A multi-scale VR navigation method for VR globes

Figures & data

Figure 1. Simultaneous navigation in a real space and a virtual space: (a) a user navigates in a real space; (b) a user navigates in a virtual space.

Figure 2. Multi-scale navigation in a virtual globe environment realized by altering the viewing distance.

Figure 3. A VR user interacts with a multi-scale virtual environment: (a) a VR user touches and rotates the globe with a hand controller; (b) a VR user freely walks through a city and collects buildings.

Figure 4. Collision between the VR viewpoint and virtual scenes: (a) the VR viewpoint goes into a wall because the obstruction of the wall is not considered; (b) the VR viewpoint is gradually covered by a mountain because the topographic relief is not considered.

Figure 5. (a) Scene plane and (b) navigation plane.

Figure 6. Relative location relationships between the scene and navigation planes: (a) aligned; (b) rotational.

Figure 7. Relative location relationships between the scene and navigation planes: (a) scaling; (b) offset.

Figure 8. The 2D map partition method in OGC Web Map Tile Service.

Figure 9. Octree structure-based globe space partitioning.

Table

Algorithm 1. Octree update algorithm
Input: Newly loaded drawing object(Object)
root of the subspace where the object is located(Root)
Step 1. Set the currently processed node: Node = Root
Step 2. If the spatial range of the Node intersects with the bounding box of the Object, insert the Object into the Node
Step 3. If the Node has children(Children):
For each Child in Children
Set Node = Child, Go To Step 2;
End For
Else if the total number of vertices in the Node exceeds the threshold value, go to Step 4
Step 4. If the total number of nodes of the octree is smaller than 50% of the total number of inserted drawing objects:
Generate sub-nodes of the Node by evenly dividing the longitude, latitude and height;
Distribute all drawing objects in the Node to the sub-nodes.

Table

Algorithm 2. Octree search algorithm
Input: Octree node where the VR viewpoint is located in the previous frame (Node0);
Smallest bounding sphere with the VR viewpoint as the center and the user’s height as the radius(Sphere)
Output: Octree node where the current VR viewpoint is located (Node0);
The set of found drawing objects(Objects)
Step 1. Set Node = Node0;
Step 2. If the Sphere is contained within the spatial range of Node, go to Step 3;
Else set Node to its parent node, and go to Step 2;
Step 3. If Node has children(Children):
For each Child in Children
If the spatial range of the Child does not intersect with Sphere, continue
If the Sphere is contained within the spatial range of the Child and the Child tree depth is greater than Node0:
Set Node0 = Child;
Set Node = Child;Go to Step 3;
End For
Else, insert all the drawing objects in Node into Objects (remove duplicate drawing objects)
Step 4. Terminate the algorithm and return Node0 and Objects

Figure 10. (a) When moving the navigation plane will cause a collision between the VR viewpoint and the scene, the request for movement is declined to prevent the VR viewpoint from going into the wall; (b) when moving the navigation plane will not cause a collision between the VR viewpoint and the scene, the request for movement is accepted and the navigation plane is lifted upward to enable its origin to adjoin the local scene to prevent the VR viewpoint from sinking into the ground.

Figure 11. (a) If the VR viewpoint goes into a wall, the navigation plane is horizontally offset. As a result, the VR viewpoint horizontally moves from VP1 to VP2. (b) If the VR viewpoint sinks into the ground, the navigation plane is vertically offset. As a result, the VR viewpoint vertically moves from VP1 to VP2.

Figure 12. Imagery observed from the VR viewpoint when the scaling ratio N is set to 5,000,000.

Figure 13. Imagery observed from the VR viewpoint when the scaling ratio N is set to 20,000.

Figure 14. Imagery observed from the VR viewpoint when the scaling ratio N is set to 100.

Figure 15. Imagery observed from the VR viewpoint when the scaling ratio N is set to 15.

Figure 16. Imagery observed from the VR viewpoint when the scaling ratio N is set to 1.

Figure 17. Indoor navigation performance.

Figure 18. Google Earth VR (a) global-scale image and (b) building-scale image.

Figure 19. Total drawing time and navigation time during the navigation process.

Figure 20. Total drawing time and navigation time with different scene complexities.

Figure 21. Comparison of the viewpoint correction time when different space-partitioning algorithms are employed.

Figure 22. Comparison of the update time of the two space-partitioning algorithms.