Level of Accuracy
Customers don't need to be experts when it comes to laser scanning but they should have some familiarity with what is involved when dealing with laser scanning providers.
One of the biggest hurdles facing the laser scanning industry is not having the client and service provider on the same page when it comes to deliverables. It is of the utmost importance that both parties have the same expectations coming into a project. Most customers aren't familiar with laser scanning and it is up to the provider to make sure the intent of the customer is understood. Defining intent helps identify the acceptable methods and processes which can be used to achieve the desired results.
There are no laser scanning governing bodies or standards in Canada therefore most providers have adopted the USIBD (U.S. Institute of Building Documentation) as an unofficial authority in determining what is acceptable as far as the levels of accuracy (LOA). The USIBD breaks up LOA into five range categories.
LOA10 - 5cm to 15cm
LOA20 - 15mm to 5cm
LOA30 - 5mm to 15mm
LOA40 - 1mm to 5mm
LOA50 - 0 to 1mm
These categories are specified at the 95% confidence level as the surveying industry standards.
Laser scanners are not perfect. Every scan carries a small error. And over many scans these errors can accumulate. This is why the measurements of objects within a small cluster of scans will be more accurate than where a certain object is relative to the building. For example, the door frame measurement will be more accurate than the location of said door within the building itself. Especially when dealing with very large areas. Environmental factors and the type of objects being scanned also affect the accuracy of laser scan data. Fog, rain, snow, dust, and pollution can affect the accuracy of the laser scanner. Even the object's material or angle can sometimes affect accuracy.
3SIXTYEDGE provides an LOA40 at 10m for measurements taken within small clusters of scans and aims for an LOA30 for the overall point cloud on most projects. Independent measurements are taken with a separate laser measuring device to validate these levels of accuracy.