In this tutorial, you will register scans to ensure that the scan captured by the scan station is correctly aligned with the overlapping scans from the station setups.
The Scan Station allows field surveyors to efficiently collect point cloud data without the need of a backsight or targets. To perform a scan station, set the SX10 in any location and in Trimble Access, simply select the scan station commend, the type of scan, and let the SX10 do the rest of the work. After the point clouds have been collected they can be tied to existing survey stations or other scan stations using the scan registration tool in TBC. Scan stations are a fast method of collecting scan data when the data does not need to be in a specific coordinate system or location.
To perform a scan registration, your project should include overlapping scans from both survey station setups, the survey station setups (total station with backsights) and the scan station setups which are free-standing scanners.
The purpose of the registration process is to move the scan station setups to align them with the non-movable, survey station setups, and then refine the registration by performing an additional adjustment of all of the scans to each other. We currently have several scan station point clouds that are not correctly referenced to the survey station data.
In the Point Cloud tab, you are going to launch the Scan Registration command. The registration command window contains multiple tabs: The first tab, Pairwise Registration is where scans are matched together - this will launch TBC into a different viewing mode. As shown here, the total station data with backsights are qualified here as reference stations. Then, as you can see on the right hand side, the scan that happened in the alley as a free-standing scan. That wall matches this wall here.
To better visualize your point cloud data you can use the rendering options to change how the points are displayed. True colour shows the scans colour relative to the images captured in the field. Because I stopped the colorization process during the import the clouds are displayed in default gray. If I switch to scan colour, TBC assigns each individual scan a colour. You can also choose region colour as a rendering setting, which will colour each region differently. Another option is to use the intensity based rendering. Many users prefer this options as it displayed key features in distinct colours and you can determine which features in the two scans that your registering, match based on the intensity.
First, I will perform the registration by automatic, which means using two scan stations. I simply select my reference stations and the moving station I want to register, in this case it is Q2, and click Automatically register pair. This will find the common point between a reference station and a moving station and will bring the two point clouds together. It is highly recommended that you visually check your registration and do not take the resulting numbers displayed here as a sign of good registration. In this case, the Residual area is small which is good, but the Overlap is very low. Click the Optimize Pair Registration to improve the results and visually check the registration. Typically, you want to focus on an area that has on overlap of green and red data and you can inspect how well they overlap.
You can see that these two scans fit together fairly well using the automatic registration. There are results displayed at the bottom of the command window for your registration.
The more point pairs you pick, the better pairing TBC will be able to perform. Once you have selected the point pairs, you can click the Optimize Pair Registration button, what this does is performs simple refinement on the picked point pair registration, and can help to better the results of the register.
Now that I have all of my scan stations registered as one point cloud, I can register these to the survey station - this will give me one dense point cloud. To do, I’ll select survey stations as a reference station, and the scan station as a moving station and use the automatically register pair as there is sufficient overlap in this project to register the scans.
Once this is computed, I can view the register error and overlap and visualize the results to see if the proper registration was performed. If I am happy with this, I can add to reference, and now my scans are one singular register group.
Once your registration is finished there is an option to perform an overall refinement on the registered clouds. This command performs the finishing touches on your registration. It allows you to fix one or more survey stations to perform the refinement. I’ll choose to fix all the survey stations and press, refine.
Moving out of the registration command back to the 3D and Plan view, the scans are now matched together and we can proceed with creating deliverables.
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