New Lidar Now Available for the Central Texas Region

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Additional newly acquired high resolution lidar data collected by Merrick & Company is now available and covers portions of Blanco, Caldwell, DeWitt, Gonzales, Kendall and Kerr Counties in central Texas. Aerial collection took place from January to March 2011 during the leaf-off season. URS provided third-party quality assurance and quality control (QA/QC). The data were funded by the Floodplain Mapping Group in tandem with the Strategic Mapping Program (StratMap) and were procured through the Council on Competitive Government’s High Priority Imagery and Datasets (HPIDS) contract.

This area of interest was selected based on statewide prioritization of floodplain mapping needs and coordination with the Federal Emergency Management Agency (FEMA). The project data were collected primarily for flood analysis to assist in floodplain management and mapping activities in Texas, however, the specification exceeds FEMA standards, allowing for a wide range of study.

Products

• Classified all-return lidar DO3Q tiles (1/16th of USGS Quad) in LAS 1.2 format
• Ground point Digital Elevation Model (DEM) in IMG (ERDAS Imagine) format
• Lidar intensity images in TIF format
• Hydro-flattening breaklines in SHP
• File-level FGDC metadata in XML

Acquisition Areas

802 tiles covering the majority of Gonzales, Kendall and Kerr Counties, large portions of Blanco and Caldwell Counties not already covered from a 2008/2009 CAPCOG collection, and partial coverage of DeWitt, Bandera and Gillespie Counties.

Product Specification

• Vertical accuracy (RMSE) tested at ~ 6 cm (2.4 in), exceeding the 15 cm state standard for Flood/Soils
• Average point density is ~ 6 points per square meter (ppsm), exceeding the 4 ppsm state standard
• Average ground spacing distance (GSD) is ~ 0.4 m (15.7 in)
• Point data are classified according to the following American Society for Photogrammetry and Remote Sensing (ASPRS) class schema:
  Class 1: Unclassified
  Class 2: Ground
  Class 4: Vegetation
  Class 6: Buildings
  Class 7. Low Point (noise)
  Class 9. Water
  Class 13. Bridges and Culverts
• DEM and Intensity Images are 1-meter spatial resolution
• Horizontal projection is UTM NAD83 Zone 14
• Vertical projection is NAVD88 Geoid 09
• Units are in meters denoting orthometric heights
• File structure is 1/16th of USGS 7.5 minute quadrangle (1.875 minute by 1.875 minute)

• Approximate file size per tile:
  Lidar (LAS) ~ 1.4 GB
  DEM (IMG) ~ 47 MB
  Intensity (TIF) ~ 10 MB

Order Data
Lidar data and the associated geospatial products listed above are available for cost of reproduction through TNRIS.