Coordinate System

The Coordinate System dialog provides a system for choosing a coordinate system.  The terms projection and coordinate system are used as interchangeable synonyms in Manifold.  The dialog appears in three settings:

 

 

 

 

 The Coordinate System dialog allows us to choose a coordinate system from three groups of available coordinate systems, totalling thousands of options:

 

 

 

 

The Coordinate System dialog will launch with the current coordinate system in use automatically selected in the lists of known systems, with the parameters of the current coordinate system loaded into controls in the Custom tab.  The tab selected when the dialog launches will be the tab containing the list of systems within which the current system is listed.    If the starting system is not found in any list, the dialog launches with the Custom tab.

Standard Tab

il_coordsys_standard.png

Standard Tab Controls

Standard

A long list of coordinate systems known by their names, either by well-established tradition or by government designation in various countries.  The list will be scrolled to the coordinate system currently in use, if it appears in the list.

EPSG

A comprehensive list of coordinate systems from the EPSG Geodetic Parameter Dataset published by IOGP.

Custom

Specify a custom coordinate system by choosing a base coordinate system (ellipsoid) and a standard type from a list of configurable coordinate systems.

(Filter Box)

Our best friend when sifting through long lists.   Enter text, such as Mercator into the filter box and only those projections which include that text in their names will be displayed.  

(list pane)

Click on a coordinate system in the list to choose it.

(lower pane)

The dialog opens with the current coordinate system displayed in JSON format in the lower pane, as seen in the illustration above.  Details for a chosen coordinate system will be displayed in JSON format in the lower pane, as seen below.

Metrics

Units of measure, including unit, scales, and offsets.  An asterisk * character by the units of measure abbreviation, as in ft*,  indicates a custom unit has been defined using  the Coordinate System Metrics dialog.

btn_metrics_xy.png

Set use of default metrics or edit metrics by launching the Coordinate System Metrics dialog.

Force XY axes

Force the coordinate system to always use XY axis ordering.  A defensive measure against data that specifies use of YX axis ordering but which in reality uses XY ordering.  See the That YX Thing essay.  

Axes

Current axis ordering.   H means "height", also referred to as Z.

 

 

Clicking a coordinate system in the Standard tab list will immediately show details for that coordinate system:

 

il_coordsys_standard_details.png

Filter Box

The Filter box provides much-needed help when trying to find a desired coordinate system in a very long list.   The dialog displays only those coordinate systems which contain in their names the text entered into the Filter box.  If Lambert is entered into the Filter box the list will display only those coordinate systems with Lambert in their names.

 

il_coordsys_standard_filter.png

EPSG Tab

The EPSG tab provides a staggeringly long list of coordinate systems from the EPSG Geodetic Parameter data set published by IOGP.  Each has a text name and the official EPSG code in parentheses.  The only rational way to find a desired EPSG coordinate system is to use the Filter box to find it by entering the EPSG code into the Filter box.

 

il_coordsys_epsg.png

EPSG Tab Controls

Standard

A long list of coordinate systems known by their names, either by well-established tradition or by government designation in various countries.  The list will be scrolled to the coordinate system currently in use, if it appears in the list.

EPSG

A comprehensive list of coordinate systems from the EPSG Geodetic Parameter Dataset published by IOGP.

Custom

Specify a custom coordinate system by choosing a base coordinate system (ellipsoid) and a standard type from a list of configurable coordinate systems.

(Filter Box)

Our best friend when sifting through long lists.   Enter text, such as Mercator into the filter box and only those projections which include that text in their names will be displayed.  

(list pane)

Click on a coordinate system in the list to choose it.

(lower pane)

The dialog opens with the current coordinate system displayed in JSON format in the lower pane, as seen in the illustration above.  Details for a chosen coordinate system will be displayed in JSON format in the lower pane, as seen below.

Metrics

Units of measure, including unit, scales, and offsets.  An asterisk * character by the units of measure abbreviation, as in ft*, indicates a custom unit has been defined using  the Coordinate System Metrics dialog.

btn_metrics_xy.png

Set use of default metrics or edit metrics by launching the Coordinate System Metrics dialog.

Force XY axes

Force the coordinate system to always use XY axis ordering.  A defensive measure against data that specifies use of YX axis ordering but which in reality uses XY ordering.  See the That YX Thing essay.  

Axes

Current axis ordering.   H means "height", also referred to as Z.

 

 

 

The EPSG tab includes all EPSG codes, including those (marked with a red ! message icon) that have been deprecated or otherwise are discouraged by the EPSG system.

 

il_coordsys_epsg_details.png

 

Clicking on a coordinate system will select it and will display details in the lower pane.   Text comments from the EPSG database are provided as ordinary text while the coordinate system definition is reported in JSON format.   To understand EPSG commentary, consult documentation published by IOGP.

Custom Tab

Manifold provides the ability to create a custom coordinate system by customizing a starting coordinate system chosen from a list of configurable Types.  Most custom coordinate systems are simply variations on a relatively limited list of frequently utilized coordinate system types so this approach can cover a very wide range of possibilities should a coordinate system be required that is not included in the thousands of EPSG plus standard coordinate systems.

 

A  common use of Custom is usually to specify an azimuthal coordinate system, like Orthographic, or other coordinate system that is centered precisely upon a specific area of interest.  See the Example: Change Projection of an Image  topic for a typical example.

 

il_coordsys_custom.png

 

To specify a custom coordinate system:

 

  1. Provide a Name for the new system.  

  2. Choose a starting Type of coordinate system.

  3. Choose a Base if an ellipsoid other than WGS84 is desired.

  4. Specify desired parameters. Parameter boxes will be displayed as options as required based what is selected in the Type box.

  5. Adjust Metrics as desired.

  6. Press OK.

 

Custom Tab Controls

Standard

A long list of coordinate systems known by their names, either by well-established tradition or by government designation in various countries.  The list will be scrolled to the coordinate system currently in use, if it appears in the list.

EPSG

A comprehensive list of coordinate systems from the EPSG Geodetic Parameter Dataset published by IOGP.

Custom

Specify a custom coordinate system by choosing a base coordinate system (ellipsoid) and a standard type from a list of configurable coordinate systems.

Name

Choose something more useful and self-documenting than the default of "Custom Coordinate System."   That will help remind us what we did should we use this project or data years later.

Type

A list of configurable coordinate systems.  Choosing one of those will configure the parameter boxes to provide allowed options.

Base

The "base coordinate system," also classically known as the ellipsoid or datum.

btn_datum.png

Click to edit the Base Coordinate System, choose from a list of favorite base coordinate systems, or to edit the list of favorite base coordinate systems.

(Parameter boxes)

Configuration parameters allowed by the Type of configurable coordinate system selected.

 

When editing parameters for a custom coordinate system, the system will detect invalid parameter values and will suggest correcting them before the dialog is closed.

btn_metrics_unit_converter.png

Appears next to parameter boxes for some coordinate systems.  Click to open a dropdown menu with two choices to alter the parameter:

 

Use Default Value- resets the parameter to the default value. If the parameter is already set to the default value, a check icon will appear next to the Use Default Value command.

 

Unit Converter - Launch the Unit Converter dialog to allow easy conversion of units and values for this parameter.

Metrics

Units of measure, including unit, scales, and offsets.  An asterisk * character by the units of measure abbreviation, as in ft*, indicates a custom unit has been defined using  the Coordinate System Metrics dialog.

 

False easting and false northing parameter values will be displayed in the units of measure specified for the coordinate system.   Changing units of measure for a custom coordinate system will automatically re-scale false easting and false

northing values to the new units.

btn_metrics_xy.png

Set use of default metrics or edit metrics by launching the Coordinate System Metrics dialog.

 

The Use Default Metrics command resets metrics to the default values for the coordinate system. If coordinate

system metrics are already set to the default values, a check icon will appear next to the Use Default Metrics choice in the menu.

 

The Edit Metrics command launches the Coordinate System Metrics dialog.

Force XY axes

Force the coordinate system to always use XY axis ordering.  A defensive measure against data that specifies use of YX axis ordering but which in reality uses XY ordering.  See the That YX Thing essay.  

Axes

Current axis ordering.   H means "height", also referred to as Z.

 

To learn how to add a favorite coordinate system or a favorite base coordinate system, see the Example: Adding a Favorite Coordinate System topic.

Choosing the Type

Custom coordinate systems are created by specifying custom parameters for a configurable coordinate system.  Manifold provides a list of popular configurable systems in the Type box.   To choose one of those we click on the down arrow icon at the right of the box.

eg_change_proj_image01_04.png

 

Doing so opens up the list of available configurable coordinate systems.  We choose a system by clicking on it to highlight it.

 

eg_change_proj_image01_05.png

 

Above we have selected Orthographic as the Type.    Once we choose a configurable Type we can customize the coordinate system by specifying parameters of interest.

 

eg_change_proj_image01_06.png

 

Manifold will automatically provide option boxes for parameters that may be customized for a particular system.   Option boxes have indicators what units of measure are used, for example, m for meters and deg for degrees or ft for feet.   An asterisk * character by the units of measure abbreviation, for example, as ft*,  indicates a custom unit has been defined using  the Coordinate System Metrics dialog.  Enter values to customize the starting coordinate system to create the specific custom coordinate system desired.  When finished, press OK.

 

The default values for Center latitude and Center longitude for Orthographic projection, as with most projections, are 0 and 0, thus centering the projection on the 0,0 intersection of the Prime Meridian and the Equator in the ocean off the coast of Africa.  Unless our task is to work with maps of an empty stretch of ocean (or the bathymetry deep below) we will want to change the Center latitude and Center longitude values to a location somewhere near the center of our area of interest.

 

eg_change_proj_image01_06a.png

 

The illustration above shows Orthographic customized to be centered on the state of Florida in the United States, a useful coordinate system for creating maps of Florida.

 

il_coordsys_custom_krovak.png

 

When a starting Type of coordinate system provides too many options to fit at once into the display a scroll bar will appear to allow us to scroll through all of the options.  The Modified Krovak Oblique Conformal Conic (North) coordinate system lives up to the promise of its long name by providing almost two pages of configurable parameters.

 

tech_tina_sm.png

Tech Tip:  Beginners can accomplish much with default projections such as Pseudo-Mercator.   Use Pseudo-Mercator for general display, learn how to use Orthographic well when local measurements are important, and get to know the limits and uses of Latitude / Longitude.   As expertise grows, we can learn how and when to use other projections.   Usually we will encounter new and confusing projections not because we want to use them, but because we receive data created by somebody else that uses those projections.

 

Manifold provides a seemingly endless range of coordinate systems with seemingly endless options.  So many options can be difficult for beginners to understand, but those options are there not because of a desire to make life difficult for beginners.   Instead, those options are there because over the course of centuries experts around the world have developed very many sophisticated and endlessly varied projections to match precisely the requirements of their tasks.   There are very good reasons why the Krovak family of coordinate systems has so many options.   

 

Teaching such systems and how to correctly use them is beyond the scope of this documentation.   Users who need to use them or who would like to learn more should take advantage of the world's extensive resources, many of which are online, that teach geodesy, computational cartography, mathematics and so on.   Read a book or take a course at a local college - you may find yourself addicted to the field, as computational cartography often becomes a hobby for non-cartographers.  The most gifted computational cartographer of all in modern times, John Parr Snyder, began his career as an amateur hobby.   He became a legendary professional in the field after solving a complex problem the professional cartographic bureau at USGS could not.

Base Coordinate Systems

The Base option allows us to customize the coordinate system by choosing the base coordinate system, that is, the Earth ellipsoid model used.  See the discussion in the Base Coordinate System dialog topic.

Notes

Synonyms -  Classic cartographers favor the term projection while programmers seem to prefer coordinate system.  This documentation uses the two terms interchangeably, with the term projection tending to be used more in GIS or display contexts and the term coordinate system tending to be used more when discussing programming, SQL or standards.

 

Bases are Basic - All coordinate systems are based upon a model of the Earth's sphere or ellipsoid that specifies the size and shape of the Earth using various parameters such as radius, eccentricity, center of rotation and so on.   Such models have usually been referred to by cartographers and GIS people as the ellipsoid or datum but the more popular term among computer people now is becoming the base, short for base coordinate system.  Manifold tends to use the terms base, base coordinate system, ellipsoid and datum as interchangeable synonyms since that is how most people working with spatial data know the terms.  

 

All spatial data in any projection, including Latitude / Longitude, assumes some base even if the base is not explicitly specified as is often the case with data where latitude and longitude numbers specify a location.   If precision is required it is important to know what base is assumed because different bases used with exactly the same type of coordinate system and exactly the same numeric data can result in differences of hundreds of meters in the position of a location.   

 

We might not care about what base was used if we are creating maps that display an entire continent, for example,  where it does not matter if the dots that represent cities vary in position by a few hundred meters, but in other applications such as guiding an emergency medical response vehicle to the correct entry portal for a hospital and not into water in an adjacent lake, or determining whether a specific real estate parcel falls within a special planning zone or taxation zone, a few hundred meters can matter very much.   See the Latitude and Longitude are Not Enough topic for a visual example of how varying bases can move the position of exactly the same coordinates.

 

Rotation Parameters - Custom coordinate system parameters for rotation factors are displayed in degrees and support the conversion of units.

See Also

Coordinates

 

Projections

 

Assign Initial Coordinate System

 

Change Coordinate System

 

Map Projection

 

Coordinate System Metrics

 

Unit Converter

 

Base Coordinate System

 

Favorite Coordinate Systems

 

Favorite Base Coordinate Systems

 

Example: Assign Initial Coordinate System - Use the Contents pane to manually assign an initial coordinate system when importing from a format that does not specify the coordinate system.

 

Example: Change Projection of an Image - Use the Change Coordinate System command to change the projection of an image, raster data showing terrain elevations in a region of Florida, from Latitude / Longitude to Orthographic centered on Florida.

 

Example: Adding a Favorite Coordinate System - Step by step example showing how to add a frequently used coordinate system to the Favorites system.

 

Example: Detecting and Correcting a Wrong Projection - A lengthy example exploring projection dialogs and a classic projection problem.  We save a drawing into projected shapefiles and then show on import how a projection can be quickly and easily checked and corrected if it is wrong.

 

Re-Projection Creates a New Image - Why changing the projection of an image creates a new image.

 

About Coordinate Systems

 

Projections Tutorial

 

Latitude and Longitude are Not Enough