Coordinate System

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

1. • Assign Initial Coordinate System - If a component is imported from a format that fails to specify the coordinate system used, we must do so manually.   Until we assign the initial coordinate system, the coordinate system read-out for that component in the Component tab of the Info pane will use red text giving the default coordinate system as a placeholder.  Once we assign the initial coordinate system the read-out will switch to black text reporting the assigned coordinate system..   This command should only be used once, immediately after initial import or linking of a component.  Assign Initial Coordinate System does not change the data in the component: it only changes how Manifold uses that data.  When we choose Assign Initial Coordinate System, a submenu appears that includes an More... choice, which in turn launches the Coordinate System dialog.

1. • Repair Initial Coordinate System - This is used to repair mistakes when assigning the initial coordinate system.  Sometimes a component is imported from a format that incorrectly specifies the coordinate system it should use, and we must manually change that initial setting to the correct coordinate system.  At other times, we might have used Assign Initial Coordinate System to specify the initial setting but we made a mistake and specified the wrong projection or a projection that is wrong in some detail.  This option allows us to repair such errors by specifying the correct initial coordinate system.  Repair Initial Coordinate System does not change the data in the component: it only changes how Manifold uses that data.  When we choose Repair Initial Coordinate System, a submenu appears that includes an More... choice, which in turn launches the Coordinate System dialog.

1. • Reproject Component - This is the routine command we use to reproject data into whatever projection we want.  Suppose, for example, we import data that is in Latitude / Longitude format but we want it to be in Pseudo-Mercator so it is a better match to web servers and so we can better measure distances.  This option allows us to reproject the data as we like. Reproject Component changes the data in the component: it recalculates the coordinate numbers in the data so they provide correct positions within the new coordinate system. When we choose Reproject Component, a submenu appears that includes an More... choice, which in turn launches the Coordinate System dialog.

 The dialogs above provide a coordinate picker button launches a drop down menu that allows choosing More... for the full Coordinate System dialog illustrated in this topic, choosing from a list of favorites (which include Latitude / Longitude and Pseudo-Mercator by default), or editing the Favorites list to add or remove favorites.

Text Names or EPSG Codes ?

In a word, "both."   Manifold provides choices of either text names for coordinate systems in the traditional manner or EPSG codes in modern style, providing access to many thousands of coordinate systems and an infinity of custom coordinate systems.   Some background:

In years past, projections have been specified using text names such as "Lambert Cylindrical Equal Area."  Text names are familiar to people who have been doing GIS for many years, but they are often a cause of ambiguity and errors since different people, different countries or different software packages might not mean exactly the same thing by a given text name.

To eliminate errors caused by lack of standardization in text names, the International Association of Oil and Gas Producers now maintain a standardized system, the EPSG database, that lists thousands of coordinate systems using EPSG codes.   Each EPSG code unambiguously specifies a coordinate system with all relevant parameters, including datums.  

Coordinate systems which are typically known by text names can be further sub-divided into two groups:  those which are defined by the name only with no further parameters required, such as the Robinson projection, and those which require both the name plus additional parameters, such as Lambert Conformal Conic  or Orthographic.  

The many thousands of coordinate systems Manifold knows therefore can be organized into three groups:  EPSG coordinate systems, named coordinate systems that do not require additional parameters, and named coordinate systems which require additional parameters.

Three Tabs: Thousands of Choices

The Coordinate System dialog lists available coordinate systems within three tabs:  an EPSG tab that lists all EPSG coordinate systems, a Standard tab that lists all text name coordinate systems for which no further parameters need be specified, and a Custom tab that allows choosing coordinate system by well-known text names plus necessary parameters.   

• Standard - A long list of coordinate systems well-known by text names, either as a result of cartographic tradition or by government designation as a standard in various countries.   Coordinate systems in the Standard tab do not require specification of any additional parameters.  The Standard tab therefore presents a long list of named projections.

• EPSG - The gold standard.  This tab provides a staggeringly comprehensive list of coordinate systems from the EPSG Geodetic Parameter Dataset published by IOGP, including all systems and transformations in the latest EPSG standard.  EPSG coordinate systems are precisely, unambiguously defined with a level of care unprecedented in international cartographic and geodesic practice.   EPSG coordinate systems are known formally by their EPSG codes but also may have a text name to provide easier discussions in more casual settings.   Many EPSG coordinate systems will also appear in the Standard tab, using whatever names came into use for those systems before rigorous standardization by EPSG.

• Custom - A tab with controls and options that allow us to invoke any of the named coordinate systems which require specification of parameters. or to specify a fully-custom coordinate system based on a list of configurable types.  

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.

The three tabs often provide three ways to get to the same coordinate system.   The same coordinate system may be known by a standard text name as well as an EPSG code, and it could also be specified by choosing an equivalent Custom type with matching parameters.  Having three ways to get to the same thing makes it more likely we can easily specify the coordinate system used by a particular data set, regardless of how that data set specifies the projection to use.

Standard Tab

Standard Tab Controls

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

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 Mercator is entered into the Filter box the list will display only those coordinate systems with Mercator in their names.

EPSG Tab

The EPSG tab provides a staggeringly long list of coordinate systems from the EPSG Geodetic Parameter data set published by IOGP.  EPSG refers to coordinate systems as projected coordinate systems.   For geodetic coordinate systems in the EPSG system, use the EPSG tab in the Base Coordinate System dialog, which can be accessed by clicking the Custom tab and then clicking the Base picker button.   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 or part of the text name into the Filter box.   

EPSG Tab Controls

The EPSG tab includes all EPSG codes.

 EPSG codes marked with a red message icon have been deprecated or otherwise are discouraged by the EPSG system.

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

The Custom tab allows us to invoke any of the named coordinate systems which require specification of parameters.  This tab also allows us to specify 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 well-known 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.

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

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.

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

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.

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.

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.

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 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.  A base coordinate system is a geodetic coordinate system, in that it is a coordinate system using latitude and longitude coordinates that incorporates both a precise description of the Earth ellipsoid used (also known as the datum) as well as the transformation method to convert coordinates in that specific geodetic system to the reference standard in Manifold, the World Geodetic 1984 (WGS84) coordinate system.

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.

Standard, Custom, etc. - The names "Standard" and "Custom" used as captions for tabs are simply short English words which are convenient: there is no intent to imply that either EPSG is not also a standard, for example.   There is simply not enough room in tabs to write "EPSG Codes," "Well-known text names that do not require further parameters," and "Well-known text names that must be customized by specifying parameters."

Bases are Basic - All coordinate systems are based in some way, through some conversions, upon a latitude and longitude coordinate system that incorporates 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, because in addition to detailed specification of the Earth ellipsoid a base coordinate system also specifies the conversion method to use to convert coordinates from that base coordinate system into the reference standard base coordinate system used by Manifold, the World Geodetic 1984 (WGS84) 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, but that is a sloppy habit.  

All spatial data in any projection, including Latitude / Longitude, assumes some base coordinate system even if the base is not explicitly specified as is often the case with data when latitude and longitude numbers are used 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.

Illustrations -  Many classic, named projections are illustrated in the Projections Album topics.    

EPSG is not Universal -  Modern GIS software will support the use of EPSG codes, although not all packages which claim to support EPSG do so correctly.  See, for example, the discussion in the That YX Thing essay.

EPSG and WKT / WKT2 - Writing a coordinate system to WKT or WKT2 text fields (such as when using the Compose text transform) writes authority codes for EPSG systems. Parsing a coordinate system from WKT or WKT2 text fields (such as when using the Copy text transform with wkt geometry in the Use parameter)  reads authority codes for EPSG systems and, if the definition of the parsed system matches that of the referenced EPSG system, adds the EPSG code to the parsed system.  That allows using transforms for that system specified in the EPSG database, such as transforms based on grid files.

List all units of measure - Transform templates often provide parameter boxes that have a list of all available units of measure, and coordinate system dialogs often do as well.  However, if we would like a list of all units of measure available we can use SQL:

TABLE CALL CoordUnits();

or more elegantly, with a field that indicates if the unit of measure is an angular unit suitable for latitude/longitude coordinate systems:

SELECT

  StringJsonValue([value], 'Unit', true) AS [name],

  Coalesce(StringJsonBoolean([value], 'UnitLatLon', true), false) AS [latlon]

FROM CALL CoordUnits();

See Also

Info Pane: Component

Coordinates

Enhanced Accuracy

Projections

Assign Initial Coordinate System

Reproject Component

Sub-pixel Reprojection

Map Projection

Coordinate System Metrics

Unit Converter

Base Coordinate System

Favorite Coordinate Systems

Favorite Base Coordinate Systems

Example: Convert a 0 to 360 Degree Projection - We often encounter data, both images and drawings, using latitude and longitude degrees that appears to be in Latitude / Longitude projection but which has longitude values from 0 degrees to 360 degrees and latitude values from 0 degrees to 180 degrees, instead of the usual arrangement of -180 degrees to 180 degrees for longitude centered on the Prime Meridian, and -90 degrees to 90 degrees for latitude centered on the Equator.  This example shows how to utilize such data by assigning the correct projection.

Example: Assign Initial Coordinate System - Use the Component tab of the Info 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 Reproject Component 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.

Reprojection 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