How to Capture 6mm High-precision Point Cloud with Mobile Sc

Release time：2021-01-25 11:55viewed：times

How to Capture 6mm High-precision Point Cloud with Mobile Scanning Devices.

Today's mobile scanning devices scan fast, can scan large space, and can generate accurate high-quality point clouds, which is suitable for projects with very strict requirements on the quality of point clouds.

It is generally believed in the industry that mobile scanning devices can speed up the capture workflow and help customers develop their business. However, what we may not know is that the best mobile scanning system available today can meet the requirements of very demanding fil-building projects and generate extremely accurate point clouds.

Next, we will show you how this is done.Here is a quick overview of how to use mobile scanning device to achieve accuracy of 6 mm (or higher).

Moving Scan Best Practices
Because these devices capture point clouds when moving, they are prone to small errors that degeade the quality of point clouds. Fortunately, the functions provided by today's mobile scanning devices can help correct these errors and ensure the highest possible accuracy.

Closed-loop scanning
Closed-loop scanning is an industry standard supported by most mobile scanning devices, and for small scanning items, this is usually all we need.

To take a closed-loop scan, return to a position that has been scanned. SLAM (Synchronous Location and Map Construction) algorithm will identify this location and automatically optimize the point cloud to correct errors and improve accuracy.

The optimization of anchor points
Only a few advanced mobile scanning devices on the market provide anchor point optimization. This feature is optional for many scanning items. Because for smaller scanning items, we can achieve high precision through closed-loop scanning. However, when scanning large construction assets, it will become crucial because it corrects the drift error of the point cloud that might result from a long-time scan.

We implement this function in different ways. To use the anchor point optimization with NavVis scanning equipment:
You need to add control anchors to the entire asset and record their coordinates using a total station. When scanning, the NavVis scanning device is used to capture the control point. During data processing, the measured coordinates of each control point are input, and the software will use this information to optimize the point cloud and improve its accuracy.

Proof From the Field
Now, let's demonstrate how to use closed-loop scanning and anchor points to improve the expectation of the accuracy of scanning data. To do this, we will show two Scenario tests with Navvis's wearable mobile scanning device NavVis VLX.

Small Scan Using Closed Loop
In the first test, the NavVis team scanned a part of an ordinary office building. They chose this environment because the combined scanning of rooms and corridors is a challenge for mobile scanning equipment. In other words, it may produce errors that need to be corrected. Become of the small size of the scan, the team chose closed-loop scanning (but did not use anchor points) to optimize the point cloud and eliminate drift errors.

Small scan test conditions:
Area: 460 square meters
Scanning time: 30 minutes
Anchor: 0

To seek truth from facts, NavVis used total station to scan the office. The supplier team manually measured the distance in the total station scan results and compared it with the same distance in the moving point cloud.

Results:
It has proved that closed-loop scanning can effectively correct the errors in this small scanning.
22 out of 24 locol measurements within 5mm accuracy(compared to mapping data)
The remaining 2 local measurements were within the range of 6 mm and 10 mm

Large Scans Using Anchors
In the next scan test, NavVis team chose to scan the parking lot. Become of the large building area, they know that the last point cloud is likely to have drift errors. In order to correct this error, they used a combination of closed-loop scanning and anchor point optimization.

Large Scan Test Conditions:
Area: 1500 square meters (large)
Scanning time: 20 minutes
Anchor: 8

The team optimized the data in two ways: one was to use only closed-loop scanning, and the other was to use both closed-loop scanning and anchor points. Finally, they compared the two data sets with the station scanning results of the commissioned local supplier.

Results:
Anchor optimization proves to be very effective in reducing drift error.
Closed-loop scanning: 8mm absolute accuracy
Closed-loop scanning and anchor optimization: 6mm absolute accuracy

Wrapping Up
From the data provided above, it is clear that closed-loop scanning and anchor point optimization can help us generate very accurate point clouds.

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How to Capture 6mm High-precision Point Cloud with Mobile Sc

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