projcrs

Projected coordinate reference system object

Description

A projected coordinate reference system (CRS) provides information that assigns Cartesian x and y map coordinates to physical locations. Projected CRSs consist of a geographic CRS and several parameters that are used to transform coordinates to and from the geographic CRS. For more information about geographic CRSs, see geocrs.

Creation

There are several ways to create projected CRS objects, including:

• Import raster data by using readgeoraster, and then query the ProjectedCRS property of the returned raster reference object.

• Get information about a shapefile by using the shapeinfo function, and then query the CoordinateReferenceSystem field of the returned structure.

• Use the projcrs function (described here).

Syntax

p = projcrs(code)

p = projcrs(code,'Authority',authority)

p = projcrs(wkt)

Description

p = projcrs(code) creates a projected CRS object using the EPSG code specified by code.

p = projcrs(code,'Authority',authority) creates a projected CRS object using the specified code and authority.

p = projcrs(wkt) creates a projected CRS object using the well-known text (WKT) string representation specified by wkt.

Input Arguments

code — Projected CRS code

positive integer | string scalar | character vector

Projected CRS code, specified as a positive integer, string scalar, or character vector. By default, the projcrs function assumes the code argument is an EPSG code. To specify other types of codes, use the 'Authority' name-value pair.

If referring to an EPSG or ESRI code, specify this argument as a positive integer. If referring to an IGNF code, specify this argument as a string scalar or character vector.

For information on valid EPSG codes, see the EPSG home page.

authority — Authority

'EPSG' (default) | 'ESRI' | 'IGNF'

Authority, specified as 'EPSG', 'ESRI', or 'IGNF'. This argument specifies which authority the projcrs function uses to determine the properties of the created projected CRS object. If you do not specify an authority, then the projcrs function uses 'EPSG'.

wkt — Well-known text

string scalar | character vector

Well-known text (WKT), specified as a string scalar or character vector. You can specify WKT using either the WKT 1 or WKT 2 standard.

The parameters listed in the ProjectionParameters property use the WKT 2 standard, even if the argument uses the WKT 1 standard.

Properties

Name — CRS name

string scalar

This property is read-only.

CRS name, returned as a string scalar.

Data Types: string

GeographicCRS — Geographic CRS

geocrs object

This property is read-only.

Geographic CRS, returned as a geocrs object. A geographic CRS consists of a datum (including its ellipsoid), prime meridian, and angular unit of measurement.

LengthUnit — Length unit

string scalar

This property is read-only.

Length unit, returned as a string scalar. Possible values include "meter" and "U.S. survey foot".

Data Types: string

ProjectionMethod — Projection method

string scalar

This property is read-only.

Projection method, returned as a string scalar. Possible values include "Lambert Conic Conformal (2SP)" and "Transverse Mercator".

Data Types: string

ProjectionParameters — Projection parameters

ProjectionParameters object

This property is read-only.

Projection parameters, returned as a ProjectionParameters object. The parameters in a ProjectionParameters object use the WKT 2 standard, even if the supplied wkt argument uses the WKT 1 standard.

You can query individual projection parameters using dot notation. For example, create a projcrs object and access the LatitudeOfFalseOrigin parameter.

p = projcrs(26986);
p.ProjectionParameters.LatitudeOfFalseOrigin

This table describes common projection parameters, including those used by the Lambert Conformal Conic and Transverse Mercator projection methods. Different projections may have parameters other than the ones listed here.

Parameter	Description
EastingAtFalseOrigin	Easting at the false origin, returned as a number in the units specified by LengthUnit. A projected CRS often uses a false origin such that all coordinates within the CRS have positive values. The easting at the false origin is with respect to the grid origin at (0, 0).
FalseEasting	False easting, returned as a number in the units specified by LengthUnit. A projected CRS often uses a false easting to shift the y-axis of the map grid so that the x-coordinates have positive values.
FalseNorthing	False northing, returned as a number in the units specified by LengthUnit. A projected CRS often uses a false northing to shift the x-axis of the map grid so that the y-coordinates have positive values.
LatitudeOf1stStandardParallel	Latitude of the first standard parallel, returned as a number. Units are typically in degrees. Standard parallels are the parallels at which the cone or cylinder used in a conic or cylindrical projection intersects the reference spheroid.
LatitudeOf2ndStandardParallel	Latitude of the second standard parallel, returned as a number. Units are typically in degrees. Standard parallels are the parallels at which the cone or cylinder used in a conic or cylindrical projection intersects the reference spheroid.
LatitudeOfFalseOrigin	Latitude of false origin, returned as a number. A projected CRS typically uses a false origin such that all coordinates within the CRS have positive values.
LatitudeOfNaturalOrigin	Latitude of the natural origin, returned as a number. Units are typically in degrees. The natural origin is the grid origin without the shift by a false northing or easting.
LongitudeOfFalseOrigin	Longitude of false origin, returned as a number. A projected CRS typically uses a false origin such that all coordinates within the CRS have positive values.
LongitudeOfNaturalOrigin	Longitude of the natural origin, returned as a number. Units are typically in degrees. The natural origin is the grid origin without the shift by a false northing or easting.
NorthingAtFalseOrigin	Northing at the false origin, returned as a number in the units specified by LengthUnit. A projected CRS typically uses a false origin such that all coordinates within the CRS have positive values. The northing at the false origin is with respect to the grid origin at (0, 0).
ScaleFactorAtNaturalOrigin	Scale factor at natural origin, returned as a number with no units. The natural origin is the grid origin without the shift by a false northing or easting. A projected CRS typically uses a scale factor (a number close to 1) to balance out scale distortion across the area covered by the coordinate system.

Object Functions

projfwd	Project latitude-longitude coordinates to x-y map coordinates
projinv	Unproject x-y map coordinates to latitude-longitude coordinates
wktstring	Well-known text string
isequal	Compare two projcrs or geocrs objects for equivalence

Examples

Get Projected CRS from EPSG Code

Create a projected CRS object by specifying an EPSG code.

p = projcrs(5325)

p = 
  projcrs with properties:

                    Name: "ISN2004 / Lambert 2004"
           GeographicCRS: [1x1 geocrs]
        ProjectionMethod: "Lambert Conic Conformal (2SP)"
              LengthUnit: "meter"
    ProjectionParameters: [1x1 map.crs.ProjectionParameters]

Get Projected CRS from ESRI Code

Create a projected CRS object from an ESRI code by using the 'Authority' name-value pair.

p = projcrs(53026,'Authority','ESRI')

p = 
  projcrs with properties:

                    Name: "Sphere_Stereographic"
           GeographicCRS: [1x1 geocrs]
        ProjectionMethod: "Stereographic"
              LengthUnit: "meter"
    ProjectionParameters: [1x1 map.crs.ProjectionParameters]

Get Projected CRS from IGNF Code

Create a projected CRS object from an IGNF code by using the 'Authority' name-value pair. Specify the code using a string or character vector.

p = projcrs('UTM39SW84','Authority','IGNF')

p = 
  projcrs with properties:

                    Name: "WGS84 UTM SUD FUSEAU 39"
           GeographicCRS: [1x1 geocrs]
        ProjectionMethod: "Transverse Mercator"
              LengthUnit: "meter"
    ProjectionParameters: [1x1 map.crs.ProjectionParameters]

Get Projected CRS from Projection File

Import a WKT projection file as a character vector by using the fileread function. Then create a projected CRS object by specifying the vector.

wkt = fileread('MtWashington-ft.prj');
p = projcrs(wkt)

p = 
  projcrs with properties:

                    Name: "UTM Zone 19, Northern Hemisphere"
           GeographicCRS: [1x1 geocrs]
        ProjectionMethod: "Transverse Mercator"
              LengthUnit: "meter"
    ProjectionParameters: [1x1 map.crs.ProjectionParameters]

Get Projected CRS from Imported Raster Data

Import raster data as an array and a map reference object using the readgeoraster function. Then, get the projected CRS by querying the ProjectedCRS property of the reference object.

[Z,R] = readgeoraster('boston.tif');
R.ProjectedCRS

ans = 
  projcrs with properties:

                    Name: "NAD83 / Massachusetts Mainland"
           GeographicCRS: [1×1 geocrs]
        ProjectionMethod: "Lambert Conic Conformal (2SP)"
              LengthUnit: "U.S. survey foot"
    ProjectionParameters: [1×1 map.crs.ProjectionParameters]

Alternatively, return information about the same file as a RasterInfo object using the georasterinfo function. Then, get the projected CRS by querying the CoordinateReferenceSystem property of the object.

info = georasterinfo('boston.tif');
info.CoordinateReferenceSystem

ans = 
  projcrs with properties:

                    Name: "NAD83 / Massachusetts Mainland"
           GeographicCRS: [1×1 geocrs]
        ProjectionMethod: "Lambert Conic Conformal (2SP)"
              LengthUnit: "U.S. survey foot"
    ProjectionParameters: [1×1 map.crs.ProjectionParameters]

Get Projection Parameters for Projected CRS

Get projection parameters for a projected CRS by creating a projcrs object and querying its ProjectionParameters property.

p = projcrs(26986);
parameters = p.ProjectionParameters

parameters = 
  ProjectionParameters object with parameters:

            LatitudeOfFalseOrigin: 41
           LongitudeOfFalseOrigin: -71.5
    LatitudeOf1stStandardParallel: 42.6833333333333
    LatitudeOf2ndStandardParallel: 41.7166666666667
             EastingAtFalseOrigin: 200000
            NorthingAtFalseOrigin: 750000

Query individual projection parameters by using dot notation.

f = parameters.EastingAtFalseOrigin

f = 200000

Tips

When you compare two ProjectionParameters objects by using the isequal function, the function might return 0 (false), even when the parameter values are the same. Instead, compare ProjectionParameters objects by comparing the projcrs objects or by comparing the parameter values directly.

Version History

Introduced in R2020b