[Figure 19] This hillside scan shows how reference balls can help the modeler and the person who is scanning the hillside. Image courtesy of Alan Lasky.

The person using the data, however, needs to pay careful attention to criteria associated with the acquisition of lidar data. Before approving any data that is received from a lidar capture session, the modeler responsible for using the data should make sure that the data meets the following criteria:

1. With each 3D data set should be an object in the scene of a known size. For example, if the modeler is receiving data that describes a large mountain, it would be impossible to determine the size of this mountain unless there was an object in the scene, such as a box that was five feet in all dimensions, to give scale to the entire scene. Without an object in the scene that determines the scale, a lot of guessing is involved when trying to use this data. Figure 19 shows a lidar scan of a hillside with small green balls placed in strategic areas toward the top of the hill. These balls are a specific size, so the modeler knows how large the scene is, and the balls are also used to line up additional scans of the same scene.

2. The data that is received should be placed relative to a true horizontal plane. Although the Cartesian coordinate system cannot be exactly duplicated in the real world, there should be some attempt to ensure that the data at least rests in a horizontal position.

Whenever possible, the objects that are seen in the background plate should also be visible in the scanned environment. This includes any props, buildings, and other stationary objects that can be seen in the background images. Figures 20 and 21 show how recognizable objects in a scene can help verify a database for scale, position and accuracy. Objects that are obscure shapes, such as rocks and plants, present a greater challenge when checking for scale, position and accuracy.

3. If possible, the lidar data should also include 3D data of the camera that was used to shoot the background plates. This can be useful in determining the actual distance between the camera and some of the identifiable objects in the scene.

4. The data received should be clean. Many times, the lidar data set that is received by the modeler comprises many individual snapshots of data that are taken at the sight of principal photography. When these individual small data sets are assembled into one large data set, many opportunities arise for holes and reversed faces to be introduced into the final data. Upon first viewing the data, the modeler should make sure all the faces are single sided and view the data carefully, inspecting it for holes and reversed faces.

[Figures 20 & 21] When objects that tie the scanned scene are easy to identify and recognize, the scene is easier to check for accuracy. Images courtesy of Alan Lasky.