Notes on Kite Aerial Photography: Background

KAP Technique
On Positioning the Camera


In April 1997 Simon Harbord framed one of the critical KAP questions in this site's KAP Discussion page. When I began taking kite aerial photographs two years ago I assumed that the ability to compose images in absentia was simply a matter of practice. One would imagine the scene from the point-of-view of the camera, adjust for the camera's lens, and adjust as necessary. The KAPer must have a good sense of where the KAP rig is in an absolute sense -- is it above or below the target, to the left or right, in front of or beyond? You must also have a sense of the camera's relative orientation - is it point to the horizon or downward, and toward what portion of the compass? I find that I am pretty accurate with four of these position variables but disturbingly inept in the fifth: establishing the KAP rig’s position downwind.

The description below is somewhat skewed by my practice of controlling the camera from the location where the kiteline is anchored -- often while handholding the kiteline reel.  This practice gives me feedback regarding the kite's "state of mind" and thus a sense of control over the kite.  I can react to changes in its flying behavior. Here is how I manage the five major position/orientation control variables:

1. Changing the position of the airborne rig to the left or right is accomplished by moving the anchor point of the kite (the kiteflyer walks to the left or right). Assuming there is room to maneuver – and KAPers are constantly assessing this – it is easy to position the rig along this axis. It is also straightforward to interpret the rig's position by sighting down the line.

2. The KAP Rig's position in terms of distance away from the kiteflyer is adjusted by moving the kite anchor point or by adjusting the amount of kiteline that is played out. It is notoriously difficult to gauge how far downrange the camera rig is actually flying. This is in part due to the sky’s lack of depth-related clues. I find this variable the most difficult to gauge in positioning the KAP rig. Comments on my technique are included in the next section of this page.

3. The height of the KAP Rig above the ground is controlled  by amount of line played out, the kite's flying characteristics, and the amount of wind. I’ve found it moderately easy to gauge this dimension of camera position through experience.

4. The azimuth (compass) orientation of the camera is usually gauged by looking at the rig. This variable is controlled by radio input (or presetting a manual rig). Many rigs feature telltale sticks projecting from the camera rig, often carrying the antenna away from the photo. If the camera rig is close then it is easy to see its compass orientation.  When the rig is distant there is more of a problem.  I sometimes rely on the position of the radio control lever and sometimes I use binoculars to see the telltale stick.

5. The altitude (tilt) orientation of the camera is also set by radio input. For this variable I find myself trusting the position of the stick on the radio transmitter. The rig is adjusted so that on end of the stick’s travel points the camera toward the horizon while the other points the camera toward the nadir. This variable is easy to master.

So it seems, as Simon pointed out, it is the camera rig’s position down range that is the most difficult to control accurately. Submit your favorite techniques to this discussion group and I will gather them later to append to this page.


An approach based on measurement and calculation

I’m currently working on a technique that uses a fascinating infrared pulse laser rangefinder, an optical clinometer, and a slide rule to compute down range position. I will report more as I learn it. In the meantime here are images of the instruments:

bushnell.gif (40245 bytes)The Bushnell Yardmaster 400 Laser Rangefinder bounces eye-safe infrared laser pulses off   a target and times the reflection of this energy back to the device.  The technique yields accuracy to plus or minus one meter.  The device is lightweight and simple to use.  I find it can range the camera cradle out to around 250 meters.   I believe I can extend this by adding reflective tape to the camera rig.  It can range the kite up to around 350 meters.  This is really a handy device.


suunto.gif (40473 bytes)A Suunto clinometer allows quick optical sights of the altitude of objects (e.g.; kite, camera cradle) in degrees above the horizon.




slide rule.GIF (40636 bytes)The Pickett 5" pocket slide rule provides a handy set of trig scales.  Once the angle from ground to KAP rig is known (via the clinometer) then the slide rule provides a proportional scale of plan distance vs. actual distance to the rig. The rangefinder can then provide either of these values as an input for determining the other.




A second approach based on scouts and radios

Lately I have started carrying a pair of Motorola Talkabout Plus radios in the KAP gear bag.  These tiny radios use the newly commissioned family resource frequencies and have a range of around a mile.  The technique here is simple.  I send one of my sons or a passerby downrange so that they can see my target from the side.  They then report back by radio to tell me how far downrange the KAP rig has progressed. 

The principal difficulty in this approach has been a reticence, particularly in strangers, to keep a stream of position comments coming my way.  Since I have the remote control radio and the kite reel in my hands I have not been able to respond to their comments readily and they soon quit talking.  I have to get a voice activated microphone to work around this.



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