Panoche Gates 230kV Transmission Line LiDAR & Photogrammetry Survey — Pacific Gas & Electric

Tetra Tech completed a 43-mile LiDAR & photogrammetry survey of a 230kV transmission line in Central CA. The photogrammetry was utilized for planimetric mapping of features under the line including roads, canals, and buildings while feature extraction from the LiDAR data was used to create as-builts of the transmission line for a rerate study. Airborne GPS was employed to minimize the number of ground points that were needed to adequately control the photogrammetric mapping. Aerial acquisition consisted of 114 exposures flowin in 3 lines with ABGPS which allowed reduction of the set of ground surveyed control points to only fourteen; arranged in pairs to stabilized the aerotriangulation solution. The ABGPS data was reduced using six CORS stations whose distribution surrounded the project area. The LiDAR mission included 46 flight lines. Much of the project area could be covered by single passes of the instrument however multiple passes were necessary at the terminal sub-stations and wherever photo control points had been set to support the aerial photography. The adjacent and overlapping lines at the substations were made in opposing directions to facilitate instrument calibration. The LiDAR data was initially processed to classify the ground class. Points above the ground were grouped by their elevation as high, medium or low vegetation. Towers that constitute the line under study were reclassified as towers by inspection, moving along the alignment tower by tower. The wire class was generated linking the towers and the attachments to the towers were placed at the appropriate wire location. The design density of more than 20 points per square meter was sufficient that even small crossing wires were identifiable in the returns. All of the mapped features were written out to text files for introduction to PLS-CADD. The photogrammetric mapping was also introduced to PLS-CADD by the attachment of a DXF file generated from the mapping. Tetra Tech also provided photographs of each tower in an image catalog which is used by the PG&E electrical engineers while working in PLS-CADD. As with all projects, Tetra Tech provided a detailed technical report documenting accuracy, survey and AT methodologies and results, weather parameters during acquisition, metadata, and associated photos and graphics.


Peter Ashley

(925) 280-7441