Creating a Custom Coordinate System in SonarWiz 7.09.04 or earlier.

Owned by David Finlayson
Last updated: 2022-10-11
10 min read

SonarWiz Version 7.09.05 uses a new geodetic engine. Please refer to the User Guide for instructions on created custom coordinate systems in newer versions of SonarWiz, or contact customer support for assistance,

Introduction

In order to create a custom coordinate system in SonarWiz, you will need three things:

  1. An Earth Ellipsoid

  2. A Geodetic Datum

  3. A Map Projection

Typically, it is the Geodetic Datum transformation parameters that need to be updated and you can use one of the ellipsoids and map projections already available in the Geodetic Database.

CTI Technical Support will create custom coordinate systems for customers with active EMAs. Please see for more information.

Create a New Earth Ellipsoid

An Earth Ellipsoid is a mathematical model of the Earth’s form used as a reference frame for geodesic computations. An ellipsoid is defined in SonarWiz by two parameters:

  1. Equatorial Radius (distance from the center of the earth to the Equator)

  2. Polar Radius (distance from the center of the Earth to the poles)

You probably don’t need to create a new ellipsoid. SonarWiz installs more than 100 standard ellipsoids. The most common: WGS84 and GRS1980 are built it.

To Create a New Ellipsoid:

  1. Open the CTI Geodesy Tool. In SonarWiz, Select the Tools Ribbon > Geodesy Utility…




  2. Select a coordinate system in the main window.




  3. Click the Create… | Create Ellipsoid… button




  4. Click the New button on the Ellipsoid Dictionary Editor.


     

  5. In the New Dictionary Entry Key Name dialog, give the ellipsoid a new name. All user-defined ellipsoid names MUST start with a colon character (“:”).


    If you check the Preserve existing definition data for editing, the values for the Clarke 1880 ellipsoid will be copied into your new user-defined ellipsoid to make modifying. Click the OK button to save the name.

  6. The Ellipsoid Dictionary Editor will open the new ellipsoid page allowing you to define the Equatorial Radius and the Polar Radius. You can also add a Description and Source for the ellipsoid to help users find the correct ellipsoid in the future.

     

  7. Click the Save button to add the new ellipsoid to the Geodesy Database.

Create a New Geodetic Datum

A Geodetic Datum is a coordinate system and a set of reference points used for locating places on the Earth. In SonarWiz, a Datum defines the transformation from the desired coordinate system to WGS84. A Datum is defined in SonarWiz by two parameters:

  1. An Earth Ellipsoid (see above)

  2. A Transformation algorithm used to convert the new datum to WGS84

To Create a New Geodetic Datum:

  1. Select an existing coordinate system in the CTI Geodesy Tools main window.

  2. Select Create… | Create Datum… command


     

  3. In the Datum Dictionary Editor, select a datum similar to the new datum you wish to define in the Datum Key Name drop down window. Then click the New command


     

  4. In the New Dictionary Entry Key Name, enter a name for your new datum. All user-defined datum MUST begin with the colon character “:” (as shown below). Click the OK button to continue.


     

  5. In the Datum Dictionary Editor, enter Description and Source text. Note that the description of the datum will be used in the WKT output as the Datum Name.


     

  6. In the Datum Dictionary Editor, select the Ellipsoid to be used in the new datum.


     

  7. In the Datum Dictionary Editor, select the Technique used to convert to WGS84 and fill in the transformation parameters:



    There are three important notes here:

    First, the Description text of the datum will be used as the NAME component of the Well Known Text (WKT) field in projections using this datum. For example, the above Datum shown in the dialog is represented in WKT by “Nahrwan_1967” in *PRJ files. So, if your software is sensitive to the text in this field, be sure to use an appropriate descriptions here.


    GEOGCS[":Nahrwan67-ADNOC.LL", DATUM["Nahrwan_1967", SPHEROID["Clarke 1880, RGS",6378249.145,293.46500608], TOWGS84[-233.4000,-160.7000,381.5000,0.000000,0.000000,-0.554000,0.22630000]], PRIMEM["Greenwich",0], UNIT["Degree",0.01745329251994]]


    Second, please pay attention to the sign and units of the transformation parameters. SonarWiz needs the transformation from the new datum to WGS84. If your program reports the parameters from WGS84 to the new datum (the opposite convention), simply reverse all of the signs on the required parameters.

    Third, there are two 7-parameter shifts available in the Technique used to convert to WGS84 drop-down dialog. You must pick the version that matches your transformation definition in order for the coordinate conversion to work properly. The two 7-parameter options are:

    Seven-Parameter Transformation - This is a 7-parameter (Bursa-Wolfe) Transformation using Coordinate Frame Rotations,
    Bursa/Wolfe Transformation - This is a 7-parameter (Bursa-Wolfe) Transformation using Position Vector Rotations.

    If you are unsure which type of transformation you require, you may need to experiment with both of them and verify against your test coordinates.

  8. Click Save to save the datum to the geodetic database.

Create a New Coordinate System

A Geographic Coordinate System is a coordinate system that enables every location on Earth to be specified by a set of numbers such as latitude, longitude and elevation. To specify a location on a plane requires a map projection. In SonarWiz, a Coordinate System is defined by:

  1. A map projection, so that coordinates on Earth are referenced to a grid (easting, northing, depth)

  2. A datum transformation from WGS84 (see above)

In order to add a new Coordinate System to the geodetic database, SonarWiz requires two coordinate systems with nearly the same name to be created:

  1. :example.LL

  2. :example

It is critical that both coordinate systems exist in the database for SonarWiz to function properly. The first of these with the “.LL” extension is used internally by the program to perform reverse transformations, it is stored in the latitude/longitude projection group. The second, which must have the identical name except dropping the .LL extension, is the fully defined coordinate system and map projection the user needs. The second CS is stored in the User Defined Coordinate Systems group.

To Create a New Coordinate System

  1. Select an existing coordinate system in the CTI Geodesy Tools main window.

  2. Click the Create… | Create Coordinate System… button


     

  3. In the Coordinate System Editor, click the New button.


     

  4. In the New Dictionary Entry Key Name, enter a name for your new coordinate system. All user-defined coordinate systems MUST begin with the colon character “:” (as shown below). The convention in SonarWiz is to name the coordinate system :<datum>-<map projection>.LL. Click OK to continue.



    IMPORTANT: It is critical that the name used here start with a colon (“:”) and end in “.LL”. You may need to abbreviate the name to make sure the .LL portion fits.

     

  5. The Coordinate System Editor consists of 4 tabs which must be defined.

    Identification Tab:

    Fill out the Description and Source text as desired.
    Ensure the the Group is set to: Latitude/Longitude.
    The other fields are optional.


    General Tab

    Set the Projection drop down to “Null Projection, produces/processes Latitude & Longitude”
    Select the desired Datum using the Datum button.
    Select the desired Ellipsoid using the Ellipsoid button
    Set the Scaling, Units and Quadrant as shown below


    Origins Tab

    Set all the values in this tab to zero as shown below


    Extents Tab

    Set all the values in this tab to zero as shown below:


    Parameters

    Set all the values in this tab to zero as shown below:

  6. Click the Save button

     

  7. You should now see your new datum (with .LL extension at the top of the main display):


     

  8. Click the Create… | Create Coordinate System… button.

  9. On the Coordinate System Editor, use the Browse button to find a template coordinate system that is similar to the desired output coordinate system you are trying to define. The most important part to match is the map projection as these have a lot of parameters to fill out. In the example shown below, we have selected Nahrwan67.UTM-39N as a template coordinate system. That will set up all of the parameters for using the Clarke 1880 ellipsoid and UTM 39 North map projection.


     

     

  10. Click New on the Coordinate System Editor to define the new coordinate system.


     

  11. In the New Dictionary Entry Key Name dialog, enter the New Key Name for the new coordinate system. It should match exactly the name you picked in Step 4 above except that you will drop the “.LL” extension. Be sure to check the Preserve existing definition data for editing check box to copy in all the settings from your template coordinate system selected in Step 9.


     

  12. The Coordinate System Editor consists of 4 tabs which must all be defined.


    Identification Tab:


    Fill out the Description and Source text as desired.
    Ensure the the Group is set to: User Defined Coordinate Systems
    The other fields are optional.



    General Tab

    The Projection drop down should be set by the template you selected in Step 9.
    Select the desired Datum using the Datum button. It should match what you picked in Step 5 above.
    Select the desired Ellipsoid using the Ellipsoid button. It should match what you picked in Step 5 above.
    Keep the Scaling, Units and Quadrant as they were set from the template in Step 9.



    The Origins, Extents and Parameters tabs should all be filled out to match your template coordinate system from Step 5 above. Make any necessary modifications.

  13. Click the Save button to save the new coordinate system.

  14. Verify in the main Coordinate System List that you have successfully added two coordinate systems with nearly the same name:



    As shown in the example above, there are two newly defined coordinate systems:

    :NHRN67-Qatar-UTM39N - This is a UTM Zone 39 projection using the custom ellipsoid and datum we defined above in Steps 10-13
    :NHRN67-Qatar-UTM39N.LL - This is a latitude / longitude null projection using the custom ellipsoid and datum we defined above in Steps 3-6.

    The names are identical except for the addition of “.LL” to the latitude / longitude version.

  15. Click the Test button on the CTIGeodesyTools dialog

  16. Test that the datum transformation coordinate system is working:

    Set the Input Coordinate System Key Name to: LL84 (This is WGS84)
    Click the “B” button in the Result box and set the Group to Latitude / Longitude.
    You should see your first coordinate system (the “LL” version) at the top of the Key Name list.



    Enter test Latitude and Longitude coordinates into the Input box
    Click the Calculate button
    Verify that the datum transformation from WGS84 to your output Datum produced the expected results.

     

  17. Test that the map projection version of the coordinate system is working:


    Set the Input Coordinate System Key Name to: LL84 (This is WGS84)
    Click the “B” button in the Result box and set the Group to User Defined Coordinate Systems.
    You should see your second coordinate system (the one without the “LL” ) at the top of the Key Name list.


    Enter the test Latitude and Longitude coordinates into the input box
    Click the Calculate button
    Verify that the Easting and Northing coordinates produced the expected results.

Sharing Coordinate Systems with Other SonarWiz Installations

Custom coordinate systems can be transferred between SonarWiz installations by sharing special GXP files created for this purpose. Remember, you need to export both coordinate systems defined above (the “LL” version and the plain version) to make a complete set. SonarWiz will not function properly unless both versions are installed.

See the article for instructions.

Copyright 2022, Chesapeake Technology, Inc.