What it does
Excavation records place every find, sample and level on the site grid. This page does the sums for you as you record, and gives you a clean sheet at the end:
- Grid squares: from the grid origin and square size, each point gets its square, named by the square’s south-west corner (E1010 N5020) or by letters east and numbers north (C5).
- Positions three ways: type the grid easting and northing; measure offsets east and north from a peg; or measure along a baseline between two pegs and at right angles to it (right of the line is +, left is −).
- Heights from a level: give the datum height and the backsight on it once; each staff reading then becomes a height. You can also type heights, or leave them out.
- Trench check: whether each point lies inside the trench.
- Latitude and longitude: tie the grid origin to a latitude and longitude, and give the bearing of grid north if the grid is turned. Every point then gets its own latitude and longitude.
- Phone GPS (optional): press Use my location, and the browser asks your permission. The fix (with its accuracy) is kept with the next point; if the grid is tied to latitude and longitude you can also place the point on the grid from it. Phone GPS is good to a few metres at best, so it suits survey points and surface finds, not finds in a trench.
Nothing is stored or sent. Points live only in this page, so download the CSV or the PDF sheet before you close it.
Worked example
Press Use the example. It sets a made-up grid with origin E 1000, N 5000 and 5 m squares, Trench 1 of 4 × 2 m with its south-west corner at E 1012, N 5021, a datum of 100 m with a backsight of 1.42 m (height of instrument 101.420 m), and the origin at 45.5° N, 73.6° W. Six points are added:
- F1 at E 1013.250, N 5021.800 with a staff reading of 1.87 m: height 99.550 m, square E1010 N5020, latitude 45.5001961, longitude −73.5998305.
- F2 from the peg at 1012/5021, 2.40 m east and 1.15 m north: E 1014.400, N 5022.150, height 99.470 m.
- S1 on the baseline from 1012/5021 to 1016/5021, 3.10 m along and 0.60 m to the left: E 1015.100, N 5021.600.
- L1 and P1 (a level and a section peg), and F3, a surface find at E 1008.600, N 5017.200 in square E1005 N5015.
The sheet reports 6 points: 5 inside Trench 1, 1 outside, and draws the plan with the grid, the trench and each point by type.
Tips
- Use a false origin (such as 1000/5000) so all coordinates stay positive.
- Measure offsets with the tape level and square to the grid; for long offsets a baseline is easier to keep square.
- The latitude/longitude tie is only as good as the origin’s coordinates. A hand-held GPS reading of the origin is off by metres.
FAQ
How accurate is the latitude and longitude? The sums are within a millimetre of the full ellipsoid answer up to 1 km from the origin. The real limit is how well you know the origin’s position and the grid’s rotation.
Is my location stored? No. It is asked for only when you press the button, it stays in this page, and it is lost when you close or reload it.
Where the numbers come from
- Baseline-and-offset and levelling (height of instrument = datum + backsight, height = HI − foresight) as in standard field survey practice. Grid to latitude/longitude by Puissant's short-line formulas on the WGS84 ellipsoid (a = 6378137 m, f = 1/298.257223563), using the meridian and prime-vertical radii of curvature.
- Checked against Vincenty's direct formula on WGS84, written separately in Python: 40 random cases up to 1 km from the origin at latitudes up to 60° agreed to better than 0.03 mm per metre (under 1 mm at 1 km); the inverse returns the grid point to 1e-9 m.
- The example grid, trench, points and origin coordinates are made up for this tool.
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Last updated 2026-11-09.