SPAR Conference in The Hague

Taking part in the SPAR Europe Conference in The Hague this week made me feel a little out of place among all those business executives with their suits and ties. The t-shirt and sweater fraction was very likely below 10%, quite similar to the percentage of women attending this conference. So, yes, it was quite technical and business-oriented. It was interesting nonetheless to see the newest examples of 3D acquisition and application techniques.

Of course, the presentations by the business representatives were quite often of the “our product is the best on the market” or at least of the “look what we can do!” type. The more inquisitive approach that you find at scientific conferences would have made it more interesting (for me at least).

Still, the conference drew together a quite diverse range of people. The main focus seemed to be on terrestrial laser scanning on one hand and on airborne structure-from-motion on the other hand. Especially in the field of 3D generation from multiple digital photographs, the differences in technological complexity (and hardware costs) could not have been greater: from using smartphones or 99 € digital cameras to 260-megapixel cameras with 5 spectral channels or multi-camera setups capable to acquire one or two gigapixels per second, from working with a few images to processing 2.8 Million images in one large process (Building Rome on a cloudless day), from consumer laptops running open-source software to dedicated multi-processor number-crunchers deployable in aircrafts or hangars.

Asked about the processing time to create a dense 3D model from a given set of a few thousand photographs, one speaker said, well, that would depend on how many hundred processor cores we throw at the task. How surprising is it that one of the presentations with the technically most advanced setup had not only “gigapixels” but also “soldiers” in it? So while 3D methods (in particular photogrammetry / Structure from Motion) are becoming increasingly available for scientists having to work on a low budget (for example many archaeologists) or non-profesionals, military applications are, as usual, quite far ahead.

Pole “Aerial” Photography (PAP)

A while ago, I was trying to think of a way to take low-level aerial photographs with the purpose of documenting and photogrammetrically analysing things such as archaeological sites and sand dunes. Renting an airplane was out of the question, and model airplanes, helicopters, quadrocopters or octocopters appeared to be technologically too complex (and costly). Finally, I came across Kite Aerial Photography (KAP) and Pole Aerial Photography (PAP).

To begin with, I am not sure why this is called Pole Aerial Photography. Nothing is airborne here. I am standing with my feet firmly planted onto the ground, holding the bottom end of a pole which has a camera at its top end. Of course, you get elevated views which do sometimes look as if they were taken from an airborne platform.

While spending quite some time trying to find out how to do things best, I got lots of inspiration from what PAP people wrote on their websites. The first thing you need for PAP, of course, is a pole. It should be lightweight, stable, easy to set up and easy to pack up for transport. People use all kinds of poles such as professional window cleaning equipment, 9 to 13 metres long carp fishing poles, GPS poles and the like. They are usually made of carbon fibre, fibreglass, steel or aluminium.

One of my requirements was to be mobile – both when travelling and when shooting pictures. Can you take a ten metre window cleaning pole (which is still more than two metres long when packed up) on a flight without having to pay extra? No. The solution was a collapsible ten metre fibreglass pole sold by DX-Wire as a ham radio antenna mast. Packed up, it is only 0.67 metres long, so I can just put it in my backpack. The top segments (above approximately seven metres) are too weak to carry a camera. As I was not aiming for great heights, I decided to use only the lower 5.7 metres, weighting less than 1 kg.

To attach the camera to the top of the pole, I used epoxy to glue a 1/4′ tripod screw into the top of the uppermost pole segment. To this I attach a small, light-weight tripod ballhead after expanding the pole. Attach the camera, adjust the viewing angle, ready. The camera (I am using a Canon G12 and a Canon A3000IS) runs CHDK with a simple intervalometre script that takes pictures at intervals of a few seconds.

Camera attached to tripod ballhead on top of the pole.

A useful addition is a bubble level which can easily be attached to the lower part of the pole to help keeping it vertical.