Digital Cameras In Indonesia
Trials of a mid-format digital camera mounted on a helicopter have been conducted by a mining company in Indonesia. The trials were part of a project to map the vegetation around a site in Indonesia before the start of mining.
The survey co-ordinator in charge of the trial, Greg Little, said: 'The idea came about because we wanted to capture images of all areas of our two projects that would record the state of the environment before we moved into the areas.
'I approached a local helicopter charter company to see if they had any ideas for how we could safely capture images from their helicopter. I was looking at taking oblique photographs through the door. As it turns out their smallest helicopter (a Bell 206) had been used for a similar exercise a few years earlier. That exercise had used a film camera, so the helicopter already had a small hole cut in the rear left hand side floor (about 400mm x 250mm). Usually, this hole was bolted closed.
'The maintenance crew and I manufactured a bracket that was bolted onto the floor. My Canon EOS 300D bolted onto the bracket, pointing downwards. We then connected a remote switch to the camera and activated the switch on a manually timed basis.
'To determine the required time interval between photographs I produced a small table that estimated the time required at different speeds for different ground image sizes. As it turned out we needed to capture an image every five seconds. I have software which will allow me to automatically capture images on a timed basis through a notebook computer, but I was a little nervous about using this as I could not be sure how long the notebook battery would last.
'In one day we flew two of our project areas. Generally we flew at an altitude of 2500 feet. We took about 1200 images. We had survey control scattered around both projects to allow us to interpret 3D data at a later stage.
'We sent ten images to Adam Technology in Perth where staff generated a 3D model and a series of ortho rectified images using the company's 3DAnalyst product. We then compared those images with some ground survey.
'The images used in the trial were all captured with an aperture value of f8 and a shutter speed of 1/250 sec. The focus was set manually at the beginning of the day, along with the focal length, at 28 mm. The lens was a 28-135 mm zoom lens. The lens was then taped so the lens wouldn't wonder off focus or focal length.
'The survey control used in the images was scattered along the length of the pit. They were not ideally situated from a geometric point of view, but the software managed to handle it okay.'
After digitising the control points, the images were processed automatically by 3DM CalibCam to generate the relative-only points and derive the exterior orientations. 3DM Analyst was then used to generate the DTMs and export the data as orthorectified TIFFs. They were then imported into Trimble's Terramodel software.
During the block adjustment, three of the 15 control points were found to be in error (subsequently confirmed by the mine's survey advisor and disabled).
The camera used for this trial was Canon's cheapest digital single lens reflex camera, worth about US$700.
A spokesman for Adam Technology says the resulting imagery has a height accuracy of better than 100 mm, well within the requirements for the project.
(This page last modified on 12 April 2005)