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Build a Project with Lidar Data

Ayelet Rabinowitz
  • Updated

This tutorial outlines the complete workflow for creating professional grade output in PhotoMesh using Lidar data:

Data Included in Training Folder (MetaDuo_LiDAR_Project_Data)

This project’s photos and Lidar were collected using two Phase One cameras and a RIEGL Lidar sensor, all mounted on a Lead’Air mount. This data and everything else you need to create your mesh is included in the MetaDuo_LiDAR_Project_Data folder:

lidar1.png

  • Aol folder
    • Large aerotriangulation area polygon shapefile – Orlando_Skyline_Training_Large_AoI.shp
    • Small aerotriangulation area polygon shapefile – Orlando_Skyline_Training_Small_AoI.shp
  • GCP folder
    • Sampled_LeadAir_Training_cp.gcp
    • Unsampled_LeadAir_Training_cp.gcp
    • PDF with descriptions of the control points used
  • Images folder
    • 454 photo files
    • XML file with the photo information – Orlando_MetaDuo_PhotoMesh_Import.xml
  • LAS folder
    • 9 LAS files
  • Water_Polygon folder
    • Water polygon file – Orlando_Training_Water_Polygon.shp

Download project data (83 GB)

Step 1: Starting a New PhotoMesh Project

  1. Click Start > Skyline PhotoMesh > PhotoMesh.
  2. Click the PhotoMesh button , and then click New (CTRL+N). The New Project dialog box is displayed.
    lidar2.png
  3. Enter a name and path location for your project.

Step 2: Loading the Project Photos and Lidar

Photos can be loaded into a project using several different methods. In this tutorial, we will be loading an XML file with a list of photos, their file paths, and all photo and photo collection information. More about: Loading Photos into a Project >

Lidar data can be loaded into a PhotoMesh project and integrated with project photos to supplement project data and increase model accuracy. PhotoMesh supports Lidar data in .las, .laz or .e57 formats. More about: Loading Lidar Data >

To load photos and Lidar:

  1. Load Photos: On the PhotoMesh Home tab, from the Photos dropdown menu, select Load from List. Then browse to the XML file with all the photo information (.\MetaDuo_LiDAR_Project_Data\Images\Orlando_MetaDuo_PhotoMesh_Import.xml). The photo files are loaded into the project.
    lidar3.png
  2. Load Lidar: On the Home tab, click the arrow under Lidar, and select Load Folder. Then browse to the LAS folder (.\MetaDuo_LiDAR_Project_Data\LAS), and click Open. All the Lidar files in the folder are loaded into the project.
  3. In the Project Tree, select the Lidars group, and in the Lidars list, select the check boxes of all the Lidars. Then click Select clickselect.png to set a different coordinate system. The Coordinate System dialog is displayed.
    lidar4.png
    lidar5.png
  1. In the Vertical Datum section, select Clear next to the Vertical Datum. Then click OK.
  2. Show a Lidar on the terrain to see if it fits with the project's photos, other Lidar, ground control points, etc. Proper alignment of the project’s photos with the Lidar data can be verified and corrected using ground control points by projecting the photos on the Lidars.
    In the Project Tree select the Lidars group, and then in the Lidars list, select all the Lidars. Then right-click > Show Point Cloud. Note that the point cloud may take some time to display.

lidar6.png

Step 3: Setting the Aerotriangulation Area

The AT area defines the area of the project on which PhotoMesh should perform aerotriangulation. Aerotriangulation is the process for determining the correct position and orientation of each of the project photos, based on inputted photo information, ground control points and tie points. If a project’s photos do not have fully trusted camera positioning and orientation information, this process must be performed before generation of the 3D mesh model.

The AT area automatically defined by the photos' GPS tag includes all the project’s photos. If you want to restrict the AT area to only the photos within a specific area on the terrain, the specific area can be defined using an AT area polygon that you draw or import. This enables you to perform aerotriangulation on a small subset of the project to validate camera parameters and build settings and check the resulting AT and reconstruction tiles before building the full project. More about: Setting the AT Area >

Your training folder includes two aerotriangulation area shapefiles: a large one and a small one. In this step, we first perform aerotriangulation on a small subset of the project to validate parameters and settings, so we will use the small aerotriangulation polygon.

To set the aerotriangulation area:

  • On the Home tab, click the arrow under AT Area, and select Import. Then in the Import Aerotriangulation Area Polygon Layer dialog, browse to the shapefile with the required polygon (.\MetaDuo_LiDAR_Project_Data\Aol\Orlando_Skyline_Training_Small_AoI.shp), and click Open.

lidar7.png

lidar8.png

Step 4: Using Control Points to Improve AT Results

PhotoMesh provides three types of control points for improving your AT results: ground control points, check points, and tie points. In this training exercise, we will be working with ground control points. Ground control points improve the accuracy of the model’s position by associating real-world X, Y, Z coordinates (generally obtained through surveying or sampling methods) with corresponding locations (in pixels) in photos.

Control points can be created in PhotoMesh or imported in a gcp (text format) file with control point information. More about control points >

In this tutorial, you will be importing a gcp file which includes the locations on the terrain in which control points were created and the pixel coordinates for each sampled photo in which each control point was sampled.

To import ground control point data:

  • On the Home tab, click the arrow under Control Points and select Import. Then in the Import Control Point File dialog, browse to .\MetaDuo_LiDAR_Project_Data\GCP\Sampled_LeadAir_Training_cp.gcp in your training packet, and click Open.

Step 5: Performing an AT Only Build

For optimal AT results, it is recommended to initially perform only the aerotriangulation step (“AT Only”), and then review the results, to ensure a precise AT which includes all project’s photos that intersect with the AT area, before proceeding with the rest of the build. If the results of the AT Only were in fact satisfactory, you can continue with the rest of the build process.

If the results of the initial AT Only build were unsatisfactory, AT parameters or collection properties should be modified and/or control points added/edited based on the aerotriangulation result, and then the AT should be repeated. More about: Evaluating and Improving Your AT >. When repeating the aerotriangulation, PhotoMesh determines precisely which tiles and which specific AT sub-processes were affected by the modification of properties or control points, enabling a much lighter and faster AT process. This iterative process should be repeated until satisfactory AT results are achieved.

To perform an AT Only build:

  1. On the Home tab, click Build. The Build Parameters dialog box is displayed.lidar9.png
  2. On the Steps tab, select AT Only. Then click Select and Manage Presets. The Preset Manager is displayed.
    lidar10.png
  3. On the Select Presets tab, clear the Selected Presets list on the right side of the Preset Manager by selecting each preset and clicking Remove . On the left side of the Preset Manager is a list of available presets. Select the AT: More Aggressive Match preset (for datasets with multiple camera angles and positions), and then click Add to move it to the Selected Presets Do the same for the DataPrep: Set SMPT quality to JPEG 98% preset (for projects that are quality focused, this preset requires above average processing). Then click OK.
  4. In the Build Parameters dialog, on the AT tab, set Camera Position Accuracy to Reliable position and orientation (DGPS and INS) – PhotoMesh assigns a strong weight to inputted camera positioning. If the inputted camera positions are inaccurate or inconsistent with any provided control points, it may be advisable to use the Standard GPS option. This option is recommended for collections captured by professional systems with accurate positioning and orientation information (e.g., using DGPS and INS).
    lidar11.png
  5. Click Build. Then enter a build name and click Ok. The PhotoMesh Build Manager is displayed.
  6. Select the required fusers (see Step 6) and click Build.
  7.  

Step 6: Starting and Managing Fusers

PhotoMesh fusers are the worker components of PhotoMesh, which allow you to share the demanding processing requirements of the different build steps (photo preparation, AT, point cloud, mesh model, texture, 3DML/other outputs) between several computers on the same network. When beginning the build process, the PhotoMesh Build Manager application determines what build steps are required and assigns them to the different fusers. PhotoMesh Build Manager and PhotoMesh fusers use the working folder to communicate: to deposit and collect pending tasks, and share information about fuser availability, status and progress. Before beginning the build process, you should start the fusers that will be participating in the build and set their working folder. More about: Working with Fusers >

Step 7: Performing Full Build and Generating Outputs

After satisfactory AT results are achieved in an AT Only build, you are ready to perform the full build process and generate your required outputs.

To perform a full build:

  1. Set the aerotriangulation area to include all the project’s photos. See Step 3 for more information. This time, use the large polygon shapefile to set the area: (.\MetaDuo_LiDAR_Project_Data\Aol\Orlando_Skyline_Training_Large_AoI.shp)
    lidar12.png
  2. On the Home tab, in the Build group, click Build. The Build Parameters dialog box is displayed.
  3. On the Steps tab, click Complete Project.
  4. Click the Reconstruction tab to configure the reconstruction parameters. More about: Setting Build Parameters > The parameters should already be defined as required based on the presets selected in step 5. Set the Point Cloud Quality option to High 1/2 resolution.lidar13.png
  1. On the Output tab of the Build Parameters dialog, select the 3DML check box. Then click Build. Enter a build name in the New build description dialog, and click Ok. More about: Setting Output Formats >
    lidar14.png
  2. When the build is complete, it will be listed in the Project Tree. Check its box to display the final output.
    Note:  To open the project in TerraExplorer, right-click on the build folder in the Project Tree and select Open with TerraExplorer.

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