The series relates to the functions of survey and mapping for Commonwealth Government purposes and Earth Sciences. The recording agency was responsible for the systematic geological and geophysical mapping of Australia for mineral exploration and other purposes. A894 consists of black and white positive photographic prints. Each item shows some or all of the following data: location, sortie or run number, negative number, scale, date, flight time, altitude, frame number. Frame and negative numbers are not necessarily the same.

From 1961 the agency employed civilian contractors to undertake aerial survey flights. The exception was when another government agency was known to be undertaking aerial survey work and arrangements were made to acquire copies of the negatives. Survey flights by civilian contractors were controlled by location, then run number, then negative. Some items in the series are controlled by a sortie number, then negative number. Sortie is a military term used, in this instance, to refer to the flying of a military aircraft on a mission.

Projects covered include civil and military projects in the ACT (including Jervis Bay). Locations include: the ACT city area, the Australian National University (ANU), Belconnen, Commonwealth Avenue, East Lake, Freshford, Ginninderra, Lanyon, Oaks Estate, Parliamentary Triangle, Tuggeranong town centre, Village Creek, and Wanniassa. Aerial survey negatives were processed to supply: a positive, for preparatory checking and scanning; and, a diapositive (positive transparency) used for the purpose of photogrammetric restitution.

Photogrammetry is a remote sensing technology that enables two dimensional images of three dimensional objects to be used to reconstruct accurate models of the original three dimensional scenes. Two or more images are taken from adjacent positions. Measurements are made in the images and common points identified in each image. Lines of sight (or rays) can then be plotted using the location the images were taken from and the identified points on the images. Triangulating the rays reconstructs the three-dimensional location of the identified points. The photogrammetric restitution process was a plotting instrument that, when set, reproduced maps and profiles from the diapositives, creating an optical stereoscopic model of the photographed terrain. These stereoscopic models were used to create accurate maps and survey plans and multiple printed copies could be produced from one original.

Sources

Series documentation

1 2 3 Photogrammetry.com, ‘What is Photogrammetry?’, downloaded 5 May 2009 from http://www.123photogrammetry.com/photogrammetry.html

Geoscience Australia website, downloaded 5 May 2009, http://www.ga.gov.au/about-us/history.jsp

Wikipedia.org, ‘Photogrammetry’, downloaded 5 May 2009 from http://en.wikipedia.org/wiki/Photogrammetry