Side Shot Coordinate Calculator
Set up your station and backsight once, then add as many side shots as you took from that setup — each gets its own computed easting, northing and elevation.
Field aid, not a certified result. Verify against known control before relying on these coordinates for design or recording.
Station setup
Backsight
Vertical angle convention
Side shots
| Point | Azimuth | Bearing | Horiz. dist. | Easting | Northing | Elevation |
|---|
How a side shot becomes a coordinate
Quick answer: From a known station and a known backsight direction, a total station’s horizontal angle and slope distance to any target point are enough to compute that point’s easting, northing, and elevation — a calculation called a side shot or radiation.
The horizontal clockwise angle read from the backsight, added to the azimuth of the backsight itself, gives the azimuth to the target. The slope distance and vertical angle split into a horizontal distance and a vertical (elevation) component. From there, the target’s easting and northing follow from the horizontal distance and azimuth, and its elevation follows from the station’s elevation, the instrument height, the vertical component, and the target height subtracted back out.
Because every side shot from one setup shares the same station and backsight, only the angle, distance and vertical reading change from point to point — which is why field books record dozens of shots per setup and why this calculator handles them as a batch rather than one at a time.
Elevation formula
Elevation of target = Station elevation + Instrument height + Vertical component − Target height
Vertical component is positive upward. With a zenith angle, it’s Slope Distance × cos(Zenith); with an altitude angle, it’s Slope Distance × sin(Altitude).
Frequently asked questions
What’s the difference between zenith and altitude angle?
Zenith angle is measured from straight up, so 90° is level and 0° points at the sky — this is what most total stations display directly. Altitude angle is measured from level, so 0° is horizontal and positive values point upward.
Why do I need a backsight?
A backsight establishes the reference direction your instrument’s horizontal angle is measured from. Without it, a horizontal angle reading alone has no fixed direction in the real world.
What is instrument height and target height for?
Instrument height is how far your total station’s optical center sits above the station point; target height is how far the prism or rod sits above the ground at the point being shot. Both are needed to get the target’s ground elevation right, not just the instrument-to-prism difference.
Can I use this for a 2D shot with no elevation?
Yes — leave elevation, instrument height, target height and vertical angle at zero (or set vertical angle to 90° zenith / 0° altitude) and the easting and northing will still compute correctly.
Does the order of side shots matter?
No. Each side shot is computed independently from the same station and backsight, so they can be entered and reviewed in any order.
Does this replace field-book review or a licensed survey?
No. This is a calculation aid. Always review raw field data and have any survey intended for legal or design use checked and certified by a licensed surveyor.
