I have a 3D triangulated surface. Nodes and Conn variables store the coordinates and connectivity of the triangles. At each vertex, a scalar quantity, S, and a vector with three components, V, are stored. These data are time-dependent. Also, my geometry does not change over time and I have one surface for all the timesteps.
How should I approach for writing a VTK file that has the transient data over this surface? In other words, I want to write the value of S and V at different timestep on this 3D surface in a single VTK file. I ultimately want to import this VTK file into Paraview for visualization. vtkTemporalDataSet seems to be the solution for me but I could not find an example on how to write an ASCII or binary file for this VTK class. Could vtkPolyData somehow be used to define time so that Paraview knows the transient nature of my dataset? I would appreciate any help or comment.
The VTK file format does not support transient data. However, you can write a series of files that ParaView will interpret as a time sequence. This will work fine with poly data in the VTK file. The file series is defined as files of the same name with a number identifier in them. For example, if you have a series of files named:
MyFile_000.vtk
MyFile_001.vtk
MyFile_002.vtk
ParaView will group these files together in its file browser and when you read them together, it will treat them as a file sequence with 3 time steps.
The bad part of this representation is that you will have to replicate the Nodes and Conn in each file. If that is a problem, you will have to use a different file format that supports multiple time steps using the same connection information (such as the Exodus II file format).
Related
how to convert the image into object file like as .obj or .ply . I need some code written in visualization toolkit and c++.
Thanks
Image data is pixel data and .obj/ .ply or for that matter .stl is 3D geometry data with Point and Cell (for .obj Cell is Triangle) information.
Your question is not clear, but to give you some steps -
First, you need to identify how would you convert the pixels into points? vtkImageDataGeometryFilter might be of help here. Although it might not be sufficient as you will also need triangles data.
Once you get vtkPolyData from image data, you can write this data to STL or OBJ or PLY format. You can use following VTK classes for that
vtkSTLWriter, vtkOBJWriter and vtkPLYWriter.
STL is the most popular 3d model file format for 3d printing. It records triangular surfaces that makes up a 3d shape.
I read the specification the STL file format. It is a rather simple format. Each triangle is represented by 12 float point number. The first 3 define the normal vector, and the next 9 define three vertices. But here's one question. Three vertices are sufficient to define a triangle. The normal vector can be computed by taking the cross product of two vectors (each pointing from a vertex to another).
I know that a normal vector can be useful in rendering, and by including a normal vector, the program doesn't have to compute the normal vectors every time it loads the same model. But I wonder what would happen if the creation software include wrong normal vectors on purpose? Would it produce wrong results in the rendering software?
On the other hand, 3 vertices says everything about a triangle. Include normal vectors will allow logical conflicts in the information and increase the size of file by 33%. Normal vectors can be computed by the rendering software under reasonable amount of time if necessary. So why should the format include it? The format was created in 1987 for stereolithographic 3D printing. Was computing normal vectors to costly to computers back then?
I read in a thread that Autodesk Meshmixer would disregard the normal vector and graph triangles according to the vertices. Providing wrong normal vector doesn't seem to change the result.
Why do Stereolithography (.STL) files require each triangle to have a normal vector?
At least when using Cura to slice a model, the direction of the surface normal can make a difference. I have regularly run into STL files that look just find when rendered as solid objects in any viewer, but because some faces have the wrong direction of the surface normal, the slicer "thinks" that a region (typically concave) which should be empty is part of the interior, and the slicer creates a "top layer" covering up the details of the concave region. (And this was with an STL exported from a Meshmixer file that was imported from some SketchUp source).
FWIW, Meshmixer has a FlipSurfaceNormals tool to help deal with this.
I am doing a project in which I want to embed images into a .wav file so that when one sees the spectrogram using certain parameters, they will see the hidden image. My question is, in C++, how can I use the data in a wav file to display a spectrogram without using any signal processing libraries?
An explanation of the math (especially the Hanning window) will also be of great help, I am fairly new to signal processing. Also, since this is a very broad question, detailed steps are preferable over actual code.
Example:
above: output spectrogram;
below: input audio waveform (.wav file)
Some of the steps (write C code for each):
Convert the data into a numeric sample array.
Chop sample array into some size of chunks, (usually) overlapped.
(usually) Window with some window function.
FFT each chunk.
Take the Magnitude.
(usually) Take the Log.
Assemble all the 1D FFT result vectors into a 2D matrix.
Scale.
Color the matrix.
Render the 2D bitmap.
(optional) (optimize by rolling some of the above into a loop.)
Add plot decorations (scale, grid marks, etc.)
I have a 3D model as mesh structure or in .stl/.obj format which I converted to voxels using binvox voxelization tool. Using a Java program, I have done some processing on the voxel grid thus obtained. Now, I wish to covert this voxelized model back into a "smooth" mesh structure (or any other format), which can later be exported to .stl or .obj format.
Can someone suggest how can I achieve the last part, i.e. converting the voxel grid into some format for retrieving back the "smooth" surfaces ? Any help, including pointing to existing tools, or relevant theory in this direction will be appreciated.
Give a try to Marching Cubes algorithm. See http://paulbourke.net/geometry/polygonise/ for more details.
I working on program (fortran90), which computes an magnetic field of some static set of wires with electric current. Its output is a magnetic field vectors in many points as file with columns "x,y,z,v_x,v_y,v_z). I able to plot this with gnuplot, e.g.:
But now I want to rewrite program to output isosurfaces (surfaces at which modulus of magnetic field vector is constant), like this (it is found in internet and don't correspond to first image)
Can I do this as second program or with using utility, which will convert my file with 6 columns into ... something format which can be drawn as surface set. Another way of doing this, as I think, is to rewrite first program to compute isosurface directly. Please, recommend me which way is better and how actually I can do this.
I think MathGL can do it easily. It is cross-platform GPL plotting library which have Fortran interface too. Here you can use a sequential call of vector fields and isosurface plotting.