How to Use Laser Survey on RTK GNSS: AP30 & AP40 Field Guide

The laser on AP30 Laser and AP40 Laser+ solves one problem: the pole tip cannot reach the point you need to measure.

Inaccessible Measurement Points. Building corners across busy roads, pipe inverts across drainage channels, bridge abutment faces, utility poles on the far side of a fence, wall faces in confined spaces. Without laser, these points require unsafe access or a separate total station setup. With laser, you measure from a safe distance in seconds.

Slope and Embankment Survey. Road embankment toe and crest, quarry bench faces, batter slope faces on cuttings — surfaces that cannot be safely accessed with a pole. The laser measures the face from the bench or carriageway.

Laser Stakeout Offset. Setting out a design point that falls inside a wall, under water, or on a surface where a physical mark cannot be placed. The laser calculates the offset position from the receiver to the design point and guides you to the correct standoff distance.

The Camera Role. The front-facing camera on AP30 and AP40 Laser+ is not for photography — it provides the live aiming view on the controller screen. You see the target through the camera feed with a crosshair overlay and fire the laser precisely at the point to be measured.

When you fire the laser in ApekSurv, the software combines four measurements to calculate the target's 3D coordinate:

1. RTK Position of the GNSS Antenna. The receiver's Fixed RTK position at the moment of laser firing — ±8 mm horizontal accuracy.

2. Pole Height. The vertical distance from the ground to the GNSS antenna phase centre, entered in ApekSurv before the session. Errors in pole height become errors in every laser measurement — enter it precisely.

3. Laser Distance. The measured distance from the laser emitter to the target surface. AP30: ±(8 mm + 5 mm/m) within 30° tilt. AP40 Laser+: same accuracy specification.

4. Laser Aiming Angle. The horizontal and vertical angle of the laser beam relative to the receiver, measured by the IMU at the moment of firing. The 120° IMU records the receiver tilt precisely so the angular offset to the target is computed correctly.

ApekSurv combines these four values in real time and outputs the target's easting, northing, and elevation directly — stored in the project file alongside your standard RTK observations. You see no maths; the result appears on screen within one second of firing.

Stabilise the receiver before firing. The IMU records receiver tilt at the moment of laser firing. Any movement during firing introduces angular error into the coordinate calculation. Rest the pole against your body, a vehicle, or a solid surface. On windy days, shelter the receiver before firing.

Use zoom on the camera feed. ApekSurv allows digital zoom on the camera feed for precise crosshair placement on distant targets. At 80–120 m (AP40 Laser+), zoom in before firing to confirm the crosshair is on the exact target point.

Bright sunlight aiming. Green lasers are significantly more visible than red lasers in daylight. In direct equatorial sunlight at long distances, shade the target surface with a hand or hat to make the green dot visible for visual confirmation of aim.

Multiple shots on critical points. For important points (building corners, boundary marks, structural features), fire three times and compare the three coordinate results. If all three agree within 20 mm, accept the average. If one result differs significantly, it likely reflects off a wrong surface — discard it.

Tilt within 30°. Laser accuracy is specified within 30° of tilt. For near-horizontal laser shots (aiming at a wall at the same height as the receiver), tilt is minimal. For steeply angled shots down a slope or up a building, minimise tilt where possible.

Laser Accuracy Specification: ±(8 mm + 5 mm/m) within 30° tilt angle. At 10 m: ±58 mm theoretical maximum error from laser alone. At 30 m: ±158 mm theoretical maximum. In practice, careful aiming and stable receiver position typically achieve ±20–50 mm at typical survey distances.

RTK Component: The RTK Fixed position of the receiver contributes ±8–15 mm to the total error. On short baseline Base+Rover deployments, this is typically ±8 mm.

Total Error Budget: For a 20 m laser shot with good technique, expect ±20–40 mm combined accuracy. Sufficient for detail survey, as-built documentation, and offset stakeout. Not sufficient for precise structural setting-out at ±5 mm tolerance — use a total station for that.

Limitations: Laser cannot penetrate glass, water, or mesh. Transparent or highly reflective surfaces may return false readings. Maximum range is reduced in rain, dust, or haze. Dark matte surfaces absorb more laser energy — range may be reduced on very dark targets.