The Site Control Module for Trimble Field Link is an add-on to the Advanced Feature pack and is available to any data collector running Windows 10. In summary, the Site Control Module (SCM) is just another way of creating and collecting additional control points. Specifically, it is used to gain confidence when creating ‘primary control’ for a jobsite. For 99% of subcontractors, this is not necessary. The everyday user of Trimble Field Link is able to set up their robot from either property corners, column offsets, grid intersections, formwork offsets, anchor bolts, or any other existing points that exist both in the real world and can be created in the tablet. If none of those points exist in your project, we have a workflow for you!

SCM Image 1
SCM Image 2

Step 1: Robot is set up at what they call a “base point” which is either the property boundary or a known distance from the property boundary. Everything on a jobsite is built from the base point. They then dial in what they call a “zero azimuth”, which is just another term for a straight line. They know distance doesn’t really matter, they need to know what it is. They simply connect to the robot, walk away from the robot while looking at the device, and turn to check what their angle and distance is. Then they create two points that far apart in Trimble Field Link (from Create -> Plan). Moving forward we will call the “base point” CP1 and the “zero azimuth” point CP2. The SCM then will guide contractors on how to create the rest of the property boundary points. Below shows then end result of what we are aiming to accomplish.

SCM Image 3

You may be thinking why we don’t just complete a resection, set up with your robot in between all 4 points, and use the Measure -> Collect feature to add CP3 and CP4 to the map. Well, the reason is that this site control module is doing that same thing by using generic survey workflows. The reality is that surveyors live in constant fear that they are not measuring correctly and want a way to mitigate errors when measuring. In order to explain this, let’s take CP3.

Step 2: After step 1 is accomplished and you have a zero azimuth/distance established, you will then move your robot to CP2, set up over it, and bring your prism to CP1. Please note here that the user will need 2 different prisms to make this work because you also need a prism set up over wherever CP3 should be when you start. The user needs to select the “New Traverse Point” option from within the setup screen. The program will ask you to select which point your robot is set up over. You will tap CP2. Then it will ask for a “backsight.” Tap on CP1 and select “Shoot.” Then it will ask for a foresight. You will then turn the robot physically over to CP3, and select “Shoot.” The robot will then go back and forth between CP1 and CP3 calculating the angle and distance between the shots. It then stores a coordinate on-screen for CP3. We aren’t done yet!

Now you need to disconnect, move the robot to CP3, and set up over it. Additionally, you will need to move your 2 prisms to CP1 and CP2. Reconnect to your robot through Trimble Field Link and select “Set Up” again. This time, make sure you select “Existing Backsight” because you already have all the points on the screen that you need. The program guides you through this; however, the verbiage can be pretty complicated.

When it asks for a backsight, you will select CP2 and your foresight will be CP1. The robot will repeat these measurements several times, calculating the angle and distance between CP1 and CP2. Finally, you will move the robot back to CP1. CP3 will be your backsight prism and CP2 is your foresight prism. Again, select “Existing Backsight,” then “Foresight,” and shoot those two prisms. This completes a full circle of all currently existing control points with known angle and distance measurements for all of them (shown below). The key is that all 6 angle and distance measurements are independent measurements rather than relying on 1 single good resection.

SCM Image 4

Step 3: The order of operations about which point is the foresight and which is the backsight is pretty important here. There is a lot of walking around, moving prisms, and moving robots. It is VERY time-consuming. What this does for us, however, is that all the angles are calculated from each point rather than just one. Additionally, users have the ability to shoot “face 1” and “face 2” shots. This will average the distance reading when shooting the distance from right side up (face 1), as well as upside-down, flipped over, and aimed at the same prism (face 2). Again, this just averages these readings. Trimble Field Link calls this “shooting rounds”.

After you finish shooting all this, you have completed a “traverse” to establish CP3. Trimble Field Link has a special report showing differences between the angle and distance on all 6 of these shots and actually adjusts the coordinate of CP3 based on the differences shot. The process is repeated for CP4 as shown below.

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