Orthophoto & Planimetric Data for CFB Halifax

Department of National Defence, Canada

Background
Canadian Forces Base Halifax required detailed, large scale imagery and planimetric data collection for 6 of their Halifax sites. The imagery was to form the backdrop for their GIS development and was to be used primarily for future development of CFB Halifax and to better manage assets and infrastructure owned and maintained by the base. The planimetric data formed the base inputs for the GIS data model. Eastcan was selected to provide aerial photography, orthophotos and planimetric data collection 6 sites in CFB Halifax. Eastcan contracted the aerial photography acquisition to JW Sewall, in Maine. Ground surveying was conducted by Eastcan’s parent company, Thompson Conn Ltd.

Project Workflow
The production included 4 primary stages:

Aerial Photography
The sites were flown with 1:3000 scale photos. Photography was flown in early May, 2010 and was controlled with ground based points (no airborne GPS). The project included 144 ground control points (targets and photo ID) on 200 air photos. The photography was scanned at 2000 dots-per-inch for a pixel dimension of 3.8 cm.

Data Compilation
Data collection included a detailed surface model and all visible, static assets for each site. Planimetric data was coded as per client specifications. Unknown features were classified during field inspections and ground truthing of the photogrammetric data collection. Data collection also included field work to locate assets not visible on the photography (too small or tree covered) and to verify accuracies and coding of the photogrammetric collection.

Ortho Creation
The imagery was re-sampled to 5 cm ground pixel size during the rectification process. The rectified images were mosaiced into tiles. The output mosaics were visually inspected for seam errors, smears and sun flares before final submission to the client.

GIS Structuring
Vector data was delivered in DWG and ESRI’s SHP format for incorporation into the client’s Geomedia data model. All data was topologically structured to meet the client’s specifications.