Projection Explorer

Coordinate System Selection, Creation and Exploration Dialog

The coordinate system selection dialog allows you to choose a coordinate system from a large range of predefined and user-defined coordinate systems.

With this dialog, you can –

  • Select a coordinate system or select “no coordinate system”.
  • Define a new coordinate system.

 

The dialog is also available to users as a stand-alone application called the Projection Explorer.

Projection Explorer is now an integral part of ProRaster and can be found in all tiers of that product family. The video below shows how to use coordinate systems in ProRaster and how to use the ProJection Explorer dialog to select coordinate systems.

Projection Explorer: Mollweide

The Projection Explorer dialog showing a preview of the Mollweide projection.

You make a coordinate system selection by selecting the appropriate category in the category drop-list and then the appropriate member in the member list located immediately below it. The selected coordinate system will be displayed in the title bar of the dialog. If you wish to choose “no coordinate system”, a button is provided to clear the category and member lists.

As an alternative to navigating these lists, the dialog can help you find and select a coordinate system in a few ways. Firstly, it records all the coordinate systems you have selected in the past and displays them in the “Recent Selections” category. Secondly, you can search using a text string which will list all coordinate systems that may approximately match that string. Finally, you can search by double-clicking on the world map to see a list of coordinate systems which may be suitable choices for that location.

In the MapInfo Pro ecosystem, coordinate systems are defined in a text file called MAPINFOW.PRJ which you will find in the Professional directory of your MapInfo Pro installation. In this file, coordinate systems are separated into more than 150 categories (or groupings), and in each category, there will be one or more members, each of which represents a coordinate system.

Each member will have a descriptive string and a set of numeric (and sometimes text) parameters which define all the coordinate system elements such as the spheroid, datum, and projection. To understand the parameters and learn how to define a coordinate system using parameters, you will need to refer to the MapInfo Pro User Guide.

This long-standing mechanism for using coordinate systems and projections in MapInfo Pro is at odds with more recent systems which are more likely to use EPSG codes or a well-known-text representation of the coordinate system data. Support for EPSG codes is provided by embedding the code in the member description text preceded by a “\p” character sequence. To learn more about EPSG codes and find coordinate system definitions by code, you can explore these websites – https://epsg.org/home.html, https://epsg.io/, https://spatialreference.org/.

The dialog is split into three zones – the “control” zone (A) in the top left, the “world map” zone  (C) along the bottom, and the “projected map” zone (B) in the top right.

The three control zones of the Projection Explorer dialog. The world map has been used to obtain suggested coordinate systems for California and a local projection has been selected.

The control zone contains the category and member lists which define the currently selected coordinate system. This will be reflected in the dialog title. You can get detailed information about the coordinate system by clicking the information button located to the immediate right of the member list. You can search for coordinate systems by clicking the search button located to the right of the category list. The clear button allows you to select “no coordinate system”. The category list contains two special categories – the “Recent Selections” category, located at the very top of the list, and the “User defined coordinate systems” category, located at the very bottom of the list.

Every time you use the dialog and hit “Ok” to exit, your selected coordinate system is written into the recent selections list. The next time you use the dialog, your most recent selection will be front and centre. This data is permanently cached to disk and is shared across all software developed by RGE. If you wish, you can delete all members from this list by hitting the delete button located to the right of the member list.

Using the “Recent Selections” category to choose a Popular Visualisation projection of the world.

If you select the user defined coordinate system category, then the “Add” button to the right of the member list will be enabled, and you will be able to add a new coordinate system definition. These are permanently cached to disk and shared across all software developed by RGE. If you wish, you can delete the selected member from this list by hitting the delete button located to the right of the member list. You can also edit an existing member by double-clicking on it in the list.

Using the “User defined coordinate systems” category to select a local projection for New Zealand that has been added manually.

Below the member list is the suggestions list, which will be populated with candidate coordinate systems when you double click on a location in the world map. You can click on any suggestion to select that coordinate system.

The world map is an interactive map control showing the topography, bathymetry, and countries of the world using a geographic coordinate system. The projected map is an interactive map control showing world topography and bathymetry data, reprojected into the selected coordinate system.

In either map, use the mouse wheel to zoom in and out about the mouse cursor location. To pan, click and hold the left mouse button and drag, then release the button to end panning. Both maps will automatically fit to the data extents when you zoom out beyond the maximum extent.

The world map also displays countries as transparent colored polygons, superimposed over the topography. As you zoom in, the opacity of the countries layer is increased so that they become the dominant feature of the map. As you move the mouse over the map, the geographic coordinates (longitude and latitude) are displayed in a tooltip. The tooltip also reflects the country and the province of the country that the mouse cursor is hovering over. If you left double-click the mouse in the world map, the suggestions list box will be populated with coordinate system candidates for that location. If you click on any coordinate system in the suggestions list it will become the selected coordinate system in the category and member lists.

Countries displayed as colored polygons help provide guidance when using the spatial search feature to acquire a suitable coordinate system.

The projected map displays the world topography and bathymetry reprojected into the selected coordinate system. It does not display any countries and the tooltip only reflects the cursor location. To display data in the selected coordinate system usually requires clipping the world raster to the geographic bounds of the coordinate system. This feature is not available for all coordinate systems. When reprojection is not supported the projected map uses geographic coordinates and the topographic data is displayed in greyscale rather than color. When the geographic bounds are known they are rendered in the world map as a red box.

The search dialog provides a mechanism to search for a coordinate system by approximate string matching. It searches through the category and member string collection and, as you type a string, returns a list of candidate coordinate system definitions that match the search string. For example, you can search for a coordinate system by EPSG code by simply typing in the code as the search string. Alternatively, you might enter the name of a country to find any country-specific coordinate systems. If you select a candidate coordinate system and hit “Ok” the main dialog will update to reflect that selection.

You can type an EPSG code or any text string into the search dialog to find suitable coordinate system definitions.

The information dialog provides detailed information on the selected coordinate system. This includes the category and member strings as well as the EPSG code (if known), the projection, datum, spheroid, and horizontal units. The coordinate system expressed as a MapInfo Interchange Format (MIF) string is also shown as well as the geographic (longitude and latitude) bounds. In some cases, the bounds will also be known in projected coordinates.

The Information dialog gives insight into the coordinate system parameters.

To add a user-defined coordinate system, select the “User defined coordinate systems” category (which is the very last item on the categories list), then click the add button. A dialog is presented in which you can define the member string, the EPSG code, and the parameters string.

The member string is purely descriptive and will be reflected in the member list once you add the new coordinate system. If you know the EPSG code, then enter this in the appropriate edit box rather than adding it to the member string, as the system will automatically add it to the member string for you. The most important information you must supply is the parameters string. This is difficult to construct manually and to do so you will need to refer to the detailed information provided in the MapInfo Pro Users Guide. If you hit “Ok” the new coordinate system will be added to the user-defined coordinate systems member list and the main dialog will update to reflect that selection.

If you double click on a user-defined coordinate system in the members list, the same dialog will open and allow you to edit the existing definition.

The user defined coordinate system editor dialog.

You can use this dialog to explore coordinate systems and projections and to preview maps using the selected coordinate systems. You are limited to those spheroids, datums, and projections that the MapInfo Pro system supports, and for more information on this, consult the MapInfo Pro User Guide.

The world map is displayed using a geographic coordinate system based on the WGS84 spheroid. A presentation like this is useful for displaying the entire surface of the Earth but results in increasing distortion as you move north and south of the equator. There are many other projections that address this issue in different ways, and the projected map will show you a preview of how the world will be rendered using the selected projection. A good place to start is the “Projections of the World” category where you can see the effect of projections like Mollweide, Sinusoidal, or Popular Visualisation (used by Google Maps).

Many projections are specifically designed for a particular region of the Earth. Outside of this region, attempting to project coordinates may result in mathematical failure. For projections like this, the dialog needs to know the geographic bounds of the region. If the bounds are not known, it will not attempt to preview the projection. One of the most popular local projections is Universal Transverse Mercator (UTM). UTM can be applied to any region and to facilitate this there are a large number of standard “zones” which define bounded regions. The category “Universal Transverse Mercator (WGS84)” is a good place to find UTM projections suitable for our region of interest.

Using the Projection Explorer to find a suitable coordinate system for Kalgoorlie (Western Australia), by double clicking on the world map and selecting one of the candidates offered.