Historical Air Photos contain valuable information, which for the most part remains untapped. Digitally scanned and properly ortho mosaicked historical air photos can bring this information to life, making it possible to analyze/visualize the historical information using modern GIS systems. These historical images can reveal hidden patterns, provide a deeper understanding of changes over time thus leading to better decision making.
PCI Geomatics announced the completion of a project to process historical airphotos for the GIS department of Fairfax County, VA. In 2017, the county GIS team contacted PCI Geomatics to help correct its remaining historical airphotos from 1960 and 1976. The 1976 imagery was particularly unique as it was the first color imagery collected of the entire county. The experts at PCI Geomatics used its Geomatica Historical Airphoto Processing (HAP) software to produce accurate, complete, high-quality ortho mosaics of the data.
The county had recognized the long-term value of historical imagery and invested in preserving the information contained in older images through systematic scanning and ortho mosaicking. The county GIS team also created Historical Image Viewer, an innovative and easy-to-use app, available through its web portal, to showcase historical ortho mosaics.
"The deterioration of historical airphotos and the gradual disappearance of aging film rolls that contain the original photos was a key motivation towards the preservation efforts required to keep these invaluable historical and archival records," said Tom Conry, GIS Manager at Fairfax County. "While scanning the data to create and update archival digital records was an essential first step, creating seamless ortho images made them readily accessible by our web users. We have added the 1960 and 1976 imagery to the existing 12 years of historic imagery in Historical Image Viewer."
"Now that the data has been corrected and made available to the public, we have seen an increase in the popularity of this application on our web portal."Conry added. "The imagery can be used for many applications, most notably change detection."
Many organizations today face challenges and high costs with storing analog data, and that such data; namely, contact prints and film, continues to degrade as time goes on. To address these challenges, PCI Geomatics developed HAP, a viable, cost-effective solution for organizations to preserve and use their airphoto archives in today's increasingly digital world.
HAP uses a multipass process and automatically collects ground control points and tie points to first accurately align the airphotos, which is particularly important with older data. Typically, older airphoto projects flew with stereo overlap, from which elevation products, such as digital surface models and digital terrain models, were created. After initial processing, the imagery is then orthorectified and color balanced to create the ortho mosaics.