Fixing Nan errors in Camera Frustum Mesh (#1397)

* Issue was that when normalized, the look vector had a slight floating point imprecision that caused this to try and calculate a new up vector. Because the up vector was being rotated based on that floating point imprecision, it was trying to rotate around a (0,0,0) axis which caused nan values

* Adding a test with the look_at and position vectors very close to each other.

* Alternative to rounding the look vector values

src/libs/ascent/runtimes/flow_filters/ascent_runtime_rendering_filters.cpp

@@ -1922,8 +1922,8 @@ void generate_camera_meshes(conduit::Node &image_data){
   vtkm::Vec<vtkm::Float64,3> forward(0,0,-1);
   double angle_between = vtkm::ACos(vtkm::Dot(forward, vtkm_look)) / vtkm::Pi() * 180;
 
-  // If the look vector has been rotated by a certain angle, ajust the camera up vector to match
-  if (angle_between != 0.0) {
+  // If the look vector has been rotated by a certain angle, adjust the camera up vector to match
+  if (vtkm::Abs(angle_between) >= 0.001) {
     vtkm::Vec<vtkm::Float64,3> axisOfRotation = vtkm::Cross(vtkm_look, forward);
     vtkm_up = 
       vtkm::Transform3DVector(vtkm::Transform3DRotate(-angle_between, axisOfRotation), vtkm_up);

src/tests/ascent/t_ascent_render_3d.cpp

@@ -3004,7 +3004,7 @@ TEST(ascent_render_3d, test_render_3d_camera_frustum_meshes)
 
     EXPECT_TRUE(conduit::blueprint::mesh::verify(data,verify_info));
 
-    ASCENT_INFO("Testing 3D rendering of camera frustum meshes");
+    ASCENT_INFO("Testing 3D rendering of camera frustum meshes\n");
 
     //
     // Create the actions.
@@ -3048,6 +3048,13 @@ TEST(ascent_render_3d, test_render_3d_camera_frustum_meshes)
     add_plots["scenes/s1/renders/r4/camera/azimuth"] = 20.0;
     add_plots["scenes/s1/renders/r4/camera/elevation"] = -45.0;
 
+    // Test that if the look_at location and the position location are quite similar that the frustum 
+    // is still generated without errors.
+    add_plots["scenes/s1/renders/r5/image_prefix"] = 
+        conduit::utils::join_file_path(output_path, "tout_render_3d_frust_image_nan");
+    add_plots["scenes/s1/renders/r5/camera/position"] = {0.0, 0.0, 0.0581200011074543};
+    add_plots["scenes/s1/renders/r5/camera/look_at"] = {0.0, 0.0, 0.0};
+
     //
     // Run Ascent to generate images
     //
@@ -3065,7 +3072,7 @@ TEST(ascent_render_3d, test_render_3d_camera_frustum_meshes)
     //
     // For each image that was generated, run ascent to visualize the camera frustum
     //
-    for (int image_index = 0; image_index<4; image_index++) {
+    for (int image_index = 0; image_index<5; image_index++) {
         conduit::Node &image_node = ascent_info["images"][image_index];
         conduit::Node camera_data = image_node["camera/camera_frustum_mesh"];