Scan Import and Station Sampling Options in Trimble RealWorks
Welcome back for another Scanning Tip of the Week. This week’s entry looks at point cloud import and station sampling options for Trimble® RealWorks®.
The start of every Trimble RealWorks project begins with bringing your point cloud data into the software. First, let’s go over three ways to import your scan data.
Point Cloud Import
The first option is using the Import tool found on the Home tab of the ribbon. Click the dropdown and select Open.
A File Explorer window will open, allowing you to locate the project data you wish to import. For this example, a project with a TDX format was selected. (Note: Trimble RealWorks allows for a wide array of file formats that can be used during this step.) With your data selected, Trimble RealWorks will prompt you to save your project as an RWP.
Once the file path and name are determined, a processing window will appear with a number of options. The first section is for station sampling, a topic that will be discussed in detail later in this article. Some filtering options allow you to sample points by range or intensity values. And an option to export your panorama images as JPEG files can be selected.
Import and Register
The second import option is using the Import and Register tool on the Home tab of the ribbon.
As with the previous Import tool, a message will prompt you to save your project as an RWP. Once saved, a window will appear to allow the selection of the project files.
In this example, I used the Select Files… button to browse for my project TZF files. (Note: This operation can be completed with .tzf, .ptx, .fls, .zfs, .e57, .rsp, .tzs, and .tos file formats.)
After selecting all project files, click Next > to move to the Extraction Options. Here you can choose your station sampling and filtering options as mentioned earlier.
The last step of this process is the Registration Options. Here you can select Auto-Register using Planes (Targetless) or Auto-Extract Targets and Register. If your project contains spherical or black and white flat targets, select the second registration option and input your specific target sizes. If your project does not contain targets, use the targetless option.
Drag and Drop Import
The third import option is the classic Drag and Drop method. Open a File Explorer window on your computer, select the files you want to import, and drop them into the Trimble RealWorks window.
This method will not prompt you to save your project or select station sampling options. Instead, a default project name will be given in the WorkSpace section and the stations will appear with no sampled points.
So now that you have your scan stations imported, what is station sampling, and what options should I choose?
Create Sampled Scans
To explain station sampling, let us continue with the Drag and Drop import from above. The explanation of the sampling options can be applied to the Import and Import and Register methods as well.
Select the project in the upper WorkSpace window, or all of the scans in the lower WorkSpace window you wish to sample. Next, click on the Create Sampled Scans tool on the Home tab of the ribbon.
This will open a window similar to those from the earlier import options.
Here we can finally discuss the sampling options available to you. These include Sampling by Step, Spatial Sampling, Spatial Sampling (Keep Details), and Generate a Preview Scan.
The option containing the fewest number of sampled points is the Preview method. Preview sampling provides a sufficient amount of points to register your stations while minimizing the size of your project.
Another option is to use Spatial Sampling. This method applies a homogeneous sampling across each scan using a user-defined value. This choice will remove move points in high density areas, but less in low density regions.
Spatial Sampling (Keep Details)
A variation of the Spatial Sampling option is the Spatial Sampling (Keep Details) method. This option samples all points at high contrast areas, such as edges, and a user-defined spatial distance for low contrast areas, such as walls or floors.
Sampling by Step
The final option is Sampling by Step. This applies a ratio of sampled points based on a user-defined value. For example, a step value of 1 means a 1:1 ratio. For every 1 point in the scan, 1 point is sampled, or all points are sampled. A step value of 2 means a 2:1 ratio. For every 2 points in the scan, 1 point is sampled.
With everything discussed so far, you may be asking, “Can I sample certain areas of my scans at different amounts?”. The answer is “Yes!”, and we can quickly go over two methods.
This first option for station sampling uses the Scan Explorer tool, found on the Home tab of the ribbon.
A window will open showing a station based view of a project scan. You can change the view to another station, select different rendering options, or extract points. Other tools exist within the Scan Explorer and may be revisited in a future article. For now, select the Extract Points tool.
A number of extraction tools become available allowing you to select a region with a rectangle or polygon, extract a plane, extract a cubic region, or extract the entire station. You can apply the selection to all stations, and can determine the sampling options from All Points, Spatial Sampling, and Spatial Sampling (Keep Details). In this example, the Polygonal Area tool was used and All Points were selected.
Selecting the Create button will process the point cloud sampling of the selected area and will create an object in the Production mode of your project. This object will only contain the sampled points within your determined boundary.
Limit Box Extraction
The final tool for this Tip of the Week is the Limit Box Extraction tool, also found on the Home tab of the ribbon.
This tool will allow you to create a limit box around the area of the project you wish to extract. It has the same functionality as the regular Limit Box tool, but has an additional sampling feature.
Move the bounds of the limit box to envelope your target area, select your sampling method, and click Extract points from TZF Scans. As with the Scan Explorer extraction, an object of the bounded scans will be created within the Production mode of your project.
Choosing the right sampling options will allow you to visualize the key parts of your project while keeping the project file size to a manageable amount. Let us know if you have any tips and tricks for station sampling and as always, keep on scanning.
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