Reproject Dataset

Function Description

When projecting a single dataset, the resulting data from a vector dataset transformation can be saved as a new dataset or directly convert the source dataset's projection. After projecting raster, image, or model dataset, the resulting dataset must be saved as a new dataset.

Function Entry

  • Start tab -> Data Processing group -> Project -> Reproject Dataset.
  • Toolbox -> Data Management -> Projection Settings -> Reproject Dataset.
  • In the workspace manager, select the dataset to project, right-click context menu -> Properties. In the dataset attribute panel, click the Coordinate System item -> Project button.

Parameter Description

  • Source Dataset: Sets the dataset to be projected and its data source. The source coordinate system area displays detailed description information of the source dataset's coordinate system.
  • Conversion Method: Click the drop-down button next to the Conversion Method label. The drop-down menu lists more than ten reference system conversion methods provided by the system. Users can select an appropriate method. For a description of conversion methods, please refer to Reference System Conversion Method Description. For information on conversion methods and scope of application, please refer to Transformation Model.
Notes:

Supports coordinate transformation for planar coordinate system datasets, providing the four-parameter transformation method. Does not support conversion between planar coordinate system and geographic coordinate system.

  • Projection Transformation Parameters: Different conversion methods can be selected. Click the settings button to customize parameters in the Parameter Settings dialog box.

    When selecting a three-parameter conversion method, such as Geocentric Translation, Molodensky, or Molodensky Abridged, in the Parameter Settings dialog box, you need to set three translation parameters (ΔX, ΔY, ΔZ). This conversion is essentially a geocentric transformation, converting from the center of one datum (0,0,0) to the center of another datum (ΔX, ΔY, ΔZ). The three-parameter transformation is a linear translation transformation, with the unit in meters.

    When selecting a seven-parameter conversion method, such as Position Vector, Coordinate Frame, or Bursa-Wolf, in the Parameter Settings dialog box, you need to set seven parameters: three linear translation parameters (ΔX, ΔY, ΔZ), three rotation angle parameters around the axes (Rx, Ry, Rz), and a scale difference (S). Translation parameters are in meters; rotation parameters are in arc seconds; and scale difference is in parts per million (ppm).

    • Proportional Difference: Indicates the scale scaling from the original coordinate system to the new coordinate system. When converting between planar coordinate systems, a proportional difference must be set. Proportional difference = unit conversion from original coordinates to target coordinates * 1000000. For example, when converting from planar coordinate system (millimeters) to planar coordinate system (meters), the proportional difference parameter should be 1000.
    • Rotation Angle (X/Y/Z): Indicates the rotation angle around the X/Y/Z axis, in arc seconds, default value is 0.
    • Offset (X/Y/Z): Also called translation amount, indicates the offset along the X/Y/Z axis, in meters, default value is 0.
    • Origin Coordinates (X/Y/Z): Indicates the coordinate value of the rotation origin X/Y/Z, default value is 0.
    • Import/Export Projection Transformation Parameters File: Click the import button at the bottom of the Parameter Settings dialog box to import a projection transformation parameters file with the suffix *.ctp, thereby importing the parameter information saved in the file as the current projection parameters. Click the export button at the bottom of the Parameter Settings dialog box to export the currently set parameters in the dialog box to a specified path for later use by importing.
  • Result Save As: Sets the save name and the data source where the projected result dataset will be saved.
  • Target Coordinate System: Provides three setting methods, as described below. After setting the target projection, the "Target Coordinate System" area will display the details of the target projection.
    • Reset Coordinate System: Click the "Reset Coordinate System" button, select "More" from the drop-down menu, and set the target projection in the "Coordinate System Settings" dialog box. For specific operations of coordinate system settings, please refer to Projection Settings.
    • Copy Coordinate System: Click the "Copy Coordinate System" button to pop up the "Copy Coordinate System" dialog box. You can choose to copy from a data source or from a dataset:
      • From Data Source: Select the "From Data Source" radio button, click the combo box drop-down button, select a data source, and set that data source's coordinate system as the target coordinate system.
      • From Dataset: Select the "From Dataset" radio button, click the combo box drop-down button, select a dataset, and set that dataset's coordinate system as the target coordinate system.
    • Import Coordinate System: Click the "Import Coordinate System..." button. In the pop-up "Select" window, choose a projection info file and import it. Supports importing Shapefile projection info files (*.shp;*.prj), MapInfo Exchange Format (*.mif), MapInfo TAB Files (*.tab), image projection info files (*.tif;*.img;*.sit), and projection info files (*.xml).
  • Model Convert Vertex Option: Only available when the source data is a model dataset, used to avoid object position misalignment after coordinate transformation. When the model dataset contains instanced models (model sub-objects with share times greater than 1), and the conversion involves geographic coordinate system to projected coordinate system, it is recommended to keep this option checked.
Notes:
  • Any projection has projection distortion, so the transformation process between different projections is usually not completely reversible. Map data can be projected from its original projection to some other projection, but it may not always be possible to convert it back very accurately. Therefore, users should back up the original file before projecting. Also, the number of projection transformations should be minimized to ensure more accurate results.
  • Each projection is designed to reduce distortion for a given area on a given characteristic, so various projections have a certain scope of application. When performing projection transformation, transformation should be carried out as much as possible within similar coordinate system ranges; otherwise, the accuracy of the projection transformation result is difficult to guarantee. For example, transforming a Mercator projection world map to a Gauss projection will only ensure accuracy near the central meridian, causing huge distortion in areas far from the central meridian.
  • In practical work, which conversion method to adopt depends on the specific situation. For determining each parameter, either purchase authoritative measurement data or verify the correctness of the parameters through known control point coordinates in both coordinate systems.
  • After projecting text, the text height and angle will be converted accordingly. If such changes are not desired, you need to reset the text height and angle for the converted text.
  • After reprojecting the dataset, the tolerance of the resulting dataset will be updated according to the new projection.

Related Topics

Batch Reproject

Transform Coordinates

Calculate Transformation Model Parameters