Known limitations of the iMapper

Maximum range

7-25 m outdoors, depending on light conditions, angle of incidence and reflectivity of the surface finishing of the materials.
30 m indoors.

Accuracy

In depth, the measurement error is comparable to a good laser rangefinder: +/- 2 mm in depth for the iMapper Racer 2, slightly better for the Racer 3 (in laboratory conditions < 1mm).
This value depends on the number of photons sent back to the sensor, and can fluctuate depending on the angle of incidence, light conditions and texture, color and reflectivity of the target's material (white, mat material will send back more photons than a black, shiny material).

In normal conditions (99% of the time), the error is below 2mm. In bad conditions, usually, error will be bellow 5 mm. In most cases, it can be solved by putting a sheet of white paper (or painter tape) on the target.

The angular error is around 0.05 degrees (1/6400th of a turn). It is almost invisible, very slight undulations can be observed at grazing angle. It is a periodical error, so the wall go in the center of the sinusoid.

Other limitations

The iMapper is not waterproof!
The normal operating conditions are: less than 85 % relative humidity and a temperature between 5 °C and 32 °C (41°F to 89.6°F).
In front of a mirror, the iMapper may shut down if the laser beam returns directly to the sensor cell, which goes into safety mode (very rare).
If you go from a very cold (<0 degrees) place to a hot one (20 degrees), moist can form on lens, and the pictures will be blur.
iMapper 3 do around 10 measures per angular degree (a point every 0.8 mm at 0.5m, every 1.7 mm at 1m, every 8 mm at 5m)
iMapper 1 & 2 adapt their angular speed to the distance to get, when possible, a constant step size on the target. However, due to angular resolution of steppers motors, from a certain distance, the step size increase with distance.

After hundred of thousands of scans, we can confirm that the iMapper is highly reliable. Whenever we've had a doubt about a point cloud (e.g. one that didn't match manual measurements), the iMapper has always been right. The rare errors that can occur during assembly are generally due to poor handling:
Someone touched the iMapper during the scan.
The tripod was not stable (for example, one of the screws was loose).
There is an error in the assembly between points clouds.
The iMapper is not horizontal (creating small errors on vertical walls, but large ones on sloping walls (e.g. under a top floor attic)).
See more about this topic here:
Is it important that the iMapper is perfectly horizontal during a scan?
Scans are taken at different heights and walls are not vertical.
Drafting of areas on the platform were not done properly.

Updated on: 09/10/2024