Stadia Distance Calculator
Enter the stadia interval read on the rod and the vertical angle of the sight. The calculator reduces the reading to horizontal and vertical distance using the stadia constants K and C.
How to reduce a stadia reading
- Read the rod intercept between the upper and lower stadia hairs, in feet.
- Enter that interval and the vertical angle of the line of sight.
- Adjust the K and C constants if needed, then read the distances.
Examples
Level sight
interval = 1.5 ft, angle = 0
horizontal distance 150 ft, vertical distance 0
Inclined sight
interval = 2.0 ft, angle = 5 degrees
horizontal 198.48 ft, vertical 17.36 ft
Frequently asked questions
What is stadia tacheometry?
It is a fast way to measure distance with a telescope that has two stadia hairs. The rod intercept between the hairs is proportional to distance, so you read distance without a tape.
What are the stadia constants K and C?
K is the multiplying constant, usually 100, and C is the additive constant, usually 0 for modern internally focusing instruments. Distance for a level sight is K times the interval plus C.
How is an inclined sight reduced?
Horizontal distance is K times interval times cosine squared of the angle plus C cosine of the angle. Vertical distance is K times interval times sine times cosine of the angle plus C sine of the angle.
What does the vertical distance mean?
It is the rise or fall from the instrument axis to the point sighted on the rod. A positive angle gives a rise and a negative angle gives a fall of equal size.
Why must the stadia interval be positive?
The interval is a measured rod length between the stadia hairs, so it must be greater than zero. Zero or negative values are rejected.
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