Updating Legacy Lidar Projects at USDA: Benefits, Challenges and Lessons Learned
The National Geospatial Center of Excellence (NGCE) provides the Natural Resources Conservation Service (NRCS) of the U.S. Department of Agriculture (USDA) with technical leadership in the geosciences. NRCS has a national strategy to acquire, integrate, and deliver high-quality elevation data that meets the Agency’s geospatial requirements. As part of this effort, NCGE maintains a national elevation dataset composed of laser imaging, detection and ranging (lidar) data acquired by government agencies. The NGCE lidar data archive is a collection of historical airborne lidar mapping projects dating back to 2001. It includes the legacy CLICK LIDAR data archive previously compiled by the U.S. Geological Survey (USGS).
NCGE has identified technical issues with older legacy lidar datasets that need to be addressed before they are published. Many of these datasets are in older versions of the LAS format and need to be updated to the current LAS V1.4 standard required by the USGS guidelines. This includes addressing the discontinued practice of using classes, rather than flags, to designate overlap points and model key points. Additional update issues identified include missing or incorrect coordinate reference system information, corrupt source files and the use of obscure point class schemas that do not correspond to current best practices. Starting in late 2015, NCGE began working with GeoCue Group’s Production Services Team to design and implement an update strategy for its lidar project archive with the goal to eventual publish all lidar datasets in its holdings for use by USDA stakeholders.
Updating the lidar project back catalog is beneficial for several NRCS end-user applications. Historically, NRCS applications have focused on developing bare earth digital terrain models for conservation planning and conservation practices. Recently there is interest in using the “value add” of vegetation and building classes to facilitate the extraction of canopy heights and buildings in the agriculture setting, to support agribusiness. NRCS is working with GeoCue’s production team to “value add” the existing data when updating the projects and to create workflows for generating elevation products and services to facilitate the planning of conservation practices where appropriate.
In this paper, we will review the issues identified when working with legacy lidar data sets, discuss the lidar dataset update workflow designed for NGCE and implemented by GeoCue Group, the expected and unexpected technical challenges encountered and the lessons learned to date. We will also discuss the potential to increase the value of these datasets for USDA applications such as conservation planning by implementing updated classification tables to include steps such as implementing a simple height above ground filter or adding model key points to a dataset that does not have them. Given the growing number of lidar projects being collected, the need for a comprehensive strategy to update and revise legacy datasets and back catalogs of project data will only increase, so lessons learned from this program will be relevant to numerous organizations.