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Geoscience > Main Launcher > Project Menu > Properties > Coordinate Systems > Detailed Coordinate System Parameters

Detailed Coordinate System Parameters

This Detailed Coordinate System Parameters dialog displays detailed information about the currently selected coordinate system.

 

Coordinate System

This section displays basic information about the coordinate system.

Name: The name of the currently selected coordinate system.

EPSG Number: This is the official EPSG (European Petroleum Survey Group) number defining the coordinate system. Coordinate systems are based on a table of coordinate systems published by the EPSG. Note: If this field is blank it means that this is a custom coordinate system.

Units:  These are the default surface units for the selected coordinate system. Note: If the Units are missing this is likely a geographical rather than a projected coordinate system.

Surface Units:  The surface units being used for the coordinate system. Typically this will be the same as the Units value, but you can override this selection in the main dialog to work in units other than the predefined coordinate system units.

Projection Parameters

This section displays information detailing how latitude/longitude data is projected onto the map. Note: If there are no parameters in this section this is likely a geographical rather than a projected coordinate system. Use of geographical coordinate systems is not recommended within the software.

Projection Method: The method of projecting latitude/longitude data onto the map. We support the following projection methods.

Projection Parameters

The following is a complete list of possible projection parameters for various projection methods.

Natural Origin Latitude: The latitude of the point of the central reference for the coordinate system.

Natural Origin Longitude: The longitude of the point of the central reference for the coordinate system. This is often referred to as the central meridian.

Natural Origin Scale: A scale factor applied to produce the projected grid. This scale factor is defined at the natural origin.

False Easting: The projected value in the X direction defined at the origin longitude. This is typically a large value such as 500,000 which is used to avoid having to deal with negative projected values.

False Northing: The projected value in the Y direction defined at the origin latitude. This value will typically be zero.

First Parallel Latitude: Used with conic projections, this is he latitude of the one of the parallels that intersects the cone with the ellipsoid.

Second Parallel Latitude: Used with conic projections, this is he latitude of the one of the parallels that intersects the cone with the ellipsoid.

False Origin Latitude: The latitude at the point that the False Origin Easting and False Origin Northing are defined.

False Origin Longitude: The longitude at the point that the False Origin Easting and False Origin Northing are defined.

False Origin Easting: The projected value in the X direction defined at the intersection of the False Origin Latitude and False Origin Longitude.

False Origin Northing: The projected value in the Y direction defined at the intersection of the False Origin Latitude and False Origin Longitude.

Projection Center Latitude: The latitude of the point at which the Initial Line Azimuth is defined.

Projection Center Longitude: The longitude of the point at which the Initial Line Azimuth is defined.

Initial Line Azimuth: The angular direction of the center line for an oblique projection.

Rectified to Skew Angle: The angle the projection is rotated to point to true north.

Initial Line Scale: A scale factor applied to produce the projected grid. The scale factor is defined at the intersection of the Projection Center Latitude and Projection Center Longitude.

Projection Center Easting: The projected value in the X direction defined at the intersection of the Projection Center Latitude and Projection Center Longitude.

Projection Center Northing: The projected value in the Y direction defined at the intersection of the Projection Center Latitude and Projection Center Longitude.


Geographic Coordinate System

This section displays information about the geographic coordinate system. The geographic coordinate system is the earth model that represents locations on the earth in latitudes and longitudes.

Name: The name of the geographic coordinate system. If this is an EPSG coordinate system this will be the EPSG name.

Datum Name: The name of the geodetic datum for the geographic coordinate system. The geodetic datum is the reference model of the earth that the coordinate system is based on. If this is an EPSG coordinate system the name will be the EPSG name.

Ellipsoid

This section displays information about the ellipsoid of the coordinate system. The ellipsoid is a mathematical model of the  shape of the earth that approximates the actual shape of the earth. The ellipsoid is sometimes referred to as the spheroid.

Name: The name of the ellipsoid. If this is an EPSG coordinate system this will be the EPSG name of the ellipsoid.

Semi-major Axis: The semi-major axis is the radius of the earth at the equator used for this ellipsoid. It is defined as one half of the largest diameter of the earth at the equator.

Semi-minor Axis: The semi-minor axis is the radius of the earth through the north and south pole for this ellipsoid. It is defined as one half of the largest diameter of the earth running through the poles. Note: Only one of the parameters Semi-minor Axis and Inverse Flattening are typically defined as one can be derived from the other.

Inverse Flattening: A measure of the flattening of the ellipsoid's poles toward the equator. It is an inverse ratio (1 / f) represented by the flattening formula f = ((a - b) / a) where a is the semi-major axis and b is the semi-minor axis. Note: Only one of the parameters Semi-minor Axis and Inverse Flattening are typically defined as one can be derived from the other.

Axis Units: These are the units of measure for the semi-major and semi-minor axes. This will typically be meters.


Prime Meridian

This section displays information about the prime meridian of the coordinate system. The prime meridian is the line of longitude for the coordinate system defined to be zero degrees.

Name: The name of the prime meridian. If this is an EPSG coordinate system this will be the EPSG name of the prime meridian.

Offset to Greenwich: The offset in decimal degrees of the prime meridian to the Greenwich Meridian (also known as the International Meridian). This parameter is used to convert data between different coordinate systems.

WGS 84 Transformation

This section displays information about datum shifts which are applied when converting between different coordinate systems. A datum shift is the difference between the same coordinate in two different coordinate systems. Because datum shifts can vary from place to place within a coordinate system it is common to specify a custom datum shift that represents the specific area you are interested in. The datum shift in this dialog is used to specify the shift that needs to be applied to place a location in the same spot as in the WGS 84 (World Geodetic System 84) coordinate system. All datum shifts between different coordinate systems are performed relative to the reference coordinate system WGS 84. You will specify either the three X,Y and Z shift parameters or all seven parameters depending on the datum shift method used.

X Shift: Specifies the datum shift in the X (typically east/west) direction needed to transform a point to the equivalent position in the WGS 84 coordinate system. This shift is always specified in meters.

Y Shift: Specifies the datum shift in the Y direction (typically north/south) needed to transform a point to the equivalent position in the WGS 84 coordinate system. This shift is always specified in meters.

Z Shift: Specifies the datum shift in the Z (elevation) direction needed to transform a point to the equivalent position in the WGS 84 coordinate system. This shift is always specified in meters.

X Rotation: Specifies a rotation factor applied in the X direction. This is specified in seconds of arc.

Y Rotation: Specifies a rotation factor applied in the Y direction. This is specified in seconds of arc.

Z Rotation: Specifies a rotation factor applied in the Z direction. This is specified in seconds of arc.

Scale Difference: Scaling factor applied to the transformation. The scaling factor is specified in parts per million.



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