Theodolites Were originally specialised optical instruments used for measuring terrestrial distances, angles and areas. The optics and precision of the instruments are highly accurate. Under clear skies and with competent operators, theodolites are slightly more accurate than GPS over the distance associated with a record altitudes. The traditional instruments are optical and the most recent instruments are about 20% optical/mechanical and 80% electronic. A major feature of the latest instruments is the ability to measure over 4 km using a laser beam with a sub 1cm accuracy. They can also measure angles with minute precision. Over a distance of 10 km even an older opto/mechanical instrument has a potential precision of under 10 meters. Irrespective of whether we use the theodolites on the field to measure altitude, we always use a theodolite to view the kite except on cloudy conditions. They are better than most telescopes due to their stability and excellent optics.
We no longer use theodolites for tracking, just fot viewing and GPS telemetry is very accurate and convenient. The major advantage is GPS provides live data instantly. Theodolites cannot be used when kites are above cloud and also require two qualified operators. I have learned a lot during the quest for the world record and I admire the precision engineering involved in designing and manufacturing these instruments. I have retained this page for anyone interested in these things and because it was an import part of all the information I learned over 15 years. Knowledge is never wasted.

Pentax laser theodolite. Using a bank of small reflective prisms, this instrument can measure the distance to a target over 4 km away with sub cm accuracy.
There is a specialised survey calculator that the 2 position kite data is imput to then it gives the kite altitude above the primary survey point (tether point).
This instrument was used in April 2005 to establish the reference survey points. The final survey was performed by an engineering surveyer specialising in terrestrial mining. Thank you Hugh Patterson.

This T16 Wilde is the "Rolls Royce" of optical Theodolites and although superseded by electronic instruments is still more than good enough to surpass all standards of accuracy for our record altitude measurement using optical instruments for triangulation, that is, if we were to continue to use them
The Achilles heel of the theodolite in the context of measuring kite altitude, is cloudy conditions, however, technically we are not supposed to fly near or into cloud so it is a moot point. Universal Instruments loaned us two instruments each year for the duration of the record attempts. The second drawback is that only qualified and experienced people should use them use them for official survey purposes but it is difficult to say if it would be acceptable for unqualified operators to use them to measure the altitude of kites for evidence of a world record altitude. Difficult, if not impossible to get 2 qualified surveyors to travel to a remote region on every series of attempts and to do it for free.

While it never became necessary to use theodolites and trigonomitry to measure kite altitude, the deveopment of the sytem at Cable Downs was very instructive, if not facinating, if you have an interest in trigonetry, mathematics and spatial engineering. While I don't regard myself as having any expertise in surveying, I can discuss my methods with survey engineers and understand the basic principles.
The calculation of the kite's altitude seems simple at first glance. Measure the kites flying angle (elevation) and measure the length of the kite line then apply the trig calculation, if the kite is at 50 degress and the line out is 100 metres, then 50sin x line length = 0.776 x 100 = 77.6 metres or 251 feet above the launch point. However, this would be wrong as he line is curved due to wind pressure and line weight.

The 3D diagram to the left represents an elevated view of a kite flying from it's tether point at K1.
K1 has a theodolite positioned accurately at the kite's thether point.
K2 has a theodolite positioned accurately at a survey datum, usually a metal peg hammered into the ground
K1 to K2 (line G1) is a known distance either measured by a theodolite, laser or GPS coordinates
The angles A1 and A2 are measured from the kites viewed by the theodolite.
The kites elevation A5 and A4 is measured by both theodolites.
V is calculated using combine formula and the ratios of sin, cosine and tangent.
The straight line distances from both theodolites to the kite can be calculated from the distance G1 and applying to the hypotenuse H1 and H2.
The line sag (red) can be calculated from line angle, kites elevation and line out.
However, both readings must be simultaneously coordinated by using mobile communication devices as the kite is always moving, however slightly. Each theodolite operator must be experienced and qualified. Kite altitude by theodolite is more akin to astronomy. It proved too complex and unworkable on cloudy days but facinating none the less. The method below is a hypothetical method that uses some of these methods.
The survey datums were established by mining surveyor, Hugh Paterson. He used a Trimble Total Station which has augmented GPS and laser targeting plus the optical capabilities of traditional theodolites. There were five bench marks established, each located by a steel peg driven into the ground, centre drilled and marked with reflective paint. these datums were accurately establishing withing a few centimetres. The first point was at the kites, tether point B (the trailer winch) about 100 metres from the eastern end of the air strip. The second point 4 was at the western end of the air strip, 1.1 km away. Point 2 was near Cable downs entry gate on Louth Rd Point 3 and 4 were on the Louth Rd, 6 km apart. Point 5 was to the west 5 km from point B
It's not important that they be established at nominal distances but that they are very accurately position and the position is known plus have a wide enough spread to reduce angular error and to allow viewing at lower angles within the instruments field of view.