on this page: steps | example | performance LOD | ranges | modes | selecting | adding a level | removing a level
A Level of Detail (LOD) grouping contains any number of child objects, referred to as levels. For a Distance LOD, you specify the distance at which each level is displayed. For a Performance LOD, you allow the browser to determine which level to display for optimal performance.
Find it: Click the Level of Detail Editor button on the Action
palette:
Follow these steps to create a simple LOD grouping:
Now that you have a basic feel for how an LOD grouping works, open the file /usr/share/Insight/library/SGI_bookshelves/Help/books/CosmoWorlds_UG/Models/brazier.wrl.
This LOD has a textured brazier for the first level, a brown cube for the second level, and an empty third level, as shown below. Its structure is typical of a useful LOD grouping, which usually contains a least one detailed object for close viewing, one stripped-down version, and one empty group for very far distances. You could also create another intermediate-level version of the first object using the Polygon Reduction Editor.
Select the object and open the Level of Detail Editor to examine the settings. Here's what you'll see:
Click the Performance box to convert an LOD to a Performance LOD, which allows the browser to select the appropriate level based on rendering performance, not distance. When you choose the Performance LOD option, the range bar shows "Best" at the left and "Fastest" at the right. The browser selects the level with the lowest index that it can render while still maintaining an acceptable frame rate. Some browsers may ignore this option.
When you've selected the Performance option, the Distances Computed from Point and Range Limit text boxes are grayed out.
For Distance LODs, distances are measured from the user's viewpoint to the center point of the object. You specify this center point by typing values into the x, y, and z text boxes shown under the label Distances Computed from Point in the Level of Detail Editor. The default center point is the origin (0 0 0). The brazier example shown earlier has a center of (740 127.007 -1187.5).
The Range Limit text field shows the range limit for any range but the last one. It reflects the limit of the currently selected range (in blue on the range bar). When you type a new value into this field and press Enter, the new value is shown on the range bar.
The LOD Editor has two modes, one for testing LOD groupings (Active LOD) and one for editing the levels (Keep Current Level). Use the Active LOD mode when you want to test the transitions between one level and the next. As you zoom in and out of the scene, the transition between levels should feel gradual; you don't want to see a sudden "pop" as levels switch. Use the Keep Current Level option to stay with one level so that you can perform detailed editing on it.
You can click and drag the range bar tick marks in either mode.
If the LOD grouping is selected, switching between levels doesn't change the current selection. If a level or part of a level is selected, switching between levels does change the current selection.
When you save the file, the Active LOD mode should be active. Note, though, that if you save, then select the LOD grouping, and then select an individual level, the mode switches automatically to Keep Current Level. This change enables you to make changes to the selected level. When you deselect the level and then select the entire LOD grouping, the mode returns to Active LOD.
Adding a level to an LOD grouping is the same as adding a child to any group. See Selecting and Grouping Objects for details.
Removing a level from an LOD grouping is the same as removing a child from any group. Select the level and then cut it or detach it from the group.