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Custom coordinate system setup

This guide shows how to set up a custom coordinate system in ReachView 3 if you cannot find the required one and know its parameters.

To configure the custom coordinate system, you can use 4 different properties:

  • Ellipsoid your datum is based on
  • Projection type and its parameters
  • Transformation type and its parameters
  • Geoid model
tip

Since not every group of parameters is required for a coordinate system configuration, you may omit some of them and only use the parameters that you have for your transformation.

  • If the projection is performed from the same datum the base set up, you skip the transformation step
  • If you decide to work with ellipsoidal height, you do not select the geoid model
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On some Android devices, default keyboards do not provide a minus sign. To get access to it, we recommend downloading Gboard, a virtual keyboard app, from the Google Play Store.

To show all features of this tool, we will walk you through the example of transformation from GDA2020 datum to GDA94, performing MGA zone 51 projection, and applying the AUSgeoid2020 geoid model to GDA2020 datum.

Run the New Coordinate System tool​

When picking a coordinate system for your project, tap the Coordinate system section and click on the plus button placed in the right top corner.


It will open the New Coordinate System screen.

Define the Coordinate System name​

Enter the name of your custom coordinate system. Using this name, you will be able to find it in the list of coordinate systems later on. We will name the coordinate system GDA94 / MGA zone 51 [GDA2020 base].

Specify ellipsoid for datum​

note

In this section, we set up the ellipsoid the datum based on. This step is mandatory.

By default, the GRS80 ellipsoid is used. To change it, click on Ellipsoid and choose the required one from the list. It will update the Semi-major axis and 1/f parameters accordingly.


The GDA94 datum uses the GRS80 ellipsoid, so we leave it as is.

Once the horizontal datum is set up, go back to the New Coordinate System screen.

tip

If the required datum is missing, contact us at support@emlid.com.

Apply projection​

  1. Go to the Projection screen.

  1. Choose the required projection type: Transverse Mercator, Oblique Mercator (Variant A), Oblique Mercator (Variant B), Lambert Conic Conformal (1SP), or Lambert Conic Conformal (2SP) projections.

    We perform Transverse Mercator projection.


  1. Enter the projection parameters.

  1. Click on the Save button.

Specify transformation parameters​

note

You need to configure this option only if your coordinate system uses the datum that differs from the base's one.

  1. Go to the Transformation screen and switch it on.

  1. Choose the required transformation type: Helmert or Molodensky-Badekas.

    We need Helmert transformation to go from GDA2020 to GDA94 datum.

  2. Fill in the transformation parameters: there are 7 of them for the Helmert transformation and 10 for Molodensky-Badekas.

    tip

    The tool handles transformations with 3, 4, and 6 parameters as well. You can type in only the parameters you have and leave the others empty.


  1. Click on the Save button.

Choose the geoid model​

note

Apply geoid model to your custom coordinate system only if you require orthometric height for your project. ReachView 3 applies geoid correction to the datum the base works with, so make sure to choose the appropriate one.

  1. Go to the Geoid screen and switch it on.

  1. Click on the Model and look for the appropriate geoid file.

    We choose the AUSgeoid2020 that meant to be used for coordinates in GDA2020.

    The app will suggest you download the geoid model if you have not done it earlier.


  1. Once the geoid is downloaded, tap on the Save button.

Save the Coordinate System​

Once everything is configured, tap on the Save button in the New Coordinate System screen to save the coordinate system.

You can continue creating the New project to start working with it or find your coordinate system later while working with any other project. Custom coordinate systems will show up first in the Coordinate System list.