Point Conversions - Inverse Calculation

The Point Conversion tool allows single-point calculations of numeric coordinates.

There are three different operation types that can be performed using a single point: Conversion, Forward, and Inverse. This page describes the Point Inverse Calculation.

Inverse Calculation

An Inverse Calculation computes the distance between two known coordinates on the same datum. The result may be calculated using Geodesic, Rhumb, or Grid methods. Both the source and destination points must be referenced to the same geodetic datum.

Note: For both Forward and Inverse conversions, when height values are entered, the distance is scaled to a height above the ellipsoid. This is also true for Geocentric coordinate systems that are 3 dimensional by nature. 3D Cartesian coordinates will be reduced to the surface of the datum.

Requirements

Setting up an Inverse operation requires the following:

  • Source and Target Coordinate Points

  • Source and Target Point Coordinate systems, both on the same Datum

The Distance, Azimuth, and Back Azimuth will be calculated from those parameters.

How to set up the Inverse Calculation:

  1. Under Source Point, enter a name (optional) and the coordinates for the source point.
  2. Under Source Coordinate System, select the coordinate system that corresponds to the coordinate to be converted.

    • Use to search the Datasource. The Select Source System dialog will display, and you may narrow the search by entering a search string into the Search field or browse the Coordinate Systems folders. Use the i icon to see information on each CRS. For more information on choosing a Coordinate Reference System (CRS) see the Datasource Search.

    • The default Source Coordinate System is WGS 84 [EPSG:4326], but recently used coordinate systems will populate the Source Coordinate System dropdown.

      • The units for the source and target systems will be automatically populated with the units defined in the selected objects. You may optionally use to search for and change the source or target units for the calculation.
    • To perform a vertical transformation, additionally set the source Vertical Coordinate System. Use to search the Datasource and select a vertical CRS.
      • Once a Vertical Coordinate System has been chosen, the option to input the source point height (elevation) value will appear. The vertical unit can be changed if necessary.
    • Format and precision options can be accessed by using to launch the Select Format dialog.

    • Latitude and longitude accept various input formats beyond decimal degrees. The formats that you can select are shown below with an example (all examples represent the coordinate: South 44 degrees, 30 minutes, 15 seconds):

      • DD. (example: -44.50416 or 44.50416 S)

      • DD MM. (example: -44 30.2500 or 44 30.2500 S)

      • DD-MM. (example: -44-30.2500 or 44-30.2500 S)

      • DD MM SS. (example: -44 30 15.000 or 44 30 15.000 S)

      • DD-MM-SS. (example: -44-30-15.000 or 44-30-15.000 S)

      • DD.MM (example: -44.3025 or 44.3025 S)

      • DD.MMSS (example: -44.3015 or 44.3015 S)

      • Packed DMS (example: -44301500 or 44301500S)

      • Packed DMS. (example: -443015.00 or 443015.00S)

      • Packed DM. (example: -4430.2500 or 4430.2500S)

      • Brazil ANP (example: -44:30:15,000)

      The direction (N/S/E/W) can be entered as either a prefix or suffix.

  3. Set the Target Coordinate System using the same steps as above (remember the target system must use the same datum as the source).

  5. Under Transformation, select the Operation Type drop-down to select Inverse.

  6. Choose a method: Geodesic (Great Circle), Rhumb Line (constant azimuth), or Grid distance (valid only for projected coordinates).

  7. Click Process to convert the point and populate the Distance, Azimuth, and Back Azimuth fields.

Note: The Source and Target fields can be reversed using the arrow button. This reverses the Operation Direction (left-to-right versus right-to-left). The arrow will reverse to indicate the direction.