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Set up custom coordinate system

tip

We recommend setting up the projects indoors before the survey as some

coordinate systems

Coordinate system is a coordinate-based local, regional or global system used to locate geographical entities. A spatial reference system defines a specific map projection, as well as transformations between different spatial reference systems.

require additional downloads in Emlid Flow.

This guide describes how to set up a custom

coordinate system

Coordinate system is a coordinate-based local, regional or global system used to locate geographical entities. A spatial reference system defines a specific map projection, as well as transformations between different spatial reference systems.

in Emlid Flow or Emlid Flow 360 if you cannot find the required one and know its parameters.

Overview​

note

You can only configure the

coordinate system

Coordinate system is a coordinate-based local, regional or global system used to locate geographical entities. A spatial reference system defines a specific map projection, as well as transformations between different spatial reference systems.

while creating a new project.

To configure the custom

coordinate system

Coordinate system is a coordinate-based local, regional or global system used to locate geographical entities. A spatial reference system defines a specific map projection, as well as transformations between different spatial reference systems.

, you can use 4 different properties:

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

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 projection.

  • If the projection is based on the same datum as the base, skip the transformation step.
  • If you decide to work with ellipsoidal height, don’t select the geoid model.
tip

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

note

You can set a coordinate system as default for all of your future projects. With this feature, you can apply settings faster. Learn more in Create or Import Project guide.

Workflow​

Creating custom CS​

When picking a coordinate system for your project, follow the steps below:

  1. On the Edit project coordinate system screen, click Use custom.

  2. To create a custom coordinate system, click the + New button.

  3. 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 name the coordinate system GDA94 / MGA zone 51 [GDA2020 base].

Specifying ellipsoid for datum​

note

This step is mandatory.

In this section, we set up the ellipsoid the datum based on. By default, the GRS 1980 ellipsoid is selected. To change it, click the Ellipsoid cell and find the required ellipsoid from the list.

note

It updates the Semi-major axis and 1/f parameters accordingly. You can access these parameters by clicking the information icon on the right side of the Ellipsoid cell.

The GDA94 datum uses the GRS 1980 ellipsoid, so we leave it as is.

note

If the required datum is missing, contact us at [email protected].

Applying projection​

  1. To configure projection, click the Projection cell.

  2. Choose the required projection type:

    • Albers Equal Area Conic
    • Krovak
    • Lambert Conic Conformal (1SP)
    • Lambert Conic Conformal (2SP)
    • Mercator (Variant B)
    • Oblique Mercator (Variant A)
    • Oblique Mercator (Variant B)
    • Oblique Stereographic Alternative
    • Transverse Mercator

    We perform the Transverse Mercator projection.

  3. Enter the projection parameters.

  4. Save changes.

Specifying transformation parameters​

note

You need to configure this option only if your

coordinate system

Coordinate system is a coordinate-based local, regional or global system used to locate geographical entities. A spatial reference system defines a specific map projection, as well as transformations between different spatial reference systems.

uses a datum that differs from the base's one.

  1. Click the Transformation cell.

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

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

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

    tip

    The app can also perform transformations only with 3, 4, and 6 parameters. You can type in the parameters you have and leave the others empty.

  4. Save changes.

If your custom CS requires inputting parameters for horizontal adjustment, you can specify them in the Horizontal adjustment cell:

  1. Click the Edit button next to the Horizontal adjustment cell.

  2. Select Helmert 2D for horizontal adjustment.

  3. Specify the parameters and tap Save.

Choosing geoid model​

note

Apply the geoid model to your custom coordinate system only if you require orthometric height for your project. Emlid Flow 360 applies geoid correction to the datum the base works with, so make sure to choose the appropriate one.

Click the Geoid model cell and select the appropriate geoid file from the list.

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

If your custom CS requires inputting parameters for vertical adjustment, you can specify them in the Vertical adjustment cell:

  1. Tap the Vertical adjustment cell.

  2. Enable vertical adjustment.

  3. Specify the parameters and tap Save.

Saving custom CS​

Once everything is configured, click Create coordinate system on the New coordinate system screen to save the coordinate system. From now on, your custom coordinate system is saved to your Emlid account and synced among all your devices.

You can find your custom coordinate systems on the My coordinate systems screen.

You can continue creating the project for survey.

Editing custom CS​

You can edit parameters of your custom CS in the Emlid Flow 360 app. To do so, follow these steps:

note

The editing option is not available for calibrated systems.

  1. Open menu o the left, and tap Coordinate systems. The list of your custom CSs will open.

  2. Tap the three dots button to rename, duplicate, edit or check the information about your custom CS.

    tip

    Duplicating your CS allows you to quickly edit parameters without having to enter them twice.

  3. Edit the parameters and tap Create coordinate system.

Further reading​