A LAS dataset pyramid structure is used to improve 3D display performance for a LAS dataset in ArcGIS Pro. It does this by organizing and indexing the points in a way that optimizes 3D display queries. LAS dataset pyramids use an octree-based indexing scheme that partitions space into a set of nested cubes. It's a 3D scheme that tends to retain more detail while still being fast. For example, an octree-based solution better supports visualizing and navigating to outlying points of a LAS dataset. The current status for the LAS dataset pyramid is reported on the LAS dataset properties dialog box. LAS dataset pyramid structure is created using the Build LAS Dataset Pyramid tool. LAS dataset layers that don't have a defined pyramid structure will behave as previously.
When a pyramid is built a folder of files is created in the same folder where the LAS dataset is stored. The naming convention for the pyramid folder is the .lasd name plus the suffix ..slas. A LAS dataset pyramid works only on a LAS dataset and not individual LAS or zLAS files. When a pyramid is made for a dataset it's version number is increased and can't be opened or used by older software (earlier than ArcGIS Pro 2.6). This can be remedied by making a version of the dataset without a pyramid; *.lasd files are small and easy to make. Alternately, you can revert as LAS dataset back to it's earlier version by using the LAS dataset properties dialog to delete the pyramid.
Pyramid selection methods
The LAS dataset pyramid partitions space into cubes, small cubes for more foreground rendering and large cubes for background rendering. Each cube references a point, which is a level-of-detail biasing that controls the influence of the visual experience in a 3D space. Pyramid bias types or selection methods allow control over how lower level-of-detail points get selected and displayed.
The point budget is not based on the assumption that all points will be displayed, but more intelligently on the filtered point counts. For example, if points are selected by the transmission line classification code, that classification code will get the whole budget and will be less likely to be thinned out of the rendering. Their display will be maximized in the scene.
There are four types of point selection methods in ArcGIS Pro for LAS dataset pyramids.
|Pyramid selection method||Description|
Closet to center
The point closest to the center of the cube is selected. This option is best when you don't have an application-specific interest in using the data. This method tends to produce renderings where the drawn point distribution is even.
The point selected is the weighted class code, with the class code selected given the highest weight. If you're focused on specific features, like powerlines, you can use this to make the points more apparent in the scene.
The lowest point in the cube is selected. This is a reasonable choice if your primary interest in the lidar is for water resources. For lower level-of-detail areas, it will tend to draw points in low areas and channels.
The highest point in the cube is selected. This is a good choice if your primary interest in the lidar is for any type of visibility, like obstructions or air navigation safety. It will bias rendering to the tops of buildings, antennae, tree tops, and so forth.
Create a LAS dataset pyramid
To create pyramids for a LAS dataset, follow these steps:
- Open the Build LAS Dataset Pyramid geoprocessing tool.
- Select the LAS dataset to generate pyramids for.
- Select the Point Selection Method to use for the pyramids.
- Click Run to execute the tool.
Update or edit a LAS dataset pyramid
When you manually edit the classification codes of a LAS dataset, they will automatically be reflected in the pyramid without making it out of date. The exception is if the pyramid is built with the class code weights selection method. In this case, the pyramid is still used for display but it's not guaranteed to honor the weighting scheme used to build the pyramid. Similarly, if you manually edit the withheld flag of one or more points the pyramid is still used for display but is technically considered out of date.
Use of any geoprocessing tool that edits class codes will make a pyramid out of date. The dataset will still display in this case, just without the benefit of the pyramid. If a pyramid is out of date run the Build LAS Dataset Pyramid tool to update the pyramid. The same tool is used to create a pyramid as to update a pyramid. You can tell if a pyramid is up to date by looking at its status on the Pyramid tab of the LAS dataset Properties dialog.
Adding and removing references to LAS files in an .lasd file makes the LAS dataset pyramids dirty, and it will need to be rebuilt. Use the Delete button on the LAS dataset properties dialog box to remove the pyramid structure and run the Build LAS Dataset Pyramid geoprocessing tool to rebuild it.
The pyramid building process will use memory as available then page to disk if needed. The paged data gets written to the geoprocessing scratch workspace. This location can be set on the geoprocessing environment tab. The amount of temporary disk needed is roughly the shortfall between available memory and the size of the input (uncompressed) LAS files. More memory availability will reduce the need for disk and will improve processing time. 16 GB of RAM is a recommended minimum. Processing of larger datasets will benefit from more memory.