Module 7 Defining Coordinate Systems

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Oswald Reeves
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1 Module 7 Defining Coordinate Systems Introduction Objectives Outline of Topics Covered The use of coordinate systems is very important in managing 3D spatial data including point clouds. In this module you will learn how to create and manage coordinate systems. At the end of this lesson, you will: Be able to geo-reference a point cloud or set of point clouds to an assumed coordinate system Understand the difference between each method of setting the coordinate system Know how to save the new coordinate system Section Description Page 1 Understanding Scan Coordinates and Coordinate Systems 2 2 Setting Coordinates using Vertical Points, and Azimuth 4 3 Setting Coordinates using 13 Database to Use Use the previously modified data base: Tryon Road.imp Units in Feet. Coordinate labels: X, Y, & Z Default As-Scanned Coordinates The default setting of the coordinate axes during scanning with the Cyrax 2500 is with the origin of the coordinate axis at a point within the scanner. The orientation of the axes is dependent upon the position of the scanner. The default position of a Cyrax scan cloud is with the Y coordinate up, the Z axis in the opposite direction of the scan, and the X axis pointing to the right of the scanner. Use the Right Hand Rule with the index finger pointed UP Page 1 of 20

2 1 Understanding Scan Coordinates and Coordinate Systems General Discussion There are certain situations in 3D laser scanning where a full Registration for the purposes of geo-referencing is not necessary based on the deliverables required. For the registration process, a minimum of 3 points (within three axes - X,Y,Z) in the project must be known and scanned for the transformation (rotation and translation of the ScanWorlds) to work. Typically more than 3 points are used to allow for redundancy and reduction of errors. However, depending on the final deliverables, a full registration process may not be necessary. Examples of deliverables that might not require full Registration (for Geo-referencing) are: A 2D planimetric map (no topography or elevations) A 3D topographic map of a relatively small area (e.g. 200m X 200m) For these situations, Cyclone has the capability of setting the project coordinate system using a variety of methods described further in this document. These methods are listed below: Translation of existing coordinate system to user-defined reference point. Translation to new reference point, orientation measured by user entered azimuth Up direction set by vertical pair(s) of points, orientation by azimuth Up direction set by known elevation points (benchmarks), orientation by azimuth In each of these cases, the XYZ coordinate basis of the scanner is transformed into real world Cartesian coordinates that are either known (control) or assumed (defined by user). For each case, the minimum number of constraints is used to determine the new coordinate system, and there is little or no information to detect blunders. The user must be careful to use the best practices as described in this document to avoid misuse of these features. NOTE For 3D laser scanning surveys that require the data be georeferenced to an existing coordinate system, Cyra highly recommends that the standard Registration process be used with a redundant amount of control points. Page 2 of 20

3 When visualizing a single or registered point cloud as oriented in accordance with a world or conventional survey coordinates use the left hand rule. Cartesian coordinates [named after René Descartes], are a system for representing the relative positions of points in a plane or in space. In a three-dimensional space, a point is specified by three numbers (x,y, and z) representing the distances of the point from three intersecting straight lines (or planes), referred to as the x-axis and the y-axis and the z-axis. Each axis (or plane) is normal to the other two axes. Visualizing Cartesian Coordinates In the Cartesian coordinate system your thumb represents the +X axis, your index finger represents the +Y axis, and your middle finger represents the + Z axis. When Registered to Survey Coordinates use the Right hand Rule Visualizing Survey Coordinates In conventional survey coordinates your thumb represents Easting, your index finger represents North, and your middle finger represents Elevation. Page 3 of 20

Default Cyrax Point Cloud Coordinates for HDS 2500 Scanner Default Cyrax Point Cloud Coordinates for HDS 3000 Scanner 2 Setting Coordinates using Vertical Points, and Azimuth Using Twin- Target Pole

another point in the scan to establish the horizontal orientation from North.

4 Default Cyrax Point Cloud Coordinates for HDS 2500 Scanner Default Cyrax Point Cloud Coordinates for HDS 3000 Scanner 2 Setting Coordinates using Vertical Points, and Azimuth Using Twin- Target Pole Create New Project Folder Create New Registration In this lesson you will utilize a special Twin-Target Pole accessory (available from Cyra) to establish a vertical reference on the site, along with another point in the scan to establish the horizontal orientation from North. Since this method is based on a minimal number of constraints, it should only be used with a full understanding of the caveats and potential error sources. As with all surveying work, you should always include independent checks to verify the final solution. We will create a project with only two ScanWorlds, ScanWorld 1 and ScanWorld 7. Under the database Tryon Road.imp create a new Project Folder and re-name it to Coordinate Setting. (Create Project) Under the new Project folder named Coordinate Setting create a new Registration. (Create Registration) Rename it to Reg of SWs 1&7. Page 4 of 20

5 Set ScanWorld 7 to Home Register ONLY ScanWorlds 1 & 7 together using the existing target tie points. (Hint: Use the Add Auto Constraints function). Note how these two point clouds have been scanned from opposite sides of the bridge. Note that the default coordinate system of each ScanWorld is: Y Up; Z Opposite to scan direction; X to the right of the scanner. Set ScanWorld 7 as the Home ScanWorld Register the two ScanWorlds by clicking Registration Register. Reduce constraint weight of tie point T1 to 0.1. Re-register the ScanWorlds Register ScanWorlds 1 & 7 Create and open the new ModelSpace Figure 6-2 Create ScanWorld and Freeze Registration. Close Reg window. Then open a ModelSpace View for ScanWorld Registration SW1&7. See Figure 6-3. Rename the new ModelSpace and the new ModelSpace View to ModelSpace Reg 1&7. See Figure 6-4. Double-click on the ModelSpace view ModelSpace Reg 1&7 to open it. Page 5 of 20

Create new ModelSpace and ModelSpace Views Review the coordinate system Figure 6-3 Default ModelSpace Names Figure 6-4 ModelSpaces renamed Note the location

The origin is in its default position the scan head for ScanWorld 7 since this was set as the Home ScanWorld during registration.

6 Create new ModelSpace and ModelSpace Views Review the coordinate system Figure 6-3 Default ModelSpace Names Figure 6-4 ModelSpaces renamed Note the location of the origin and the general directions of the axes. The origin is in its default position the scan head for ScanWorld 7 since this was set as the Home ScanWorld during registration. The axes are aligned to how the scan head was oriented in ScanWorld 7. Click on any point and look in the lower part of the screen to view the coordinate. Notice that it is still in the Scanner coordinate system. Figure 6-4 The registered scan in its default coordinate system. Page 6 of 20

Set New Coordinate System Select points for setting coordinate system Turn on Tie Point Annotations Figure 6-5 Orthographic Plan View Now we are going to Set a New Coordinate System.

7 View ScanCloud from Above Rotate the view to look down on the scan from above. The view locks in the current coordinate systems top viewpoint. This is not a true top viewpoint according to the real world coordinate system, but rather a top view based on the orientation of the home scanner when the scan was made. Set New Coordinate System Select points for setting coordinate system Turn on Tie Point Annotations Figure 6-5 Orthographic Plan View Now we are going to Set a New Coordinate System. Using the targets shown in the ModelSpace, a new coordinate system can be created by selecting the points that will determine the origin, rotation, and translation of the new system. Zoom into the twin target pole assembly, located in the right side of ScanWorld 7. The top and bottom tie-points have been modeled (2 vertices) Select all vertices in the new registered ScanWorld by going to Set Selectables [Shift s] Check Vertex Click on Select Go to Tools Annotations Add/Edit Annotations Check the box to make the Target ID labels visible Close window Page 7 of 20

8 Turn on the Target ID Annotations Figure 6-6 Page 8 of 20

Select Vertices of Twin Target Pole Assembly Figure 6-7 Twin target pole assembly viewed in ModelSpace See above three illustrations of the components of the Twin Target Pole Assembly The twin target

Select the vertex on the bottom (lower) target of the pole (t6l). Make sure that only the vertex is selected, and not a point in the point cloud.

9 Select Vertices of Twin Target Pole Assembly Figure 6-7 Twin target pole assembly viewed in ModelSpace See above three illustrations of the components of the Twin Target Pole Assembly The twin target pole, even though set vertical in the field, may not look upright in the scan. This is because the scanner was not oriented to the vertical axis as determined by gravity. Select the vertex on the bottom (lower) target of the pole (t6l). Make sure that only the vertex is selected, and not a point in the point cloud. You can look at the status bar on the bottom of the screen to verify that you have selected a vertex. To make picking the line easier, either turn off the pickability of point clouds in the Set Selectable dialog, or zoom in closer to the vertex. Figure 6-8 Tie point t6l is selected Page 9 of 20

Select Top Tie Point Zoom back out and multi-select the vertex at the top target of the pole. To multi-select, hold down the Shift key when picking the vertex or use the multi-pick mode.

10 Select Top Tie Point Zoom back out and multi-select the vertex at the top target of the pole. To multi-select, hold down the Shift key when picking the vertex or use the multi-pick mode. Select the azimuth point to determine horizontal orientation Now you have two points selected (the top and bottom of the twin target pole). These will be used to set the up direction for the new coordinate system. Now all we need is another point in the scan(s) that establishes an azimuth direction from tie point T6l with respect to North (or South) depending on your hemisphere. Select a third vertex (T4) to be used to set the orientation or rotation of the system to the North direction. In this case, we have measured the azimuth from the first point (with the twin target pole) to the target T4 on the bridge railing by using a compass. Don t forget to multi-select, as you want to keep the original two picks on the twin target pole. Figure 6-9 Select the azimuth point Page 10 of 20

11 Change Coordinate Axes Labels Change Coordinate Labels from X,Y,Z to N, E, & El. Set New Coordinate System From Points Figure 6-10 From the View menu, click on Coordinate System Set From Points... to display the Set Coordinate System From Pick Points dialog. Figure 8-11 Page 11 of 20

12 Enter Values in Set Coordinates from Pick Points Window The Dialog Box should Look Like This => Now that the picks have been made, you need to indicate which pick points will be used to set up the coordinate system; and what values to use for the origin coordinate and the azimuth. Notice that Cyclone automatically numbers the points in the order that they were picked. (The color of the letters is maaggeennt taa) In this example, points 1&2 are the bottom and top points of the twin target pole, and point 3 is the azimuth point T4. Enter the following values in the Dialog box: Reference Point = 1 (the bottom target on the twin target pole) Easting = ft (assumed) Northing = ft (assumed) Elevation = (assumed ground = ) Azimuth Point = 3 (the target on the bridge railing) Angle = 295 deg <N 65 E> (measured by compass) Top Point = 2 Bottom Point = 1 Figure8-12 Fill in the fields as shown above. Page 12 of 20

13 Once the coordinate data is entered, select OK. The coordinate system is now set for this ModelSpace using the coordinate information you provided. You can now check the coordinate values for other known points in the site plan below. You have now successfully geo-referenced the point cloud! Figure 6-13 Compare your results to the control coordinates in the sketch above 3 Setting Coordinates using Instead of relying on the twin-target pole to establish vertical, this exercise utilizes known benchmarks to establish a vertical reference on the site and also uses an additional point in the scan to establish the horizontal orientation from North. Since this method is based on a minimal number of constraints, it should only be used with a full understanding of the caveats and potential error sources. As with all surveying work, you should always include independent checks to verify the final solution. As done in the previous exercise we will again use two of the ScanWorlds from the last exercise to complete this exercise. Page 13 of 20

From the Cyclone Navigator window click on the ModelSpace folder then click on Create ModelSpace or Right-Click on the ModelSpace folder and go to Create

14 Open a new ModelSpace in the ScanWorld You are now to create a second new ModelSpace using ScanWorld 1 and ScanWorld 7. Do the following operations: Create and open a new ModelSpace in the same ScanWorld. From the Cyclone Navigator window click on the ModelSpace folder then click on Create ModelSpace or Right-Click on the ModelSpace folder and go to Create ModelSpace. Rename the ModelSpace to ModelSpace Reg 1&7B Create and open a ModelSpace View. Notice that the new ModelSpace is still in the Scanner Coordinate System Figure 6-13 Create and Open a New ModelSpace Figure 6-14 New ModelSpace View Page 14 of 20

Select points for setting coordinate system Show all Tie Point Labels Select vertices This time we will select 5 points in the scan: The top/bottom targets on the twin-target pole The target to

15 Select points for setting coordinate system Show all Tie Point Labels Select vertices This time we will select 5 points in the scan: The top/bottom targets on the twin-target pole The target to determine azimuth (T4) Two targets set over known benchmarks (CL & D) in that order Select all tie points and turn on the annotations for each tie point to show the target ID s. Select the vertex on the bottom (lower) target of the pole Make sure that only the vertex is selected, and not a point in the point cloud. You can look at the status bar on the bottom of the screen to verify that you have selected a vertex. Select the azimuth point to determine horizontal orientation Figure 6-14 Twin target pole viewed in ModelSpace Select the top vertex of the Twin Target Pole while holding down the Shift key or using the multi-pick mode. Now you have two points selected (the top and bottom of the twin target pole). This will NOT be used to mathematically set the up direction for the new coordinate system; however, they are needed to determine a unique solution for the new coordinate system. NOTE: Although it is recommended to use the twin-target pole for this method, any pair of points that represent a general vertical direction can be used for this method, for example a plumb bob and string. Page 15 of 20

16 Multi-select the tie point T4 to be used to set the orientation or rotation of the system to the North direction. Figure 6-15 Select the benchmark points Select two benchmark points, shown as Point CL & T1 in the Site Plan. These selections, in addition to the elevation of the reference point, will be used to establish vertical in your new coordinate system. The elevation of the vertices has already been computed up from the ground benchmark by applying a target height constant. Select the Points in this order: 1. Bottom of Twin Target Pole T6l 2. Top of Twin Target Pole T6u 3. Tie Point T4 4. Tie Point CL 5. Tie Point T1 Set From Points From the View menu, click Coordinate System Set From Points... to display the Set Coordinate System From Pick Points dialog. Page 16 of 20

17 Figure 6-16 We are almost finished. Now that the picks have been made, we need to tell Cyclone which ones will be used to set up the coordinate system; and what values to use for the origin coordinate, benchmarks and azimuth. Information to be entered Enter the following values in the Dialog box: Refer to Figures 9-16 and Reference Point = 1 (the bottom target on the twin target pole) Easting = ft Northing = ft Elevation = ft Azimuth Point = 3 (the tie point T4) Angle = 295 deg <N 65 E> (measured by compass) Top Point = 2 Bottom Point = 1 Elevation Point 1 = 4 (Tie Point CL1 on sketch) Elevation = m Elevation Point 2 = 5 (Tie Point T1 on sketch) Elevation = m Page 17 of 20

18 Enter Data into Fields Designations of Tie Points Figure 6-16 Correct Data Entered into Fields Figure 6-17 Page 18 of 20

Technical Notes Save the new coordinate system Once the coordinate data is entered, select OK. The coordinate system is now set for this ModelSpace using the coordinate information you provided.

19 Technical Notes Save the new coordinate system Once the coordinate data is entered, select OK. The coordinate system is now set for this ModelSpace using the coordinate information you provided. The vertical accuracy of resulting data points using this method is dependent on the accuracy of the benchmarks used and the accuracy of scanning the benchmarks It is recommended that 3 or 4 benchmarks be used as a check on the final solution. In addition, accuracy is also a function of the geometry of the benchmark points used with respect to the reference point. Ideally, the benchmark points should be at the extents of the project and should have a wide aspect ratio with respect to the reference point. For example, using points along the same line will result in poor elevation accuracy as you move away from the line. When you set the coordinate system using the procedures above, you are only setting it for that individual ModelSpace. If you would like to keep this coordinate system and set it as the default coordinate system for its parent ScanWorld, follow the procedure below: Set the New Coordinate System for Parent ScanWorld From the View menu, click Coordinate System Set ScanWorld Coordinate System A warning message will appear asking if you want to set the coordinate system for this ModelSpace s parent ScanWorld, select Yes You can see the results when you open a new ModelSpace in the same ScanWorld. Figure 6-18 Setting the new coordinate system for ScanWorld Page 19 of 20

Saving Other Coordinate Systems Using multiple user-defined coordinate systems can be very helpful in the navigation and analysis of large ModelSpaces.

To save the current coordinate system 1 From the View menu, point to Coordinate System, and then select Save Edit Coordinate Systems.

20 Saving Other Coordinate Systems Using multiple user-defined coordinate systems can be very helpful in the navigation and analysis of large ModelSpaces. The User Coordinate Systems dialog is used to save, restore, and delete user-defined coordinate systems. To save the current coordinate system 1 From the View menu, point to Coordinate System, and then select Save Edit Coordinate Systems... to display the User Coordinate Systems dialog. 2 Click the Save icon. The Coordinate System Name dialog appears. Figure Enter a name for the current coordinate system, and then click OK. The current coordinate system is saved. Figure 6-20 End of Training Module 7 Page 20 of 20

Cyclone Tips and Tricks. Hexagon Geosystems Track June 2012

Cyclone Tips and Tricks. Hexagon Geosystems Track June 2012 Cyclone Tips and Tricks Hexagon Geosystems Track June 2012 Built-in Hotkeys Enhanced Working Format Open GL Modes There are some very powerful built-in viewing hotkeys in Cyclone. Here are some of them: