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petz

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petz last won the day on November 27 2018

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About petz

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    petz

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  1. "Make circle" SOP?

    please take a look at the attached file. i've slightly modified the old example and now it should work without problems. hth, petz human1.hiplc
  2. Python: Loop delete geometry

    there are a number of different ways how you could do this. for high polycount meshes, however, python might be fairly slow ... please take a look at the attached file. hth. petz landscape_slice_export_1.hiplc
  3. Heightfield Isolines?

    here's another one which might be faster by avoiding the foreachLoop. hth. petz isolines.hipnc
  4. water drops on bottle

    1) the chopnet is used to procedurally adjust the “flowing” speed of the animated point (droplet). on flatter areas it simply gets slowed down. 2a) the curve (following the animated point) uses pscale as an attribute for fading out the size of droplets towards the tail of the curve. 2b) it’s used to delete all points which distance to the curve is above a given threshold 2c) xyzdist() returns the closest position on the prim in parametric coordinates (primuv). in our case it’s a curve and so it returns just one useful value which is u. in other words, it’s the position along the curve. hth. petz
  5. Recompute topology after projection on a plane

    please take a look at the attached file. hth. petz geo_flatten.hipnc
  6. Curvature field

    not exactly sure what you're after but if you want to calculate the gradient of curvature there is no better and easier way than what toadstorm already mentioned ... curv_gradient.hipnc
  7. Recompute topology after projection on a plane

    can't you use triangulate2d for this?
  8. calculating the edge vector is not a problem but you can't store it on edges since houdini doesn't support edges as regular geometry elements. what you could do instead is to use convertLine and do all the computations on prims which you could then lookup by points from the actual mesh. or you could just write all the edge vectors into a detail array. please take a look at the attached file. hth. petz edge_vec.hipnc
  9. due to the use of "remove shared edges" in the divideSop you got always two coincident polygons for every section. you need to delete duplicates and then make sure the normals of remaining prims are pointing into the same direction. instead, you could also set the output of the booleanSop to "seam" and check the curve direction based on point neighbours ... hth. petz
  10. here's a simple one ... hth. petz perpenticular_tangent_1.hipnc
  11. here's another one. it's a simple vex solution which works basically by counting the number of intersections along the curve and the fact that an uneven number means it`s inside an object ... hth. petz curve-boolean.hipnc
  12. Jake's HIPs Don't Lie

    hey jake! well, what you're calculating is not curvature but some curvature-indicating value. this, of course, makes sense since you're relying on normals which are per definition closely intertwined with curvature. but instead of building the covariance matrix you could just do pretty much the same by averaging the normalized normals from surrounding points and calculate the difference to the normal of the current point. however, from the mathematical and geometrical side of things neither this, nor your method has much to do with measuring curvature and the result is most probably off by a large number. (in your case, for instance, it's a min. and max. value of 0.000332 / 0.7385 compared to mean curvature of -107.395 / 204.042). if you want to compute curvature by using eigenvalues you need to compute, for example, the shape operator by computing the jacobian of N, which in this case results in the hessian and finally project it onto the surface. building the covariance matrix of normals doesn't make much sense if you're talking about accurate curvature values. building the shape operator is one of the methods described at houdiniGubbins and no, it doesn't need to be a triangle mesh. fitting a polynomial and computing curvature analytically also doesn't need triangles. in fact it doesn't need any mesh at all and works even on a pointcloud. the same is true if you're computing the curvature tensor based on a simple diffusion distance and search for k1 and k2 in the least squares sense. the most accurate results, however, are possible on a triangular mesh. you're right that curvature computation on meshes is generally problematic but the reason is not because of irregular distances in the one-ring. the main problem is that second order derivatives of piecewise continuous functions are pretty much everywhere null and hence curvature is constant on a triangle. using the edgeTransportSop does not solve this problem. if we are talking about the smooth case, then your idea might makes some sense but on a smooth surface you simply wouldn't need it because here it's easy to compute derivatives. beside that, you would need geodesic distances and not the shortest path distances which the edgeTransportSop calculates... hth. petz
  13. here's another one which is using rigid transformation similar to "extractTransform" but in sops. works also an geometries with points in arbitrary order as long as the pointcount is the same. if that's not the case you could try to use the file in this post: http://forums.odforce.net/topic/28907-wrapping-geo-like-wrap3/?tab=comments#comment-164108 hth. petz pc_match_001_1.hip
  14. Surface Curvature

    depending on your mesh and accuracy there exist numerous different algorithms to compute discrete curvature, all with their pros and cons. i don't think there's a single one which works flawlessly in all situations and for all meshes. anyways, here's a file i've posted a while ago on discord with different implementations. it might be a bit confusing without the conversation we had in the chat but you can just try which algorithm works best for you. (from left to right: classical taubin tensor using integral formula, tensor using euler formula, approximated shape operator, proper shape operator in surface space, polynomial fitting) hth. petz curvature.hipnc
  15. How to planarize dual mesh primitive ?

    your first picture seems to show something like a saddle surface which is partly concave. i don't think that it's geometrically possible to approximate such a surface with convex hexagonal polygons which are also planar and connected. you'll always end up with concave hexagons in your case ...
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