{"topic":{"id":7113,"title":"实验 2.5BVH 光线加速求交：Model 平移存在严重偏移问题","slug":"topic","categoryId":56,"createdAt":"2023-11-08 08:40:19.938542","bumpedAt":"2023-11-15 08:18:37.526242","views":337,"postsCount":5,"highestPostNumber":5,"likeCount":0,"closed":true,"pinned":false,"pinnedGlobally":false,"pinnedAt":null,"pinnedUntil":null,"isBanner":false,"excerpt":"实验 2.5 中用 bvh 加速光线求交。发现对 Model 进行 translation 平移变化时渲染物体会偏移严重，scale 放大缩小时正常。如图 1，translation(0,0,0) 渲染正常；图 2，translation(0, -0.5, 0) 不正常，偏移到只剩一个角。 # bvh.cpp optional<Intersection> BVH::intersect(const Ray& ray,…","deletedAt":null,"isAnonymous":false,"category":{"id":56,"name":"计算机图形学","slug":"cg","color":"92278F"},"author":{"id":71,"username":"waliwaliwa","name":"瓦利瓦利哇","avatarUrl":"/uploads/image/c2/dc/c2dc48ac49603de775e03ed2ff93bd18dc9f999d24303baf1edd0c847c7f2435.avif"},"tags":[]},"posts":[{"id":16567,"postNumber":1,"raw":"实验 2.5 中用 bvh 加速光线求交。发现对 Model 进行 translation 平移变化时渲染物体会偏移严重，scale 放大缩小时正常。\n[grid mode=\"tile\"]\n![figure1|640x500](/uploads/image/77/38/773842125e74e6c0e1bc5993ec789b3a72e8a1447aff67ef3ef6a8d59548db0f.avif)\n![figure2|640x500](/uploads/image/64/65/6465095b5986432b3d1c8b30aa5f1dcde952d6be613700d3669ef19182f73649.avif)\n[/grid]\n\n如图 1，translation(0,0,0) 渲染正常；图 2，translation(0, -0.5, 0) 不正常，偏移到只剩一个角。\n```c \n# bvh.cpp\noptional BVH::intersect(const Ray& ray, [[maybe_unused]] const GL::Mesh& mesh,const Eigen::Matrix4f obj_model){\n // ....\n trans_ray.direction =\n (model_inv * Vector4f(ray.direction.x(), ray.direction.y(), ray.direction.z(), 1.0f))\n .head<3>();\n trans_ray.origin =\n (model_inv * Vector4f(ray.origin.x(), ray.origin.y(), ray.origin.z(), 1.0f)).head<3>();\n isect = ray_node_intersect(root, trans_ray);\n if (isect.has_value()) {\n // 对 isect 返回值的一些变化操作\n // .....\n }\n}\n```\n应该是 ray_node_intersect() 有问题但不知道哪里有问题😖。","cooked":"

实验 2.5 中用 bvh 加速光线求交。发现对 Model 进行 translation 平移变化时渲染物体会偏移严重，scale 放大缩小时正常。

$\"figure1\"$
\n $\"figure2\"$

如图 1，translation(0,0,0) 渲染正常；图 2，translation(0, -0.5, 0) 不正常，偏移到只剩一个角。

# bvh.cpp\noptional<Intersection> BVH::intersect(const Ray& ray, [[maybe_unused]] const GL::Mesh& mesh,const Eigen::Matrix4f obj_model){\n  // ....\n  trans_ray.direction =\n          (model_inv * Vector4f(ray.direction.x(), ray.direction.y(), ray.direction.z(), 1.0f))\n              .head<3>();\n  trans_ray.origin =\n          (model_inv * Vector4f(ray.origin.x(), ray.origin.y(), ray.origin.z(), 1.0f)).head<3>();\n  isect = ray_node_intersect(root, trans_ray);\n  if (isect.has_value()) {\n  // 对 isect 返回值的一些变化操作\n  // .....\n  }\n}\n

应该是 ray_node_intersect() 有问题但不知道哪里有问题😖。

\n","createdAt":"2023-11-08 08:40:20.050201","updatedAt":"2023-11-08 08:40:20.050201","replyToPostNumber":null,"replyCount":0,"likeCount":0,"wordCount":147,"liked":false,"bookmarked":false,"polls":[],"reactions":[],"wiki":false,"version":1,"publicVersion":1,"deletedAt":null,"isAnonymous":false,"user":{"id":71,"username":"waliwaliwa","name":"瓦利瓦利哇","avatarUrl":"/uploads/image/c2/dc/c2dc48ac49603de775e03ed2ff93bd18dc9f999d24303baf1edd0c847c7f2435.avif","admin":false,"moderator":false,"signatureRaw":null,"signatureCooked":null}},{"id":16569,"postNumber":2,"raw":"太奇怪了，我也是这样，不知道是哪里出问题了","cooked":"

太奇怪了，我也是这样，不知道是哪里出问题了

\n","createdAt":"2023-11-08 08:42:35.338609","updatedAt":"2023-11-08 10:09:41.262426","replyToPostNumber":null,"replyCount":0,"likeCount":0,"wordCount":21,"liked":false,"bookmarked":false,"polls":[],"reactions":[],"wiki":false,"version":2,"publicVersion":2,"deletedAt":null,"isAnonymous":false,"user":{"id":349,"username":"SonnyMushroom","name":null,"avatarUrl":"/uploads/image/14/9e/149eee59defe0da3b9dfcf205f06b5a4b9704dc8316e95e13224903a2f026356.avif","admin":false,"moderator":false,"signatureRaw":null,"signatureCooked":null}},{"id":16643,"postNumber":3,"raw":"在模型坐标系中求解得到结果后，返回的时候需要再乘以 model 得到返回值，这个结果像是有关模型坐标系的变换出现了一些问题","cooked":"

在模型坐标系中求解得到结果后，返回的时候需要再乘以 model 得到返回值，这个结果像是有关模型坐标系的变换出现了一些问题

\n","createdAt":"2023-11-09 06:58:16.002041","updatedAt":"2023-11-09 06:58:16.002041","replyToPostNumber":null,"replyCount":0,"likeCount":0,"wordCount":55,"liked":false,"bookmarked":false,"polls":[],"reactions":[],"wiki":false,"version":1,"publicVersion":1,"deletedAt":null,"isAnonymous":false,"user":{"id":1488,"username":"roland","name":"李昌洲","avatarUrl":null,"admin":false,"moderator":false,"signatureRaw":null,"signatureCooked":null}},{"id":17087,"postNumber":4,"raw":"上次的问题还没有解决😭。当设置 Model 偏移量很小的时候**translation(0,0.1,0)** 渲染出来存在黑色块。\n![byh_y+|636x500](/uploads/image/41/dd/41dd11996b0ddd1d4b794ea7cc6544c602f391387351f799fda9d3474c02c259.avif)\n```c\n// 使用 BVH 求交\noptional BVH::intersect(const Ray& ray, [[maybe_unused]] const GL::Mesh& mesh,\n const Eigen::Matrix4f obj_model)\n{\n model = obj_model;\n optional isect;\n if (!root) {\n isect = std::nullopt;\n return isect;\n }\n Ray trans_ray;\n Eigen::Matrix4f model_inv = this->model.inverse();\n trans_ray.direction =\n (model_inv * Vector4f(ray.direction.x(), ray.direction.y(), ray.direction.z(), 1.0f))\n .head<3>().normalized();\n trans_ray.origin =\n (model_inv * Vector4f(ray.origin.x(), ray.origin.y(), ray.origin.z(), 1.0f)).head<3>();\n isect = ray_node_intersect(root, trans_ray);\n if (isect.has_value()) {\n Vector3f world_intersection =\n (model * (isect->t * trans_ray.direction + trans_ray.origin).homogeneous()).head<3>();\n float dis = (world_intersection - ray.origin).norm();\n isect->t = dis;\n isect->normal = (model_inv.transpose() *\n Vector4f(isect->normal.x(), isect->normal.y(), isect->normal.z(), 1.0f))\n .head<3>();\n }\n return isect;\n}\n```\n是**if (isect.has_value())** 中对返回值的坐标变换存在问题吗，还是在 **ray_node_intersect()** 函数进行一些特殊处理？","cooked":"

上次的问题还没有解决😭。当设置 Model 偏移量很小的时候translation(0,0.1,0) 渲染出来存在黑色块。
\n $\"byh_y+\"$

// 使用 BVH 求交\noptional<Intersection> BVH::intersect(const Ray& ray, [[maybe_unused]] const GL::Mesh& mesh,\n                                      const Eigen::Matrix4f obj_model)\n{\n    model = obj_model;\n    optional<Intersection> isect;\n    if (!root) {\n        isect = std::nullopt;\n        return isect;\n    }\n    Ray trans_ray;\n    Eigen::Matrix4f model_inv = this->model.inverse();\n    trans_ray.direction =\n        (model_inv * Vector4f(ray.direction.x(), ray.direction.y(), ray.direction.z(), 1.0f))\n            .head<3>().normalized();\n    trans_ray.origin =\n        (model_inv * Vector4f(ray.origin.x(), ray.origin.y(), ray.origin.z(), 1.0f)).head<3>();\n    isect = ray_node_intersect(root, trans_ray);\n    if (isect.has_value()) {\n        Vector3f world_intersection =\n            (model * (isect->t * trans_ray.direction + trans_ray.origin).homogeneous()).head<3>();\n        float dis     = (world_intersection - ray.origin).norm();\n        isect->t      = dis;\n        isect->normal = (model_inv.transpose() *\n                         Vector4f(isect->normal.x(), isect->normal.y(), isect->normal.z(), 1.0f))\n                            .head<3>();\n    }\n    return isect;\n}\n

是if (isect.has_value()) 中对返回值的坐标变换存在问题吗，还是在 ray_node_intersect() 函数进行一些特殊处理？

\n","createdAt":"2023-11-14 09:13:30.433793","updatedAt":"2023-11-14 09:13:30.433793","replyToPostNumber":null,"replyCount":0,"likeCount":0,"wordCount":165,"liked":false,"bookmarked":false,"polls":[],"reactions":[],"wiki":false,"version":1,"publicVersion":1,"deletedAt":null,"isAnonymous":false,"user":{"id":71,"username":"waliwaliwa","name":"瓦利瓦利哇","avatarUrl":"/uploads/image/c2/dc/c2dc48ac49603de775e03ed2ff93bd18dc9f999d24303baf1edd0c847c7f2435.avif","admin":false,"moderator":false,"signatureRaw":null,"signatureCooked":null}},{"id":17149,"postNumber":5,"raw":"同学，注意到你的光线的方向向量和起点坐标在变为齐次坐标时，都是添加的 1。而事实上，坐标值确实应当添加 1，而向量则应当添加 0。","cooked":"

同学，注意到你的光线的方向向量和起点坐标在变为齐次坐标时，都是添加的 1。而事实上，坐标值确实应当添加 1，而向量则应当添加 0。

\n","createdAt":"2023-11-15 08:18:37.526242","updatedAt":"2023-11-15 09:21:22.111837","replyToPostNumber":null,"replyCount":0,"likeCount":0,"wordCount":59,"liked":false,"bookmarked":false,"polls":[],"reactions":[],"wiki":false,"version":1,"publicVersion":1,"deletedAt":null,"isAnonymous":false,"user":{"id":1488,"username":"roland","name":"李昌洲","avatarUrl":null,"admin":false,"moderator":false,"signatureRaw":null,"signatureCooked":null}}],"hasMore":false,"lastReadPostNumber":5,"hasUrlPostNumber":true}