As-Build drawings from Scan data are averaged and the differences or tolerance is in mm.
Errors still can occur in misaligned scans that are not registered properly or in the process of creating the 2D DWGs or 3D models as this is still a manual process where the scan data serves as a reference point.
With with laser scanned surveys you get even the information that other ways would be missed or unknown and even in most of the cases irrelevant. Sometimes less is more!
For example Architects don't like wobbly lines neither planning departments, in fact these applications may experience extra questioning and delays.
But on the other hand, where more is needed with scan data you have it and having more reference points at no extra cost of time or money, it is always a good deal!
We all know when dealing with real life and existing buildings, nothing is straight or with 90-degree corners; it can be 90.5°, 91°, or 89.2°, and no wall is 100% straight either. But this does not mean that the house will collapse or that there are any problems that needs to be addressed; you will always have small inaccuracies (mm), and this may be acceptable for smaller projects where the tolerance is not that strict.
These inaccuracies may be due to the finish of the walls, some due to the age of the buildings as with time they settle. There are various reasons for these small inaccuracies when we are dealing with existing buildings. But for projects that go through a complete refurbishment, these mm differences are usually of no importance as the property is stripped out completely in the process.
As a standard delivery, we follow these guidelines: Walls will be displayed as straight lines and angles averaged to fit the 90 degrees where designed this way unless requested by the client to follow the true angles and shapes, where walls and angles may not be straight.
Note: Anyone who conducts laser scanning surveys where necessary can follow these mm change in the structure where necessary as the scanners have collected the data.
Laser scanning cannot be compared to hand surveying; this would be a comparison between a bicycle and a car, which can travel further in a shorter time?
The traditional surveyor would have only one or a few measurements per wall to identify its location only. With laser scanning you can have measurements of every cm of the wall.
Here is a sample of the most affordable scanner Giraffe360Â that I have personally tested; it provides 2k scan points per one square meter.
But this is nothing in comparison to the capabilities of the Matterport Pro 3, which, in XYZ file format from Matterpacks, provides 8.3k points per square meter.
And the same Matterport Pro 3, in high-density point cloud file E57 format, provides even more points per square meter: 150k points per square meter.
While these numbers are HUGEe to understand, hopefully these images provided some visualisations of what we are discussing here.
Note: These two scanners are not even professional tools designed for scanning; they are more for property marketing (Check out my Youtube Review). When compared to professional tools, the accuracy goes to millimeters.
See Images below of Professional Laser Scanners capabilities.
For our day to day work, we use Leica BLK2GO for speed and efficiency. It is a handheld laser scanner that recreates spaces in 3D as you move, scanning over and under objects, through rooms and doorways, around corners, and up and down stairwells.
How accurate is the BLK2GO? The accuracy of the Leica BLK2GO is plus or minus 10mm.
Below is scan data from the BLK2GO (captured in 2 minutes).
For greater accuracy, we use the Leica BLK360 G2, it is a terrestrial laser scanner (TLS), which is a stationary system that scans a specific area from a fixed point. Once scanning is done, you have to move the scanner to the next location. This stationary scanning ensures greater accuracy.
How accurate is the BLK360 G2? The accuracy of the Leica BLK360 is plus or minus 4mm.
Below is scan data from the BLK360 G2.
This millimeter accuracy is crucial, especially for blocks of flats or high-rises. They must allocate the necessary resources, both money and time, for this level of detail to be safe to use. As construction progresses, deviations in walls or structural elements can be identified at an early stage.
And for this type of work there are even more accurate scanners available, as 4mm accuracy will not be sufficient.
Now that you understand laser scanning and its capabilities, it's time to answer your question. However, it begins with a question to yourself: What level of accuracy are you seeking?
There are tools and methods available for any level of accuracy, ranging from hand measurements with 1-5 measured points per wall to scans with millions of points of the same wall. The cost varies accordingly. Additionally, creating drawings or 3D models from scan data is a manual process, and someone will need to invest time, which translates to cost. And as important is the scan data the same importance has the drafting team and quality controls in place when it comes down to as-built drawings.
Based on our experience we have determined what works best for our clients and the projects we handle daily. We have established this as our standard to provide the best value for their money.
At SpaceSurvey, we construct or draw walls as straight lines and angles averaged to fit the 90-degree angles, unless requested otherwise to follow the true shapes and angles where walls and angles may not be straight.
If we notice any deviations from the original planned layout during this process, we inform the client and discuss potential adjustments.
So, when millimeter accuracy is necessary, inform your surveyor so they can utilize the right tools and follow the true shapes and locations of the existing structures in property.
Keep in mind that this may increase the time and cost of the project, but it is possible.
And if you found this information interesting, I have also created a YouTube video reviewing the two entry-level scanners, you may find the video interesting as well.
SpaceSurvey
Peter Bauman