Top 3 Ticks & Tricks – 3D Laser Scanning in Measured Surveys
Have you just started working with Terrestrial 3D laser scanner or trying to get some more useful tips on how to make the process faster & more accurate?
Guest Author: Chris Alby, specialist with over 5 years of experience working in laser scanning. See the following – Measured Building Surveys
We completed hundreds of Commercial & Residential projects various sizes and complexities and would like to share what made our Scanning & Data Processing easier and faster.
3D laser scanning settings
The main point to remember is that:
- Resolution = The distance between two points ( i.e 1.5mm @ 10m )
- Quality = The number of times a scanner shoots a laser in the same spot to calculate the mean coordinate figure of that point.
When it comes to resolution settings, the main rule is Greater Distance = Higher Resolution. Below are the settings we use for our scanner for the majority of our survey:
Indoors : Black & White – Quality x3 & Resolution 1/8 – 12.27mm @ 10m
Outdoors: Black & White- Quality x2 or x3 & Resolution 1/4 – 6.14mm @ 10m
You can scan in color too which will make your point cloud look much more appealing but would also increase the scanning time of around 4min per scan.
Use Targets
Although there are multiple ways of registering a point cloud, we found using targets will never harm, but at times may be crucial for successfully registering a cloud. For our purposes we found using spheres is the quickest and easiest option. As we use Faro scanners, we use Faro Scene for processing & registering the data. Although we aim to use the Automatic registration mode available in Scene, when a project is large, it will be impossible for the computer to automatically put together all scans in one go. Therefore the registration is done by breaking the project into different parts and using targets is the best way to stick those parts together when putting the all parts into one piece.
As 3D laser scanners use x,y,z coordinates, it is best to put three spheres in each locating into a triangle shape, keeping between minimum 0.5m (indoors) & maximum 3m (outdoors) distance away from each other.
Scanner Positions
Before trying to figure out the best route for scanning, you need to understand the principle of how the software operates when registering the scans together to make a point cloud.
The principle is simple:
the software overlaps two scans and looks for the common points that overlap each other.
The golden rule is: More common points between scans = more accurate registration process.
Taking the above information into account, we usually position our scanner as follows:
1) Distance between scans = No further than 3-5 metres inside & 5-10 metres outside
2) Doorway scan = always put a scanner in the doorway to maximise the number of overlapped points & make sure two rooms align correctly.
