HJW GeoSpatial, Inc.- Services- LiDAR Terrain Modeling

HJW GeoSpatial Services

LiDAR Processing and Terrain Modeling
LiDAR (Light Detection and Ranging) technology used to gather high density terrain data from an aerial platform. Laser pulses traveling at the speed of light are sent from a LiDAR scanner to the terrain, and reflect back to the sensor. The duration of time that the pulse travels is used to compute the distance to the terrain (the range), and airborne GPS/IMU data allows for the range data to be geo-referenced.

LiDAR data often contains multiple returns for each laser pulse, some on the surface of the ground, and other returns on vegetation or buildings. Many laser pulses never make it to the ground due to obstructions. In order to designate which points have actually hit the ground, the data must undergo filtering and classification after data acquisition.

Incorporating photogrammetry into the classification and QA/QC of LiDAR data greatly increases the degree of confidence in the final product.

Without the guidance of photogrammetric operations, LiDAR points themselves are not an ideal representation of the terrain. Automated filtering routinely misclassifies points as “bare earth”, when they are in fact on vegetation. Additionally, there should be methods in place to constrain the terrain model to represent characteristic features. These issues become apparent as when visually inspecting contour data generated directly from the “bare earth” LiDAR data. For these reasons, we recommend an approach that incorporates photogrammetric analysis and sometimes mapping and editing.

HJW’s approach to LiDAR processing sets itself aside from industry standards by emphasizing the use of photogrammetric methods for interpreting and classifying the point data. We use these methods to supplement automated classification procedures. This is in sharp contrast to the standard approach of interpretation, which uses point clouds and surface models only.

With orthophotos as a backdrop, areas with dense vegetation can be scrutinized and manually classified. Photogrammetric stereo-models can be used to verify that the points are on the ground and not “floating”. Also, photogrammetric stereo-models can be used to manually measure breaklines to supplement the LiDAR point cloud. Breaklines on representative features allow for more accurate contours and terrain models.

Our quality control procedures adhere to standards set forth by the American Society of Photogrammetry and Remote Sensing, Federal Emergency Management Agency, and the National Digital Elevation Program. Our experts can work with your organization to design a project or quality control procedures to match your budget and requirements.