Photogrammetric Mapping IDIQ – Region 3

Project Description

Wiser provided 1776 tiles (8000 x 14000 ft.) of orthophotography covering 15 counties – Cheatham, Davidson, Houston, Humphreys, Macon, Montgomery, Robertson, Rutherford, Smith, Stewart, Sumner, Trousdale, Williamson and Wilson County.

Wiser used ImageStation OrthoPro (OrthoPro) to create orthophotography with 12 inch ground pixel resolution from the digital imagery provided by TDOT.

All images were orthorectified using the provided DEMs to remove the effects of the uneven ground surface. Then the orthorectified images were created for mosaicking using ISPM source images that were specified during the project preparation phase. After this the images were tonal balanced and adjusted to ensure consistent quality between photos.

Wiser generated seamlines along which the images were mosaicked.  Wiser reviewed and modified the seamlines to avoid crossing features such as buildings.

After the images were mosaicked and cut into tiles, the tiles were inspected for quality and seamline errors such as shifts between images, smears along seamlines, errors in the DEM surface, unacceptable color variances between images and other conditions that would detract from the smooth transition between images. The orthophotography was also reviewed against provided vector data to ensure that it still met horizontal accuracy. Each tile was also reviewed for edgematching with adjacent tiles including those tiles in adjacent regions and those provided by TDOT and other contractors.

Once all corrections to imagery were completed and verified, Wiser merged the tiles for each delivered county into a single SID image. The individual tiles were delivered at 12 inch ground pixel resolution in TIFF/TFW format.  All data was delivered in Tennessee State Plane NAD 1983, U.S. Survey Feet, NAVD 1988 coordinates.


Lake Purdy Mapping

Project Description

Lake Purdy is a 990 acre reservoir on the southeastern side of Birmingham, AL and is owned by the Birmingham Water Works Board (BWWB). Wiser was engaged to provide a detailed and highly accurate topographic survey covering the lakeshore and surrounding 12,000 acres in order to study the impact of a change in the pool elevation for additional storage.

Due to the size of the area, accuracy requirements and heavy tree cover, helicopter mounted aerial LiDAR was utilized for data acquisition. Wiser post-processed and classified the resulting data including bare earth ground distinction. The point cloud was then QC analyzed versus field collected RTK GPS points around the entire perimeter of the project. The analysis showed an average error of 0.13’ which was well within the 0.5’ accuracy requirement for the project. The point cloud was then classified for model key points to produce a data set with the proper balance of accuracy to data density.

One foot interval contours and digital elevation and terrain models were developed from the point cloud data. The deliverables included several formats of this data including ESRI ArcGIS DEM and Shapefiles, MicroStation Geopak TIN and Autodesk Civil 3D TIN.