Whether you are looking at buying a system for yourself or subcontracting a mobile mapping survey, choosing the right scanner is vital to achieving a successful survey project.The laser sensor is just one component of the overall system. We have found that it is highly beneficial to review what type of survey projects you wish to carry out and if the system you are considering uses a scanner that can meet all of those needs.
Top ten things to consider:
- Effective measurement rate – how many usable points are emitted from the scanner (be careful not to confuse this with Pulse Repetition Rate (PRR) which defines the total number of points emitted by the scanner, regardless of whether they can be used or not.
- Range – the furthest distance the scanner can see and therefore the furthest distance you can measure to
- Rotation/mirror speed – how many scan lines are measured per second. If you want to walk/drive or fly quickly and require a uniform grid point spacing then you will most likely need a scanner with a fast rotation speed.
- Accuracy and precision (also known as noise or repeatability) – this is a common source of confusion when looking at scanner specifications. Different scanner manufacturers or Mobile Mapping System providers can often use these terms to mean different things. Fortunately, for most scanners the accuracy and precision are often very similar values so you could find that only one is stated in the specifications.
- Relative Accuracy – this term has never been rigidly defined but think of this as a combination of both scanner accuracy and precision – more on this here
- Field of view (FOV) – For mobile mapping systems a FOV of 360 degrees is optimal so there is no missing data from your scene. For scanners with a FOV less than 360 deg you might want to look at systems with more than one scanner to capture all the data. For applications where only part of the environment is required, such as road surface mapping or mapping from a boat then a scanner with a limited field of view will suffice.
- Intensity & Reflectivity – the intensity of the data decreases with range and the angle of incidence which can lead to a non-uniform intensity in the pointcloud. This effect can be reduced by some scanners that are calibrated to take range into account and the intensity is thereafter referred to as reflectivity – this enables you to identify features in the pointcloud better.
- Multiple target capability – not all scanners have this feature so if you are keen to penetrate vegetation and generate a richer pointcloud – this is a useful feature to have.
- Ruggedness – very important for mobile mapping because the scanner will likely be subjected to harsh conditions such as rain, snow, smoke, dust and loose gravel, all of which can cause damage. Does the scanner you are considering have a mirror? Due to the sensitivity of scanner mirrors, we wouldn’t recommend this type of scanner for mobile mapping.
- Price – what is the overall cost of the scanner? Consider costs such as servicing, warranty, technical support, down-time of the system when the scanner is being serviced, frequency of servicing etc.
The table below lists some typical mobile mapping applications and some recommended scanner features:
|Highway Surveying||Tunnel Mapping||Coastal Mapping (on a boat)||Asset Mapping|
|Scanner Type||TOF or phase||TOF or phase||TOF||TOF|
|Effective Measurement Rate||>500kHz||>500kHz||>500kHz||>100kHz|
|Field of View||180||360||60||360|
|Multiple Target Capability||No||No||Yes||No|
For more information about Choosing the Right Scanner download our Mobile Mapping Buyers’ Guide here.