Using pole photography and SfM photogrammetry for the documentation of archaeological sites

Ralf Hesse, State Office for Cultural Heritage Baden-Württemberg, Germany

STATE OFFICE FOR CULTURAL HERITAGE

Using pole photography and SfM photogrammetry for the

documentation of archaeological sites

From the top of a pole - a vantage point between ground and air

• useful height range � area coverage and resolution• low cost, easy to use• previously:

• airplanes• ladders, cranes, cameras hanging from tilted poles

� (single) vertical photos• now:

• UAVs, kites, poles� (many) oblique photos � SfM � DSM, orthophoto

From the top of a pole - a vantage point between ground and air

• usefulness of height range

• between 3 and >10m

• between observer on the ground and low-flying aerial platforms

• 2 x height � 4 x area

• areas from a few m2 to c. 1 ha

• e.g. excavations, rock art, earthworks, remains of buildings

From the top of a pole - a vantage point between ground and air

• advantages

• low cost

• portability

• easy to use

• legal issues (as compared to UAVs)

• how high can we get?

• easy: 3-4 m

• ok: 4-6 m

• difficult: > 6-8 m

From the top of a pole - a vantage point between ground and air

• what pole for pole photography?

• material: metal, fibre glass or carbon fibre

• monopods, special pole photography poles (up to 10 m or more)

• window cleaning poles (up to 10 m)

• painting poles (up to 5 m)

• fishing rods (up to 13 m)

• radio antenna masts (up to 10 m)

• vehicle mounted masts (>10 m)

From the top of a pole - a vantage point between ground and air

• how to put the camera on the pole?

• tripod screw and ball head

• gorilla pod

• what camera to use?

• lightweight

• automatic interval shooting (or remote control)

• most Canon Powershot cameras (+CHDK)

• Pentax WG-1 (10 s intervals only)

• some Ricoh cameras

From the top of a pole - a vantage point between ground and air

• health and safety

• poles can bend, break or collapse, cameras can fall off

� loss of equipment and serious injuries

• don't use pole-mounted cameras over people

• always know where to drop the pole without hurting yourself or others

• don't use poles near power lines

• if possible, don't use poles under trees or in/near buildings

• make sure that camera is properly fixed to the pole

• make sure that the pole cannot collapse

• don't tilt the pole

• don't use a pole in strong or gusty wind or during thunderstorms

• if possible, use a lightweight camera

• wear protective clothing if necessary (work gloves, helmet)

From the top of a pole - a vantage point between ground and air

• covering an area (for SfM)

• referencing to a grid: place markers at known positions

• every point has to be visible in 3+ photographs taken from different positions

• make sure you don't photograph the shadow of the pole

• cover the area in equally spaced parallel stripes

• cover an area somewhat larger than the actual area of interest

• avoid corridor mapping (long single line of photos)

• make sure no points are obscured

• viewing angle should not change drastically between adjacent images

From the top of a pole - a vantage point between ground and air

• SfM processing (Agisoft Photoscan)

• mask shadow of pole etc.

• camera calibration “separate”

• visualising the DSM

• same visualisation techniques as for Lidar DEM

From the top of a pole - a vantage point between ground and air

• example 1: looting traces (Peru)

• area: 1400 m2

• resolution: 1 cm (1 mm)

• 745 photos taken in 70 min.

From the top of a pole - a vantage point between ground and air

• example 1: looting traces (Peru)

From the top of a pole - a vantage point between ground and air

• example 1: looting traces (Peru)

From the top of a pole - a vantage point between ground and air

• example 2: geoglyph damaged by Dakar rally (Peru)

• area: 3300 m2

• resolution: 1 cm (2 mm)

• 324 photos taken in 45 min.

From the top of a pole - a vantage point between ground and air

• example 2: geoglyph damaged by Dakar rally (Peru)

From the top of a pole - a vantage point between ground and air

• field work at Italica:

• Casa de Pajaros and other houses (1514 photographs)

• house plans

• mosaic floors

• domestic bath

• Amphitheatre (1244 photographs)