This will include loading such meshes from STL files, performing the intersections, as well as visualizing the mesh, lines, and points in VTK.
This will include loading such meshes from STL files, performing the intersections, as well as visualizing the mesh, lines, and points in VTK. In addition, I will present my very own pycaster package which cleanly wraps the VTK parts and allows for cleaner code and added functionality.
However, I should make clear that ray-casting is the natural precursor to ray-tracing as it tells us what part of which object the ray intersects with and provides all necessary information to cast subsequent rays.
I will first demonstrate the approach on a very simple model of a hollow sphere which was designed in Rhino3D and exported to STL. Upon establishing the approach, I will talk about my very own pycaster package which I wrote to wrap the VTK part of the code, simplify the whole process, and provide some additional functionality.
Subsequently, I will repeat the ray-casting process with pycaster on the model of the human skull we extracted and saved as an STL file in the previous post.
Helper-functions As I keep writing new posts I will try my darndest to build upon previously presented snippets in the interest of code-reuse, consistency, and brevity.
The following helper-functions will be used: This function allows me to pass a vtkRenderer object and get an IPython Notebook compatible image output of that render with given dimensions.
This function is very similar to addPoint but instead adds a line with p1 and p2 coordinates using the vtkLineSource class. This function uses the vtkSTLReader class to load the contents of an. GetOutput If there are no points in 'vtkPolyData' something went wrong if polydata.
The mesh is then stored internally in a vtkPolyData object, a pointer to which we retrieve through GetOutput and store under polydata which we eventually return. A point of interest in the above code lies in the usage of the GetNumberOfPoints method of the vtkPolyData class through which we check if the vtkSTLReader object managed to read in anything.
Thus, one should always check that the operation was indeed successful. You can find the corresponding notebook herewhile the STL model of the hollow-sphere can be download here. The only novelty here is the GetProperty method of the vtkActor class. The above code yields the below figure. Preparing and rendering the ray This hollow sphere model is centered around 0,0,0exhibits an outer radius of 25 mm, and an inner radius of 20 mm, resulting in a shell thickness of 5 mm.
Therefore, for the purposes of this example, we set the source and target points of the ray to 50 mm on each side of the the x axis as such: Testing for intersection Now here comes the fun part!
Firstly we need to prepare the OBB tree as follows: We now have a world-class intersection tester at our disposal. We then pass the pSource and pTarget coordinates of the ray along with pointsVTKintersection where the intersection points will be stored.
Notice the code variable which stores the return value of IntersectWithLine? Extracting the intersection point coordinates At this point we have acquired the intersection points which are stored under pointsVTKintersection, an object of vtkPoints type.
This next part of the code is important: GetNumberOfTuples as every point will be stored as a 3-value tuple of the 3D coordinates. We create an empty list under pointsIntersection which will store all those tuples.
Subsequently, we loop through those tuples stored in pointsVTKIntersectionData, acquiring each of them through the GetTuple3 method, appending each tuple in the pointsIntersection list. A simple print shows us those coordinates: The pycaster package Background I wrote pycaster in order to wrap and simplify the VTK functionality you saw above.
The pycaster package is currently being hosted on PyPI under this link, while the repo can be found on BitBucket under this link. The pycaster package really only has a single module, also called pycaster, and contains a single class called rayCaster with methods that are simply wrapping the VTK code you saw above.
Actually, the VTK code you saw above was pretty much copied from pycaster.The idea behind ray casting is to shoot rays from the eye, one per pixel, and find the closest object blocking the path of that ray. Think of an image as a screen-door, with each square in the screen being a pixel.
Writing a Simple Ray Tracer (scratchapixel) Ray tracing a torus. Oct 05, · This entry was posted in Image Processing, Visualization, VTK and tagged IPython Notebook, Python, Ray Casting, Ray Tracing, STL, VTK by somada Bookmark the permalink.
16 thoughts on “ From Ray Casting to Ray Tracing with Python and VTK ”. Writing a Raytracer, and perspective viewing system not displaying properly? Ask Question. Efficiency of perspective projection vs raytracing/ray casting. 3. Writing a Raytracer, and cant get the image to be centred properly?
A first-person engine in lines. by Hunter Loftis twitter email. Today, Where are we casting rays from? That's what the player is all about. We need just three properties: x, y, and direction. Python port by Sean McKiernen. Extended version by Iker Jamardo. Writing a Basic Ray Tracer Source Code We received quite a few emails from readers asking, "Well, if that's so easy to do, can't you provide us with a real example?".
Oct 05, · Ray Casting with Python and VTK: Intersecting lines/rays with surface meshes; 16 thoughts on “ From Ray Casting to Ray Tracing with Python and VTK ” Josh Christianson on October 10, I’ve used your .