The line width of a LineSet object cannot be modified.

[LMX-BY]

Checklist

• I have searched for similar issues.
• For Python issues, I have tested with the latest development wheel.
• I have checked the release documentation and the latest documentation (for main branch).

Proposed new feature or change

For the PointCloud type, you can modify the point_size in render_option to change the size of the points displayed. However, for o3d.geometry.LineSet, it seems that modifying the line_width in render_option does not change the width of the lines displayed. Is that correct?

References

No response

Additional information

No response

[cwreynolds]

Hi. I am not a maintainer, but this issue seems to have been around for a long time. This search finds reports going back to 2018: https://github.com/isl-org/Open3D/issues?q=is%3Aissue%20line_width

It was one of the first things I ran into when I started using a tiny subset of Open3D. (My report from 2023 is in that search above.) I ended up working around the issue using existing support for cylinders to construct lines with adjustable thickness, then transforming them to be placed between two endpoints. This is an expensive way to draw lines but seemed to work OK for my application.

    // An "Open3D native style" constructO3dCylinder from two endpoints
    static sp_tri_mesh_t constructO3dCylinder(double radius,
                                              const Eigen::Vector3d& endpoint0,
                                              const Eigen::Vector3d& endpoint1,
                                              int resolution = 20,
                                              int split = 4,
                                              bool create_uv_map = false)
    {
        // Get cylinder height and ensure it is not zero.
        double height = (endpoint1 - endpoint0).norm();
        assert(height > 0);
        Eigen::Vector3d axis = (endpoint1 - endpoint0) / height;

        // Use Open3D utility to create tri mesh with given radius, height, etc.
        using namespace open3d::geometry;
        auto cylinder = TriangleMesh::CreateCylinder(radius, height, resolution,
                                                     split, create_uv_map);
        
        // That cylinder is centered on Z axis. Move one endpoint to origin.
        cylinder->Translate({0, 0, -height / 2});
        
        // Pick an "up" vector which is "least parallel" to cylinder axis
        Eigen::Vector3d a(0, 1, 0);
        Eigen::Vector3d b(1, 0, 0);
        auto up = (std::abs(axis.dot(a)) < std::abs(axis.dot(b))) ? a : b;

        // Transform with origin at one cylinder ep, aligned with cylinder axis.
        using namespace open3d::visualization::gl_util;
        Eigen::Matrix4d lookat = LookAt(endpoint0, endpoint1, up).cast<double>();
        Eigen::Matrix4d cylinder_lookat_matrix = lookat.inverse();

        // Transform cylinder by LookAt transform.
        cylinder->Transform(cylinder_lookat_matrix);
        return cylinder;
    }

This is even further afield, but this is the code I used to test that function:

    // TODO 20241109 2-point cylinder demo
    static void cylinders_on_tri_mesh_edges()
    {
        auto vis = open3d::visualization::VisualizerWithKeyCallback();
        vis.CreateVisualizerWindow("TriangleMesh edges", 2000, 2000, 0, 0);
        
        double radius = 0.07;
        auto tri_mesh = open3d::geometry::TriangleMesh::CreateIcosahedron();
        std::set<std::pair<int, int>> edges;
        for (auto triangle : tri_mesh->triangles_)
        {
            for (int i = 0; i < 3; i++)
            {
                int a = triangle[i];
                int b = triangle[(i + 1) % 3];
                edges.insert(std::pair(std::min(a, b), std::max(a, b)));
            }
        }
        auto view = [&](const std::shared_ptr<open3d::geometry::TriangleMesh>& m)
        {
            m->ComputeVertexNormals();
            m->PaintUniformColor({0.75, 0.37, 0});
            vis.AddGeometry(m);
        };
        for (auto edge : edges)
        {
            auto v1 = tri_mesh->vertices_[edge.first];
            auto v2 = tri_mesh->vertices_[edge.second];
            auto cyl = constructO3dCylinder(radius, v1, v2, 100);
            view(cyl);
        }
        for (auto vertex : tri_mesh->vertices_)
        {
            auto s = open3d::geometry::TriangleMesh::CreateSphere(radius, 100);
            s->Translate(vertex);
            view(s);
        }
        vis.Run();
    }

That draws this:

[LMX-BY]

Hi. I am not a maintainer, but this issue seems to have been around for a long time. This search finds reports going back to 2018: https://github.com/isl-org/Open3D/issues?q=is%3Aissue%20line_width

It was one of the first things I ran into when I started using a tiny subset of Open3D. (My report from 2023 is in that search above.) I ended up working around the issue using existing support for cylinders to construct lines with adjustable thickness, then transforming them to be placed between two endpoints. This is an expensive way to draw lines but seemed to work OK for my application.

    // An "Open3D native style" constructO3dCylinder from two endpoints
    static sp_tri_mesh_t constructO3dCylinder(double radius,
                                              const Eigen::Vector3d& endpoint0,
                                              const Eigen::Vector3d& endpoint1,
                                              int resolution = 20,
                                              int split = 4,
                                              bool create_uv_map = false)
    {
        // Get cylinder height and ensure it is not zero.
        double height = (endpoint1 - endpoint0).norm();
        assert(height > 0);
        Eigen::Vector3d axis = (endpoint1 - endpoint0) / height;

        // Use Open3D utility to create tri mesh with given radius, height, etc.
        using namespace open3d::geometry;
        auto cylinder = TriangleMesh::CreateCylinder(radius, height, resolution,
                                                     split, create_uv_map);
        
        // That cylinder is centered on Z axis. Move one endpoint to origin.
        cylinder->Translate({0, 0, -height / 2});
        
        // Pick an "up" vector which is "least parallel" to cylinder axis
        Eigen::Vector3d a(0, 1, 0);
        Eigen::Vector3d b(1, 0, 0);
        auto up = (std::abs(axis.dot(a)) < std::abs(axis.dot(b))) ? a : b;

        // Transform with origin at one cylinder ep, aligned with cylinder axis.
        using namespace open3d::visualization::gl_util;
        Eigen::Matrix4d lookat = LookAt(endpoint0, endpoint1, up).cast<double>();
        Eigen::Matrix4d cylinder_lookat_matrix = lookat.inverse();

        // Transform cylinder by LookAt transform.
        cylinder->Transform(cylinder_lookat_matrix);
        return cylinder;
    }

This is even further afield, but this is the code I used to test that function:

    // TODO 20241109 2-point cylinder demo
    static void cylinders_on_tri_mesh_edges()
    {
        auto vis = open3d::visualization::VisualizerWithKeyCallback();
        vis.CreateVisualizerWindow("TriangleMesh edges", 2000, 2000, 0, 0);
        
        double radius = 0.07;
        auto tri_mesh = open3d::geometry::TriangleMesh::CreateIcosahedron();
        std::set<std::pair<int, int>> edges;
        for (auto triangle : tri_mesh->triangles_)
        {
            for (int i = 0; i < 3; i++)
            {
                int a = triangle[i];
                int b = triangle[(i + 1) % 3];
                edges.insert(std::pair(std::min(a, b), std::max(a, b)));
            }
        }
        auto view = [&](const std::shared_ptr<open3d::geometry::TriangleMesh>& m)
        {
            m->ComputeVertexNormals();
            m->PaintUniformColor({0.75, 0.37, 0});
            vis.AddGeometry(m);
        };
        for (auto edge : edges)
        {
            auto v1 = tri_mesh->vertices_[edge.first];
            auto v2 = tri_mesh->vertices_[edge.second];
            auto cyl = constructO3dCylinder(radius, v1, v2, 100);
            view(cyl);
        }
        for (auto vertex : tri_mesh->vertices_)
        {
            auto s = open3d::geometry::TriangleMesh::CreateSphere(radius, 100);
            s->Translate(vertex);
            view(s);
        }
        vis.Run();
    }

That draws this:

Thanks, this approach can solve the problem to some extent.