projinv
Unproject x-y map coordinates to latitude-longitude coordinates
Description
[
transforms the map coordinates specified by lat
,lon
]
= projinv(proj
,x
,y
)x
and y
in
the projected coordinate reference system specified by proj
to the
latitude-longitude coordinates lat
and lon
. Specify
proj
using a projcrs
object
(since R2020b), a map projection structure, or a GeoTIFF information
structure.
Examples
Unproject x-y Coordinates to Latitude-Longitude
Unproject x-y coordinates to latitude-longitude coordinates by specifying the projected CRS of the x-y coordinates. Then, display the latitude-longitude coordinates on geographic axes.
To do this, first import a shapefile containing the x- and y-coordinates of roads in Concord, MA. Get information about the shapefile as a structure. Find the projected CRS for the coordinates by accessing the CoordinateReferenceSystem
field of the structure.
roads = shaperead('concord_roads.shp'); x = [roads.X]; y = [roads.Y]; info = shapeinfo('concord_roads.shp'); proj = info.CoordinateReferenceSystem;
Unproject the x-y coordinates to latitude-longitude coordinates.
[lat,lon] = projinv(proj,x,y);
Display the coordinates on geographic axes.
figure geoplot(lat,lon) hold on geobasemap('streets')
The geographic CRS of the x-y coordinates used in this example is NAD83. You can find the geographic CRS that underlies a projected CRS by querying the GeographicCRS
property.
proj.GeographicCRS.Name
ans = "NAD83"
The geographic CRS underlying the 'streets'
basemap is WGS84. NAD83 and WGS84 are similar, but not identical. Therefore, at high zoom levels the coordinates and basemap may appear misaligned.
Input Arguments
proj
— Map projection
projcrs
object | scalar map projection structure | scalar GeoTIFF information structure
Map projection, specified as a projcrs
object
(since R2020b), a scalar map projection structure
(mstruct
), or a GeoTIFF information structure. For more information about
map projection structures, see defaultm
. For more information about GeoTIFF
information structures, see geotiffinfo
.
Data Types: struct
x
— Projected x-coordinates
scalar value | vector | matrix | N-D array
Projected x-coordinates, specified as a scalar value, vector, matrix,
or N-D array. The size of x
and y
must match.
Data Types: single
| double
y
— Projected y-coordinates
scalar value | vector | matrix | N-D array
Projected y-coordinates, specified as a scalar value, vector, matrix,
or N-D array. The size of x
and y
must match.
Data Types: single
| double
Output Arguments
lat
— Geodetic latitudes
scalar value | vector | matrix | N-D array
Geodetic latitudes, returned as a scalar value, vector, matrix, or N-D array, in units of degrees.
The geographic CRS of lat
matches the geographic CRS of
proj
. If proj
is a projcrs
object, then
you can find its geographic CRS by querying its GeographicCRS
property.
For example, this code shows how to create a projcrs
object from EPSG code
32610 and find the associated geographic CRS.
proj = projcrs(32610); proj.GeographicCRS.Name
ans = "WGS 84"
lon
— Geodetic longitudes
scalar value | vector | matrix | N-D array
Geodetic longitudes, returned as a scalar value, vector, matrix, or N-D array, in units of degrees.
The geographic CRS of lat
matches the geographic CRS of
proj
. If proj
is a projcrs
object, then
you can find its geographic CRS by querying its GeographicCRS
property.
For example, this code shows how to create a projcrs
object from EPSG code
32610 and find the associated geographic CRS.
proj = projcrs(32610); proj.GeographicCRS.Name
ans = "WGS 84"
Version History
Introduced before R2006aR2022b: projinv
shows improved performance on Windows with repeated use of projection
The projinv
and projfwd
functions show improved
performance on Windows® when used multiple times in the same MATLAB® session with the same projcrs
object or map projection structure
as input.
For example, this code is about 1.67 times faster than in the previous release. The code:
Gets the grid coordinates for a DTED file
Projects and unprojects the coordinates using a
projcrs
objectGets the grid coordinates for a different DTED file
Measures the time required to project and unproject the coordinates using the same
projcrs
object
function timingTest info1 = georasterinfo("n39_w106_3arc_v2.dt1"); R1 = info1.RasterReference; [latGrid1,lonGrid1] = geographicGrid(R1); p = projcrs(4088); [xfwd1,yfwd1] = projfwd(p,latGrid1,lonGrid1); [latinv1,loninv1] = projinv(p,xfwd1,yfwd1); info2 = georasterinfo("n40_w106_3arc_v2.dt1"); R2 = info2.RasterReference; [latGrid2,lonGrid2] = geographicGrid(R2); tic [xfwd2,yfwd2] = projfwd(p,latGrid2,lonGrid2); [latinv2,loninv2] = projinv(p,xfwd2,yfwd2); toc end
The approximate execution times are:
R2022a: 0.70 s
R2022b: 0.42 s
This code was timed on a Windows 10 Intel®
Xeon® CPU W-2133 @ 3.6 GHz test system, by calling the function
timingTest
.
R2020b: Unproject coordinates using projcrs
objects and additional map projection structures
Unproject coordinates by specifying a projcrs
object. A
projcrs
object enables you to transform coordinates using projection methods
not available in earlier releases, such as Hotine Oblique Mercator.
Additionally, you can unproject coordinates by specifying a map projection structure with
any valid mapprojection
field. For a list of mapprojection
field options, use the maplist
or maps
function.
See Also
Functions
Objects
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