Define Projection

Function Description: Define a coordinate reference system for point cloud data. The coordinate reference system generally includes geographic coordinates (usually latitude and longitude coordinates), geocentric coordinates and projected coordinates (plane coordinates converted by projection). This feature only supports defining geographic and projected coordinates.

Steps

1.Click the Define Projection button to bring up the Define Projection pop-up box.

OpenPointCloud

Description:

  • Select Input file: The input file can be a single point cloud data file or multiple point cloud data files. File format: *.LiData.

  • Target Coordinate System Name: Displays the name of the currently set coordinate system and supports custom setting of the coordinate system name.

  • Detail: Displays detailed information about the currently set coordinate system.

  • Add Coordinate System(Add): Users can add external coordinate system settings or customize coordinate system settings. LiDAR360MLS software provides three ways to add external coordinate system:

    • Add Geographic Coordinate System
    • Add Projected Coordinate System
    • Add Vertical Coordinate System

  • Filter: Users need to enter a customized coordinate system. By entering the coordinate system keywords, the corresponding coordinate system can be filtered from the Coordinate reference systems of the world table (for example: to set the point cloud coordinate system to WGS 84 / UTM Zone 49N, users can enter UTM 49N in the filter for fast screening, or enter its EPSG number 32649 for quick search.) Users can also import external coordinate system by clicking the Add Coordinate System button.

  • Set Coordinate System: Select the coordinate system to be set, either from the default coordinate system or a custom coordinate system. Firstly, you can select the horizontal coordinate system in the Horizontal tab, and then the vertical coordinate system will be ellipsoid height by default. If you need to define a vertical coordinate system, you can switch to the Vertical tab to select a vertical coordinate system, and the two together form a combined coordinate system. The coordinate system selection interface contains the following nodes:

    • Recent: Records the recently used coordinate system.
    • Favourites: Coordinate system for adding collections.
    • Projected Coordinate Systems: All default projected coordinate systems are included.
    • Geographic Coordinate Systems: All default geographic coordinate systems are included.
    • User Defined Coordinate Systems: All custom coordinate systems are included.
    • Vertical Coordinate Systems: All default vertical coordinate systems are included.
    • User Defined Vertical Coordinate Systems: All custom vertical coordinate systems are included.

    Right-click on any coordinate system, select the Favourites function from the pop-up menu, and the selected coordinate system will be added to bookmarks. Right-click on a bookmarked coordinate system, select the Remove from Favourites function, and the coordinate system will be removed from bookmarks.

    Right-click on any custom coordinate system, select the Delete function, to delete the custom coordinate system. If the deleted custom vertical coordinate system is being used in a custom composite coordinate system, it will prompt whether to delete the composite coordinate system simultaneously. Choosing "Yes" will delete all these coordinate systems, while choosing "No" will not proceed with the deletion operation.

    Right-click on any coordinate system, select the Copy and Modify function to modify the coordinate system parameters and save it as a custom coordinate system. The parameters of the currently selected coordinate system will be filled into the corresponding modification interface. For specific settings, refer to the "Adding Coordinate Systems" section on this page.

  • Set Geoid Model: On the Vertical tab page, the user can set the geoid model of the vertical coordinate system. If the user need to use this option, the user need to provide the vertical reference grid data. For the method, please refer to the next section Vertical Coordinate System. At present, this setting has the following three situations.

    • When this option is not set, if the vertical datum grid data is provided, the appropriate geoid model will be automatically searched and used during coordinate transformation. If not provided, the geoid model will not be used during coordinate transformation (except for the EGM2008 model included in the software installation package).
    • If the selected vertical coordinate system can use the geoid model supported by default, it can be selected from the drop-down list, and the model will be specified when performing coordinate transformation. For the geoid models currently supported by default in LiDAR360MLS software, please refer to the Geoid Model page.
    • If the geoid model to be used is not included in the package provided by PROJ, the user can place the model file to be used under the geoid folder in the software installation directory, and then add the geoid model by clicking the Add Geoid button to add the file (support tiff and gtx formats), the model will be added to the drop-down list, after selecting the added model, the custom geoid model will be used in the coordinate transformation process.

      If the coordinate range of the selected geoid model does not match the coordinate range after point cloud coordinate transformation, the model will not take effect.

  • Selected Coordinate System: The information of the coordinate system selected by the user will be displayed here.

  • After clicking OK, the WKT information representing the projection will be written to LiData.

Vertical Coordinate System: Users can customize the vertical coordinate system. Vertical coordinate system transformations and grid projections require vertical datum grid data for valid transformations. EGM2008 geoid model elevation conversion is provided by default in the software. If you need to support other regional geoid models, you need to download the corresponding grid data files. The grid files are provided by the official PROJ library, which can be downloaded here proj-data-1.8, or on the official website https ://proj.org/download.html to download the latest version of proj-data. After downloading, unzip the file to the geoid folder in the software installation directory, the default is C:\Program Files\GreenValley Suite\LiDAR360MLS\7.2.0.0\geoid, "7.2.0.0" is the version number, and there will be differences between different versions.

Note: The custom geoid model must be placed in the geoid folder to take effect.

Add Geographic Coordinate System

OpenPointCloud
  • Name: Users can customize the name of a geographic coordinate system.
  • Datum:
    • Name: Users can customize a datum name or select a known datum from the drop-down list.
    • Spheroid: If a user selects the datum from the drop-down list, the ellipsoid parameter does not require to be entered.
      • Name: The name of the spheroid.
      • Semimajor Axis: Spheroid's major semiaxes.
      • Inverse Flattening: Inverse flattening of the spheroid.
  • Angular Unit:
    • Name: Users can customize the angle unit name, or select the angle unit name from the drop-down list.
    • Radians Per Unit: Define the unit of arc in the geographic coordinate system.
  • Prime Meridian:
    • Name: Users can customize the name of the central meridian, or select the name of the central meridian from the drop-down list.
    • Longitude: Enter the central meridian longitude.

Add Projected Coordinate System

OpenPointCloud
  • Name: Users can customize the name of a projection coordinate system.
  • Projection:
    • Name: Users can customize a projection name or select a known projection from the drop-down list. It should be noted that user-defined projections can be modified from a projection template selected from the drop-down list.
  • Linear Unit:
    • Name: Users can customize the linear unit name or select the linear unit name from the drop-down list.
    • Meters per Unit: Input meters per unit.
  • Geographic Coordinate System: User can click Modify to select a geographic coordinate system.
    • Change: When the user clicks the Change button, the following dialog box will pop up to modify the geographic coordinate system. Users can filter out the desired coordinate system through the Filter operation. Supports selection of default geographic coordinate system and custom geographic coordinate system.
OpenPointCloud

Add Vertical Coordinate System

  • Name: Users can customize the name of a vertical coordinate system.
  • Direction: Sets whether the direction of the axis is up or down.
  • Datum Type: Sets the datum type of the vertical coordinate system. Ellipsoidal is an ellipsoidal datum and Gravity-related is a gravity field datum.
  • Datum: This option allows you to set the ellipsoid datum when the datum type is set to Ellipsoidal. When selected, the ellipsoid parameters will be automatically populated in the ellipsoid parameter list below.
  • Vertical Datum: This option allows you to set the vertical datum when the datum type is set to Gravity-related.
  • Spheroid: If a user selects the datum from the drop-down list, the ellipsoid parameter does not require to be entered.
    • Name: The name of the spheroid.
    • Semimajor Axis: Spheroid's major semiaxes.
    • Inverse Flattening: Inverse flattening of the spheroid.
  • Linear Unit:
    • Name: Users can customize the linear unit name or select the linear unit name from the drop-down list.
    • Meters per Unit: Input meters per unit.
  • Default: Restore default parameters.

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