On Grid: Tools and Techniques to Place Reality Data in a Geographic Coordinate System

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1 RC21940 On Grid: Tools and Techniques to Place Reality Data in a Geographic Coordinate System Seth Koterba Principal Engineer ReCap Autodesk Ramesh Sridharan Principal Research Engineer Infraworks Autodesk Learning Objectives Discover the tools and workflows in ReCap 360 desktop and web to get reality data into the desired coordinate system. Gain awareness of common pitfalls in working with geographic reality data Learn how to import and process geographically oriented reality data in Infraworks 360 and Civil 3D Catch up on the most effective end-to-end workflows for geographic reality data Description For many architects, engineers, planners, and project managers the full value of reality data is not unlocked until it is placed and oriented in the right context. If you use reality data and need to place that data in a specific geographic coordinate system, this instructional demo is for you. We will illustrate the tools and techniques that you will need to snap your data into the position and orientation that your project needs. Seth Koterba will start the demonstration by showing a variety of tools and workflows in ReCap 360 Pro software that get your project started off right. Then Ramesh Sridharan will illustrate how to bring this data into InfraWorks 360 and Civil 3D to visualize and process it in context; extracting the most out of your data. We will focus on several reality data types from static terrestrial scans to dynamic mobile scans and even aerial photo-reconstruction projects. We ll get you prepared to take your data where it was meant to go. This session features ReCap 360, InfraWorks 360 and Civil 3D. Your AU Expert(s) Seth Koterba is a Principal Engineer in the Product Development Group (PDG) working on the ReCap product line. Seth joined Autodesk in 2012 after the acquisition of small startup company, Allpoint Systems, which he co-founded. His current responsibilities include product ownership of the core functionality, algorithms and technology used for the visualization and processing of laser scan data in ReCap 360 and other Autodesk products. In addition to overseeing development, he is also a programmer and directly contributes to the ReCap product line. Outside of his development responsibilities, he spends time interacting with customers and partners to understand their challenges and workflows which ultimately guide the Page 1

2 development of new technologies and features. Seth s education includes undergraduate degrees in Mathematics and Physics, as well as a Master s degree in Robotics from Carnegie Mellon University. You can reach Seth at Ramesh Sridharan has been working with reality capture point clouds, image processing, and machine learning based software development since With over 15 years of experience, he has successfully driven programs in research and development, technical sales, partner marketing, and customer analysis. He has experience working with customers to understand and set industry workflows which drive the technology forward. He is an expert in pushing technology to its limits and in converting research findings into products that users can apply to real life problems. He is a pioneer in the field of reality capture point cloud product development that can handle and extract information from a large number of 3D datasets. As a Principal Product Owner in the Product Development Group (PDG) since he joined Autodesk in 2014, Ramesh is responsible for information extraction from Reality Capture for AEC applications. Ramesh is a post graduate of Indian Institute of Technology with a research focus in Image Processing and Artificial Intelligence. You can reach Ramesh at Page 2

3 Data in Context Points Clouds are becoming increasingly vital for many real world projects, especially in the AEC market. Almost all infrastructure projects use reality capture data directly or indirectly to gather existing and as-built conditions. If you ve signed up for this course you may not need any convincing, but in nearly all of these applications, reality data provides more value when it is placed in context relative to other sources of data like satellite imagery, maps, elevation profiles, proposed designs, etc. This course is designed to help provide a complete picture of the tools and techniques currently available for reality capture data in the Autodesk ReCap product line and as well as downstream workflows for engineering and design applications like Infraworks and Civil 3D. In this section, we ll review the basics of coordinate systems and draw attention to the different types that are commonly used. Understanding Coordinate Systems Coordinate systems (CS) are a fundamental framework for any representation of 2D or 3D data, digital or analog. When working with geo-located data, coordinate systems gain even more importance as well as complexity. An important concept to understand is the difference between geographic and projected coordinate systems. A geographic coordinate system is one that allows every location on Earth to be defined by a set of coordinates. A geographic CS is typically a spherical system that uses horizontal and vertical lines to generate a grid [Figure 1]. Due to their lack of uniformity in distances between lines of longitude, especially around the poles, geographic CSs are not commonly used in design software. Instead, the surface of the Earth is often approximated as a plane around a small area of interest. These planar approximations are called projected coordinate systems and allow for specifying geographic locations in a Cartesian coordinate system [Figure 2]. FIGURE 1. GEOGRAPHIC COORDINATE SYSTEMS ARE SPHERICAL CSS THAT USES VERTICAL AND HORIZONTAL LINES TO DEFINE A GRID. Geographic Coordinate Systems WGS84 NAD83 TABLE 1. EXAMPLE COORDINATE SYSTEMS Projected Coordinate Systems US State Plane Universal Transverse Mercator (UTM) An alternative coordinate system that is commonly used is called Earth-centered Earth-fixed (ECEF). ECEF is both a geographic and Cartesian coordinate system. Its origin is at the center of the Earth and the z-axis is approximately along the axis of rotation while the xy-plane is approximately aligned with the equatorial plane. Page 3

4 FIGURE 2. A PROJECTED COORDINATE SYSTEM USES A PLANAR APPROXIMATION OF THE EARTH S SURFACE IN A LOCAL REGION. In the following sections we ll reference the different coordinate systems described above and point out tools and features that can be used for processing and visualization of reality data in these different CSs, as well as how to convert between them. Structured vs. Unstructured Data As another prerequisite, it s important to note that ReCap 360 Pro Desktop currently makes a distinction between two common types of point cloud data. Traditional tripod based terrestrial scans are referred to as structured data since each point is measured from the same origin and the data is ordered in a grid-like structure of rows and columns. Data that is not ordered in a grid-like pattern with a common origin is referred to as unstructured data. Examples include data collected using mobile platforms like aerial or vehicle mounted lidar, point clouds generated from photos or handheld scanners, and collections of structured data that have been unified into a single large point cloud. The structured vs unstructured distinction is an important one in the current evolution of ReCap 360 Pro and will be referenced frequently throughout this document. Survey Data When reality data is captured, it may be collected without the accurate location information necessary to place it in a geographic or projected coordinate system. The most common technique for adding this location information to the data is through the use of survey targets. These are easily identifiable objects that can be assigned specific coordinates during or after the collection process. Typically these are checkerboards or spheres; several examples are shown in Figure 3. A surveyor can identify these objects outside of the capture process and determine their coordinates in a specific coordinate system. Page 4

5 FIGURE 3. SURVEY TARGET EXAMPLES Survey Data in ReCap 360 Pro Desktop In ReCap 360 Pro Desktop, targets are extracted and identified during or after the registration process for structured data only. ReCap supports checkerboards, spheres or manual survey markers. These survey points are created in registration mode by first selecting the target type (see Figure 4) and then clicking in the area of the target. If the target is a checkerboard or sphere, its location will be automatically extracted. For manual targets, the user must select the precise location of the target. Once a target is created, it can be designated as a survey point by selecting the make survey point option. If survey data is available in a text format, it can be imported in the drop down dialog for setting or selecting the target s name. It is import to note that ReCap only supports working in Cartesian coordinate systems, so survey data must be provided in a projected CS or ECEF. FIGURE 4. TARGET CREATION AND SURVEY MARKERS IN RECAP 360 PRO DESKTOP. Tips: In ReCap and lower versions, use meters for setting the survey coordinates. Check the targets report to inspect error per scan and per target to identify potential mistakes, bad targets, typos, etc. If you use targets for registration, you ll need at least 3 targets in each scan. Otherwise cloud-to-cloud registration will be used for the entire project. For applying survey alignment, 3 per scan is not required. Survey Data in ReCap 360 Web Page 5

6 In the ReCap 360 Photo-to-3D service, survey data is added during the initial registration process. After importing photos, select survey settings and when adding a registration point, click the eyedropper symbol to open the survey point dialog. FIGURE 5. IN RECAP 360 PHOTO-TO-3D CHOOSE THE SURVEY SETTINGS TO ADD SURVEY POINTS The Photo-to-3D service supports survey points specified in three different coordinate system types: 1) any projected CS using the XYZ option, 2) geographical CS (WGS84) using the LLA option, and 3) ECEF. Tips: For each registration point, you ll need to find the same point in other photos. Select at least 4 views of the same point for best results; more is better. Fewer well placed and accurately selected registration points is often better than lots of them. Think 4-6, not dozens. Currently photo-to-3d service tends to give better results when specifying the coordinates in metric units as opposed to imperial units. If you have imperial units, it is recommended that you convert to metric units before entering the survey coordinates. You can paste a comma delimited x,y,z string into the x-field and all three values will be set at once. Photos without survey points If survey data was not collected for a photo project, but the photos were tagged with geolocation data from a GPS device (EXIF metadata), the project will be geo-located automatically. Nadir optimization For photo projects that are collected with a camera angle perpendicular or nearly perpendicular to the ground, turning on nadir optimization option can help improve the quality of the resulting reconstruction. Note that this option is not required to geo-locate the data. Page 6

7 FIGURE 6. NADIR OPTIMIZATION FOR PHOTO PROJECTS WITHOUT SURVEY DATA Coordinate Systems for Unstructured Data The most common raw format for laser data collected using mobile platforms like aerial or vehicle mounted lidar is LAS or LAZ. These formats include metadata for specifying geographical coordinate systems. When importing these formats into ReCap 360 Desktop the advanced settings screen can be used to configure the coordinate systems. There are two fields that need to be set under the coordinate system section: current and target [Figure 7]. The current CS defines the CS that the raw data is currently in. If the raw data file contains CS metadata, the current field will be set automatically. The target CS defines the CS that the user would like the data to be in when working with it in ReCap and/or other products. For each field, a drop down menu gives you the choice of hundreds of different CSs. If the auto-detected CS is inaccurate, it can be changed and overridden. In many cases, these fields will be set to be the same, but in certain situations a conversion may be necessary. Some examples are when raw data is in a different CS than the user prefers to work (e.g. UTM instead of state plane), when a units conversion is desired such as the raw data being in feet, but the user prefers meters, or when the raw data file s metadata is incorrect. FIGURE 7. ADVANCED SCAN SETTINGS IN RECAP 360 DESKTOP Tips: The coordinate system cannot be changed after import. Make sure to set this information correctly up front, or start from the beginning and re-import. Page 7

8 The general settings tab shows what the current coordinate system is and even allows you to attempt to change it. Warning: This dialog is broken and should not be used. It will be updated or removed in the future. Workflows In this section, we ll highlight several workflows from raw data to import in Infraworks 360. Each workflow will address combinations of data with and without survey points, including photo projects, as well as both structured and unstructured laser data. These exact workflows or combinations of them will address most workflows that you will encounter. Scenario 1: Photo project with survey points and structured data with survey points ReCap 360 Web In this scenario, the photo project should be processed using the survey points process defined above using the XYZ survey option. Use a metric CS for best results. The output options should include the RCS format for a point cloud result to be imported in Infraworks 360. ReCap 360 Pro Desktop The laser data should be imported in ReCap 360. In the import screen, choose the advanced tab. Here you ll need to enter both the current and target CS as the CS that the survey data is in. If this step is not done, you ll need to enter this info in Infraworks 360 later. If the data is not registered, you ll need to register the scans using ReCap 360 Pro s registration tools. After indexing, you can return to the registration screen and apply the survey data as described above. Current versions of ReCap 360 Pro, have a bug when entering survey data in imperial units, so be sure to convert to metric units if necessary. Check the residual errors to verify that the survey data was applied as expected. Finally, if desired, you can export to a unified RCP/RCS. Infraworks 360 At this point you should have an RCS for the photo project and an RCP/RCS for the laser data. After creating a new project in Infraworks 360 you ll need to add a new data source. 1. Click 2. On the Data Sources panel, do the following: a. Click (Add File Data Source). b. Click Point Cloud and choose the photo RCS 3. Configure the data source. a. Double click the data source or right click and choose configure in the context menu Page 8

9 b. In the Coordinate System field, choose the CS of the survey data used in the photo processing. E.g.: c. Choose Close & Refresh 4. Now add the laser project data a. Repeat steps 1 and 2 b. Choose the unified RCP or the original RCP (unified is recommended) 5. If the CS was set in ReCap during the import process, the point cloud should already be configured. If this part was missed during import in ReCap, you ll need to repeat step 3 for this data. Scenario 2: Photo project without survey points ReCap 360 Web In this scenario, the photo project will need to have GPS data for geo-location purposes, but otherwise should be processed normally. Correspondences between key features can be added if necessary, but no survey data needs to be added. Remember to use the nadir option if the photos are taken from a high angle relative to the ground. After the photo project is complete, download the RCS file and you ll also need to navigate to the A360 folder and download the RCP file (more on this below). Infraworks 360 At this point you should have an RCS for the photo project. After creating a new project in Infraworks you ll need to add a new data source. 1. Click Page 9

10 2. On the Data Sources panel, do the following: a. Click (Add File Data Source). b. Click Point Cloud and choose the photo RCS 3. Extract the local offset from the photo RCP file a. The photo RCP downloaded from the A360 project is a different format than the desktop RCP used for laser scans. It is in XML format and can be opened with a text editor. b. Search for the section of the file that looks like the following: <EXPORT> <GIS datum="wgs84" lat=" " lon=" " alt="0" csys="enu"/> </EXPORT> 4. Configure the data source. a. Double click the data source or right click and choose configure in the context menu b. In the Coordinate System field, choose the XY-M option for the Coordinate System and under the Position section, you ll need to enter the local offset for the data collected in step 3. Enter the Lon value in the X field, Lat in the Y field and 0 in the Z field. c. Choose Close & Refresh Scenario 3: Photo project without survey points and laser project with survey points. ReCap 360 Web In this scenario, the photo project is not required to have GPS data for geolocation purposes, and can be processed normally. Correspondences between Page 10

11 key features can be added if necessary. After the photo project is complete, download the RCS file ReCap 360 Pro Desktop The point cloud data should be imported in ReCap 360 Pro. Use the registration tools to create a cloud-to-cloud registration of the structured data. Next, import the RCS point cloud downloaded from the web application. In version 3.1, ReCap 360 Pro added a new feature for registering unstructured data to structured data (see Figure 8). This feature will allow you to tie the photo RCS into the registered structured data. After indexing, you can return to the registration screen and apply the survey data as described above. Current versions of ReCap 360 Pro, have a bug when entering survey data in imperial units, so be sure to convert to metric units if necessary. Check the residual errors to verify that the survey data was applied as expected. Finally, if desired, you can export to a unified RCP/RCS. FIGURE 8. UNSTRUCTURED REGISTRATION IN RECAP 360 PRO, DESKTOP VERSION 3.1+ Infraworks Click 2. On the Data Sources panel, do the following: a. Click (Add File Data Source). Page 11

12 b. Click Point Cloud and choose the unified RCP generated from ReCap 360 Pro 3. Configure the data source. a. Double click the data source or right click and choose configure in the context menu b. In the Coordinate System field, choose the CS of the survey data used. E.g.: c. Choose Close & Refresh Scenario 4: Unstructured LAS/LAZ data ReCap 360 Pro Desktop Note: ReCap adds support for LAZ files and formal support for the ECEF coordinate system. Import the raw data and select the advanced tab. Choose the appropriate current and target CS for your data. In many cases, the current and target CS are set to be the same, but there are many scenarios where they can and should be different. The table below gives a few examples of possible scenarios Current Target Description UTM10S (UTM zone 10S) CA83-III (California SP zone 3) The raw data was in UTM but the user prefers to work in stateplane. ECEF MI83-S (Michigan SP South) The raw data is in ECEF and user prefers to work in stateplane LL84 ECEF The raw data is in WGS84 and user prefers ECEF MI83-NF (Michigan SP North Ft) MI83-N (Michigan SP North M) The raw data is in survey feet and user prefers to work in meters Infraworks 360 If the coordinate system information is set correctly in ReCap 360, importing into Infraworks 360 will not require configuration. The CS will be automatically detected and applied. Processing Geographical Data in Infraworks 360 and Beyond Once geographical data is placed in context, the value of reality data has just begun to blossom. Engineering and design tools like Infraworks 360 provide the capability to further cultivate the value of your data. For example, the InfraWorks 360 Automatic Terrain Generation tool provides an intuitive point cloud processing experience and brings reality to the reality capture industry. Page 12

13 One of the challenges of downstream processing is the hefty files sizes and point counts of reality data. They can be extremely large and extracting terrain is difficult. Users have to go through the painful task of either removing noise (or non-ground) points manually, or extracting/digitizing breaklines to create a terrain (which is not as information rich as point cloud data). In either case, it is not easy to generate terrain with point clouds and then there is the additional process of triangulating a large number of points. The InfraWorks 360 Point Cloud Terrain generation tool takes care of these pain points by filtering noisy data to deliver thin (information rich) point clouds and extract terrain raster. These point clouds can then be used for design in Civil 3D to create triangulated terrain directly or enforce breaklines for more detail. With these thin point clouds, sharing and using point cloud data is no longer science fiction to the point cloud industry. The InfraWorks 360 Point Cloud Modeling tool, enables user to create 3D virtual worlds from reality capture data by intelligently replacing features in point clouds with models in real world. All the extracted information are stored in geo-located coordinates so that users can export lists of assets, terrain and other information in proper geo-coordinate systems maintaining the consistency and resolution meant for the intended project. These tools and others will be discussed in more detail in course TR18477-L: Using Large Point Clouds for Infrastructure Projects. However, these topics, techniques and tools will be highlighted in this course in less detail. As an additional source of reference, the handout for TR18477-L is provided as an addendum to this course. Page 13