Measure a corner you can't occupy

Offset shots for a pin in a fence line or under a tree. Occupy a clear spot, then key a bearing and distance, or tape from two spots.

On this page

Some corners can't be occupied: a pin in a fence line, against a building, or under a tree that blocks the sky. An offset shot measures a clear spot nearby and computes the corner from what you tape to it. The app reduces it on the project grid and keeps everything you entered on the point.

There are two methods:

  • Bearing & distance: one occupied point, and the bearing and distance from it to the corner.
  • Two distances: two occupied points, and a tape from each to the corner.

Before you start

  • A projected coordinate system for the project, so the offset is reduced on its grid and you can key a grid bearing. Without one, the bearing is read as true.
  • A tape, and for Bearing & distance, a way to get the bearing: a plat, a line you can turn from, or a compass corrected for declination.

Start an offset shot

  1. Choose the type you're collecting and tap ⊕ on the Survey map, as for any point (see Collect a point).
  2. On the Capture position sheet, switch on Offset shot.
  3. Stand on a clear spot near the corner and capture it. With a receiver, tap Capture occupied point or Average multiple samples…. On phone GPS, use Capture (30 s average) or Quick capture (single fix).
  4. The Offset shot form opens, with the Occupied point's coordinates, accuracy and elevation at the top.
  5. Choose Bearing & distance or Two distances.

Tap Back on the form to return to capture and occupy the spot again.

Offset shots are for points. They aren't offered when you're collecting the vertices of a line or an area.

Bearing & distance

  1. Under To the corner, type the Bearing: a quadrant bearing such as N 45-30-00 E, or an azimuth such as 45.5.

  2. Under North, choose Grid or True:

    • Grid for a bearing read off a plat, or turned from a grid line. It's the zone's grid north.
    • True for a bearing from a sun shot or a GNSS-derived line.

    The choice appears only when the occupied point is inside the project's zone. Otherwise the bearing is read as true, and the footer says why.

  3. Type the Distance: the horizontal distance to the corner, as the tape reads held level.

  4. Check the Tape unit: m, ftUS or ft. It starts on the zone's unit.

  5. Optionally type a Δ height: the corner's height minus the occupied point's. Leave it empty and the corner has no elevation.

  6. Check the Corner: its latitude and longitude, Northing and Easting in the zone's unit, Elevation, and the True bearing when you keyed a grid one.

  7. Tap Use this point, then fill in the form as for any point.

A bare number is read as an azimuth, and an orange note reminds you to write N 45-30-00 E if you meant a quadrant bearing. The footer also says how far a 1° bearing error moves this corner, so you can judge how carefully to read the bearing.

Two distances

Use this when there's no bearing to be had. The corner is where two taped distances cross.

  1. Under First tape — from the occupied point, type the Tape distance from the first occupied point to the corner, and check the Tape unit.
  2. Walk to a second clear spot, well away from the first. The tapes are strongest when they cross the corner near a right angle.
  3. Under Second tape — from a second point, tap Capture second point. The section shows its coordinates and how far it is From the first. Tap Occupy it again to re-capture it.
  4. Type the second Tape distance.
  5. Under Corner is, choose Left of first → second or Right of first → second: which side the corner is on, looking from the first point toward the second. Two circles meet in two places, so the app won't choose for you.
  6. Optionally type a Δ height: the corner minus the first point.
  7. Check the Corner: its coordinates, Northing, Easting, Elevation, and Tapes cross at, the angle between the two tapes at the corner.
  8. Tap Use this point.

The app refuses two cases:

  • The two occupied points are less than half a metre apart.
  • The distances can't meet. The message says how far they miss by: check both tapes, and that you occupied the right spot second.

How the corner is computed

The occupied point is projected onto the project's grid, the taped ground distance is scaled onto the grid, and the corner is computed there, the same way COGO → Traverse works. A grid bearing is applied directly. A true bearing is turned to grid by the convergence first.

The accuracy recorded on the corner is the occupied point's, or the worse of the two for Two distances. The offset's own error, mostly the bearing or the tapes, isn't estimated or added to it.

What the app records

The corner is saved like any collected point, with the occupied point's measurement record. On top of that, it keeps:

  • Bearing & distance: the occupied point, the bearing exactly as keyed, grid or true, the distance with its unit, and the height difference.
  • Two distances: both occupied points, both tapes, the side and the crossing angle.

That's enough to recompute the corner from the field notes. It appears:

  • on the asset, as Offset shot under Positioning detail, for example 12.400 ftUS at N 45°30'00.0" E grid from the occupied point,
  • in the CSV export and the bundle's data.csv, in the offset column, and in GeoJSON as an offset property,
  • in the QA report, as a note counting the offset shots and giving the longest offset.