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Found 39 results

  1. Wind Tunnel / Vector Field Masking

    Hi, I love the "wind tunnel direction" feature in the sparse solver, and I would like to find a way to mask it's effect. I know this is just a vector field node with "External Direction" set to a given value, but I don't know how to apply a mask to it (say I'm simulating a chimney with smoke rising out from the top. I wouldn't want the wind inside my chimney). I can do this inside the gas wind node or with any other force node. The problem is: none of them look nearly as good as the "External Direction" option in the vector field node! (with gas wind being the worst). I've tried using the "Sop Vector Field" node, and plugging in a sop field with the same value to what an "External Direction" value might be. It kinda works, but not quite. The result is not the same, and I noticed that the velocity field is getting incorrectly updated. (it flashes in and out of active areas when "activated") - also it's slower I hope there is a Gas DOP expert who can help me. Basically what I want, is a wind that looks as natural as the "Wind Tunnel / External Direction" but with the ability for applying masking (and other stuff if possible). Thank you so much, if you actually read this. Thank you even more, if you can help Best Regards, Asger Mortensen.
  2. Hello. I'm struggling with changing vector direction inside a solver. In the file attached there is a point that reads vector attribute of a nearpoint and uses it in order keep on moving. The movement is done in solver. The problem is that it can after doing a "step" the point can take a new vector that is opposite to it's current direction and "step back". It returns to previous position where it gets a former "go ahead" vector and does a "step forward" and repeats the whole vector change and "back and forth" movement on and on. Inside the solver I try to compare vectors of previous and current frame and build a condition - if they are opposite let the point go down {0,1,0}; But no matter how I try it doesn't work. If someone can help me... SOLVER_problem.hipnc
  3. Mask a velocity volume with an object

    Hi everyone, I have a velocity volume working well to advect a vellum sim, by pulling the objects towards the normals of an object. However I'd like to remove all velocity values from within the object, so that once they've been pulled in and "captured", that they can then move freely within the shape of that object. The object is not being fed into the vellum sim for collisions. Is it a matter of doing something like, multiplying the velocity by the inverse of the density? I tried this but couldn't quite get it right, I'm not sure if I'm missing something. Thanks in advance for any help! VelocityRemoveInside_Test.hiplc
  4. Hi guys, I can't make motion vector working in my scene even with a wrangler point to activate it.. Any help? Thank you. MotionVector.hip
  5. Hi all, Noob question... I want to read the 3 components of a specific vector that belongs to a vector array as shown in attached screenshot I don't know where and in which format I have to put the point index and vector index. someone know how to do that ? thank you Alex
  6. Thank you, Karsten Schmidt. Happy New Year https://github.com/thi-ng/vexed-generation
  7. vector on detail (VEX)

    Hi everybody I want to use the "detail" function as an expression in a node parameter to read a vector component. detail("../sourceData","color.r",0) but it does not work. I tried "color.0", same result when I use just "color", it reads something, an average could be, anyway I just want to read one component of a vector value. how can I do that? thanks you.
  8. Hi, How could I measure vector distance to another surface like you see here. Not just closest point distance, but distance following the vector. I would like to use this as length point attribute in hairgen to control the shape of groom with geo. Cheers Janis Vector_length.hip
  9. Geodesics in Heat

    Hi everyone! I've made an illustration video-tutorial about the Heat Method application to point clouds by Keenan Crane et al, Yang Liu et al and others.
  10. Hello everyone, I have created few videos to introduce vectors and matrices in a fun way, with lots of real-world examples. Please go through them and I would love to get a feedback. Intro to Vectors | An Idiot's Guide to Vectors and Matrices, Part 1 Intro to Matrices | An Idiot's Guide to Vectors and Matrices, Part 2 Advance Operations | An Idiot's Guide to Vectors and Matrices, Part 3 Depending on the feedback, I am planning to create few Houdini specific videos as well.
  11. UV from vector file

    Hey. My idea is to create a uv in Illustrator and transfer same uv on geometry object. I try to solve it myself, but now i need your help/some idea. My problem is wrong rotation island on target uv model. I try sort points, primitives and my other idea didnt work. (ofc I dont want fix uv islands by hand) I cleaned my mad project for you and attached project files here (project, vector uv file and texture for experiments) Thanks for your answers. //add The main problem i think wrong sorting vertices i cant solve it. If you unlock "sort" node in my project you see primitives was sorted fine (i hope) I think new map will be more useful (testUV_02.jpg) //new HoudiniTestUV.hipnc testUV_01.ai
  12. Hi there. I am struggling with setting up the following: I have 2 points and I need to create a position/rotation vector from them to attach a new geometry onto the vector. I have got to the point where I have the new object aligned with the vector and I get a correct position and rotation, however I also get a random rotation along the object's own axis. (in an attached file it's the tube which is randomly rotating around it's own X axis. Any help would be appreciated, see the attached set up in the file. Many thanks! Adrianna vector_01.hipnc
  13. magnet force on two directions

    hello! I am having trouble making gravity work in two directions. Basically the world is a tube and I want objects to magnet/have a gravity like force along the Z and Y axis but not on the X axis. I attached my hip file and a picture. Any help would be great! Thank you! tube_attractor.hip
  14. Hi, I compute the velocity on an animated point and I copy a geometry on it which inherits the velocity but of course is not correct as every point now has the exact same vector. How can I realign the existing velocity in the geometry using vex without having to recompute it? I have attached an example hip. orientvelocity.hipnc
  15. How to Calculate @w to Aim RBD Object

    As I'm just starting to understand quaternions and orientation in Houdini, I'm not sure how complicated this is to achieve. I could be completely over thinking it. Ultimately I would like to create a force in dops to rotate the packed object to its current direction of motion, or it's velocity. Modifying @w seems to be the best way to do that. For a first step, I'm trying to make a setup that takes a rbd packed object and rotate it back to it's original orientation. While it technically does that, it doesn't do it logically. It flips around its axis in bizarre ways. As I understand, it's behaving erratically because it's trying to rotate around all of its axes at the same time. This is the code I'm using in a pop wrangle node: vector qToE(vector4 q_value){ float q_0 = q_value.w ; float q_1 = q_value.x ; float q_2 = q_value.y ; float q_3 = q_value.z ; vector out = {0,0,0} ; out.x = atan2(2*(q_0*q_1+q_2*q_3), (1-2*(q_1*q_1+q_2*q_2))) ; out.y = asin(2*(q_0*q_2-q_3*q_1)) ; out.z = atan2(2*(q_0*q_3+q_1*q_2), (1-2*(q_2*q_2+q_3*q_3))) ; return out ; } v@euler = qToE(@orient); @w = -v@euler*1*{1,1,1}; This is where I got the quaternion to euler function: I've attached my houdini file to this post. If anyone has any tips, I'd be very happy to hear them! Thanks! orient_rotate_v01.hip
  16. FGA Sequence Export....

    FGA Sequence Export.... I am using "GitHub Game Development Toolset" for FGA output. However, the included "rop_vector_field" can output only one frame. I want to know export FGA sequence. For example, how to output from 1f to 100f. Thanks...
  17. Hi all ! I'm struggling with an addpoint function, I'd like to use a variable to declare a point but it seems that's not allowed… What is the proper way to do this ? My code in a pointwrangle : float height = fit(rand(@seed, @ptnum), 0, 1, 0.4, 0.55); addpoint(0, {0,height,0}); if I put a 1 instead of "height" it creates the point perfectly well :/ Thank you for your help !
  18. In Vex, I'm trying to find a signed angle between two vectors i.e. an angle which treats one vector as a "base" and the other as a rotating "clock hand", so that I get positive angle for a concave angle between the two (0-180 deg) and a negative angle for a convex angle between the two (180-360 deg). The dot product on normalized vectors gives me the angle, but it's symmetric. Is there a trick that gets me the sign?
  19. I'm trying to control the normal of a single point. I want to use normals to visualize vectors that i will convert to velocity later. I've reduced my experiment to a single point to hopefully simplify things. I'm trying to make the normal point in a truly random direction for each frame. I tried this: float x = fit01(rand(ch("seed1")),-1,1); float y = fit01(rand(ch("seed2")),-1,1); float z = fit01(rand(ch("seed3")),-1,1); @N = set(x,y,z); which gave me a random direction with in a disk. If i substitute @N for @v and feed this into a popnet that uses inherited vel i get particles in a plane. see attached image. If I control each component of the vector leaving two at 0 and setting the third between -1 and 1 i can point the normal in any direction. I can't figure out how to get houdini to randomly set the normals direction in all directions. Help appreciated.
  20. (Novice) Align a selection to point

    Very simple operation required: I need to align all points to the vertical axis occupied by a single point. (align points to the vertical axis of the point highlighted) There has to be a simple method for this. Thanks in advance
  21. Hello!, Let's say I have a rotating cube, a grid floor and a direct light projecting the shadow of the cube into the floor.. how can I get the motion vector of this projected shadow? , I already know how to get the vectors of the cube but it's shadow is a mistery.
  22. Hello, Trying to read a vector array from another point at a certain index. From my understanding of Houdini something like this should work. vector tempArray[] = point(0,"vectorArrayAttrib",pointToReadFrom); vector v = tempArray[index]; Unfortunately this method is returning an empty array from the point() function. If this is not the right way to go about doing this please let me know. Any help welcomed. Thanks.
  23. Hello,I'm attempting to create the slitscan/timeshift effect. I'm creating a vector array in a for loop, each loop has an attrib from map and a wrangle that appends Cd to a vector array. It works when the attrib from map is always reading from the same file. When I change the attrib from map file read expression to anything that has to do with $F or the meta nodes iteration Houdini crashes. I have a test scene that has documentation and even nodes setup to create test frames to work with.If it is a matter of the way that multiple files cannot be read at once please let me know. If someone knows of a better way to read from multiple files at once and/or achieve this effect please let me know. I'm aware that after effects has this effect and uses gradients to determine which frame to look up color from. While that method is great, I'd like to be able to write the gradients/lookups in vex to achieve results. Any help greatly appreciated. -T concept_025_slitScan_v001.hiplc
  24. retarget or recompute vector

    Hi everyone, I try to figure out how to retarget a vector (v in that case) in particle trails. I explain: i got master particles who trail other particles in space, i inherit the master "v" to achieve a motion blur at render time, to avoid to much substep that way i got smooth line at low calculation cost. but i need to slightly noise the trails to achieve a "moving tentacles" look. Here is the problem when i apply the noise, obviously my "fake" v vector is not aligned anymore, it's stepped... i tried to recompute the vector with the help of id, but since my emission is not constant ( i shot on frame 5, frame10, frame15 etc..)the incrementation of the id in not constant to...I tried basic vector arithmetic, but i don't get results i need...I join a hip file, does anyone got an idea??? thanks by advance. Best H PS:excuse my english, I'm French... RecomputVelTest.hip
  25. Hi So basically I have a vector and an obj, how can I make the obj face the vector by specifiyng the front axis of the obj? (front, side, up) Is there a traditional way to do this? Because Im trying to do this myself through Vex and some transforming operations.. Example:
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