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How LiDAR works

Airborne laser scanning sends rapid laser pulses toward the ground and measures their return time. Combining range with precise aircraft position/orientation produces millions or billions of 3D points.

Returns​

One pulse can produce several returns. In vegetation, an early return may come from canopy while later returns can come from branches or ground. First return = canopy and last return = ground are useful intuitions, not universal rules.

Classification​

Point-cloud processing assigns classes such as ground, vegetation, building, water or noise. A bare-earth model is only as good as the ground classification. Dense scrub, cliffs, water, bridges and unusual built surfaces are common areas to inspect closely.

Point density​

Point density affects how much small-scale structure can be represented, but density alone does not determine accuracy. Flight height, scan geometry, GNSS/IMU quality, calibration, surface type and processing all matter.

Scan angle and flight lines​

Points near the edge of a scan can have different geometry from near-nadir points. Overlapping flight lines help coverage and quality control. Striping or offsets between lines can indicate calibration/alignment issues.

Accuracy​

Separate:

  • horizontal accuracy
  • vertical accuracy
  • precision within a surface
  • classification correctness

Do not infer centimetre survey-grade position because a DEM cell is 1 m wide.

New Zealand standard products​

LINZ's national aerial LiDAR specification requires 1 m bare-earth DEM and DSM products plus classified point clouds for programme acquisitions, in NZTM2000 and NZVD2016.

Continue to DEM, DTM and DSM and LINZ elevation data.

Last reviewed: 26 August 2026

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