
How can I adapt a geometry (a box geometry to start with) to another one? I am looking for an effect like the one in the picture
where the cyan part was originally a box and then it got "adapted" to the plane and over the red part.
This is possible in some software packages (Modo, for example) but I'd like to do it in webGL/three.js
Consider modifying mesh geometry.
That implies for good results mesh will need to have high polygon count.
If you want to hug a simple shape (box, sphere) - vertex displacement can be sufficient:
Pass your red shape's parameters as uniforms when drawing blue shape
For any blue shape vertex find if it is inside or red shape and offset vertex position if needed
Choosing offset direction as closest face normal of red shape should be ok
That will give just visuals, if you need more robust solution - generate new geometry entirely on cpu on demand.
For example:
Loop through all vertices and offset them, mark offseted vertices
Additionally loop to relax hard edges
I suspect real algorithms from 3d modelling software are more complex.
Is there any simple algorithm like Voronoi diagram to divide any rectangular plane to triangles, eventually, using # of pre-defined points.
To be honest, I have to write a very simple fragment shader like this.
Theoretically, this Voronoii shader could be 'upgraded' by Delaunay triangulation
but wanna find the more elegant solution.
The first thing that comes to my mind is to create n random points (with specific seed) to fill a cylinder volume. The triangle points will be intersection of lines between those points and plane going through the axis of cylinder. The animation would be simply done by rotating the plane ...
I see it something like this:
So the neighboring points should be interconnected with each other. Forming tetrahedrons that fills the volume of the cylinder. So create uniform tetrahedron grid and add random noise to the points position (with specific seed).
This whole task is very similar to rendering cross section of 4D mesh see:
4D rendering techniques
As the 4D simplex is also tetrahedron. The only diference is you are in 3D and cutting by 3D plane.
You can reverse-engineer this example shadertoy.com/view/MdfBzl
like I did. Thanks to mattz.
Newbie to three.js. I have multiple n-sided polygons to be displayed as faces (I want the polygon face to be opaque). Each polygon is facing a different direction in 3D space (essentially theses faces are part of some building).
Here are a couple of methods I tried, but they do not fit the bill:
Used Geometry object and added the n-vertices and used line mesh. It created the polygon as a hollow polygon. As my number of points are not just 3 or 4, I could not use the Face3 or Face4 object. Essentially a Face-n object.
I looked at the WebGL geometric shapes example. The shape object works in 2D and extrusion. All the objects in the example are on one plane. While my requirement is each polygon has a different 3D normal vector. Should I use 2D shape and also take note of the face normal and rotate the 2D shape after rendering.
Or is there a better way to render multiple 3D flat polygons with opaque faces with just x, y, z vertices.
As long as your polygons are convex you can still use the Face3 object. If you take one n-sided polygon, lets say a hexagon, you can create Face3 polygons by taking vertices numbered (0,1,2) as one face, vertices (0,2,3) as another face, vertices (0,3,4) as other face and vertices (0,4,5) as last face. I think you can get the idea if you draw it on paper. But this works only for convex polygons.
I am trying to make a quadrilateral mesh from a surface mesh (which is mostly triangular) generated by Mathematica. I am not looking for high quality mesher but a simple work around algorithm. I use GMSH for doing it externally. We can make use of Mathematic's CAD import capabilities to generate 3D geometries that are understood by the Mathematica kernel.
We can see the imported Geometry3D objects and the plots of number of sides in each polygons they consist of. It become visible that the polygons that form the mesh are not always triangles.
Name3D=RandomChoice[ExampleData["Geometry3D"][[All,2]],6];
AllPic=
Table[
Vertex=ExampleData[{"Geometry3D",Name3D[[i]]},"VertexData"];
Polygons=ExampleData[{"Geometry3D",Name3D[[i]]},"PolygonData"];
GraphicsGrid[
{{ListPlot[#,Frame-> True,PlotLabel->Name3D[[i]] ]&#(Length[#]&/#Polygons),
Graphics3D[GraphicsComplex[Vertex,Polygon[Polygons]],Boxed-> False]}}
,ImageSize-> 300,Spacings-> {0,0}],
{i,1,Length#Name3D}];
GraphicsGrid[Partition[AllPic,2],Spacings-> {0,0}]
Now what I am looking for is an algorithm to form a quadrilateral mesh from that polygon information available to MMA. Any easy solution is very much welcome. By easy solution I mean which is not going to work in a very general setting (where mesh constitutes of polygons with sides more than 5 or 6) and which might be quite inefficient compared to commercial software. But one can see that there are not many quadrilateral surface mesh generator available other than few expensive commercial one.
BR
this will produce quads regardless of the input topology:
insert one vertex in the center of each face
insert one vertex at the midpoint of each edge
insert edges connecting each face's center vertex with it's edges' midpoint vertices