Aerial photography All (most) of our base data map layers have come from air photos http://lrdw.ca … imap

Traditional surveying: triangulation Theodolite Triangulation station Geodetic station

Early days: Boston, from Tethered Balloon (1860) Development of aerial photography before airplanes  

Air photos for reconnaisance from fighter planes and pigeons Word War I: Air photos for reconnaisance from fighter planes and pigeons Balloons and kites were easy to shoot down, but pigeons were not. Small cameras were attached to the birds and a timer was set to take pictures every 30 seconds as it flew

Oblique photos from mountain peaks

Early topographic mapping from mountain peaks: Canadian Rockies, 1890 Photo-topography led by Edouard Deville, was used until 1950 Early topographic mapping from mountain peaks: Canadian Rockies, 1890

Since 1945, all our topographic mapping is done from aerial photography: Air photos enabled a huge reduction in fieldwork costs, and an increase in how quickly and accurately large areas could be mapped Athabasca Glacier, 1958

Photos are not ‘planimetric’: there are distortions “Tip, tilt and swing” Relief distortion Radial distortion

There are two distinct branches of aerial photography: Photogrammetry:       "the science of obtaining reliable measurements from photos" Photo interpretation: "the identification and extraction of meaning of objects" Photogrammetry needs a minimum of 5 known point locations per photo

Accessing air photos

Index maps 1936-1950 microfiche, >1950 paper

Flight Reports organized by year

Flight map 1970_B-006-FI-70_16000

Photo library – Victoria, BC

Individual photos

Stereoscopes – 3D imagery

Stereo – 3D to create elevations

ORTHOPHOTOS Once corrected, and georeferenced, photos can be used for topographic mapping and as a mapping layer, with  map data overlain on top. A photograph that has been corrected and is 'planimetrically correct' is known as an  orthophoto (e.g. as in google maps, pgmap or BC- imap ).

Map layer features are identified using: Image interpretation http://airphotos.nrcan.gc.ca/photos101/photos101_info_e.php Map layer features are identified using: Shape Pattern Size Tone Colour Shadow Texture Site Time

Provincial photography is generally redone about every 10+ years City photography more frequently: 3-5 years PG 2003 2006 2010

Time sequence, PGmap: http://pgmap.princegeorge.ca/pgmap.html Aerial photos still use film, but these are then scanned and input into digital photogrammetric software for processing. Photos can be purchased as scanned TIF files

Digital photography: Terrasaurus aerial photography, Williams Lake http://www.terrasaurus.ca/