Title: Extract Coordinate System Metadata
Version: 0.3.0
Description: Obtain coordinate system metadata from various data formats. There are functions to extract a 'CRS' (coordinate reference system, https://en.wikipedia.org/wiki/Spatial_reference_system) in 'EPSG' (European Petroleum Survey Group, http://www.epsg.org/), 'PROJ4' https://proj.org/, or 'WKT2' (Well-Known Text 2, http://docs.opengeospatial.org/is/12-063r5/12-063r5.html) forms. This is purely for getting simple metadata from in-memory formats, please use other tools for out of memory data sources.
License: GPL-3
Encoding: UTF-8
LazyData: true
RoxygenNote: 7.1.0
Depends: R (≥ 3.5.0)
Suggests: testthat (≥ 2.1.0), spelling
Imports: methods
URL: https://github.com/hypertidy/crsmeta
BugReports: https://github.com/hypertidy/crsmeta/issues
Language: en-US
NeedsCompilation: no
Packaged: 2020-03-29 09:58:44 UTC; mdsumner
Author: Michael Sumner ORCID iD [aut, cre]
Maintainer: Michael Sumner <mdsumner@gmail.com>
Repository: CRAN
Date/Publication: 2020-03-29 10:10:02 UTC

crsmeta: Extract Coordinate System Metadata

Description

Obtain coordinate system metadata from various data formats. There are functions to extract a 'CRS' (coordinate reference system, <https://en.wikipedia.org/wiki/Spatial_reference_system>) in 'EPSG' (European Petroleum Survey Group, <http://www.epsg.org/>), 'PROJ4' <https://proj.org/>, or 'WKT2' (Well-Known Text 2, <http://docs.opengeospatial.org/is/12-063r5/12-063r5.html>) forms. This is purely for getting simple metadata from in-memory formats, please use other tools for out of memory data sources.

Obtain coordinate system metadata from various in-memory R formats.

Details

Coordinate reference systems (CRS) are described at https://en.wikipedia.org/wiki/Spatial_reference_system. The European Petroleum Survey Group (EPSG) codes are maintained at http://www.epsg.org/. The old 'PROJ4' forms (along with newer systems) are described with the 'PROJ' library https://proj.org/. The Well-Known Text system 'WKT2' is documented at http://docs.opengeospatial.org/is/12-063r5/12-063r5.html.

There are a few functions to return a character string of length one of each main kind of projection string.

crs_epsg short numeric EPSG lookup
crs_proj short PROJ4 style string
crs_wkt2 the full parameter set as WKT2 string

Note, this help page has a weird name because for some reason 'crsmeta-package' prevents the page showing up in pkgdown docs.

Author(s)

Maintainer: Michael Sumner mdsumner@gmail.com (ORCID)

See Also

Useful links:

Extract 'EPSG' value

Description

Obtain the 'EPSG' string from an object, if it has one. Supported inputs include sf.

Usage

crs_epsg(x, ...)

Arguments

x

object with 'EPSG' value

...

ignored

Value

integer (or NA)

References

EPSG website

See Also

crs_wkt2() crs_proj() crs_input()

Examples

crs_epsg(sfx)
x <- sfx
attr(x$geom, "crs")$epsg <- NA ## oh no we lost it
crs_epsg(x)

crs_epsg(sfx_new) ## NA, doesn't exist now

Extract 'input' value

Description

Obtain the 'input' string from an object, if it has one. Supported inputs include sf (>= 0.8-1 - probably).

Usage

crs_input(x, ...)

Arguments

x

object with 'input' value

...

ignored

Value

character (or NA)

Warning

Note that the 'input' value could be almost anything, there is a huge variety of inputs that can work such as 4326, projstrings, WKT2 strings, EPSG declarations 'EPSG:4326', or common strings like 'WGS84' or 'NAD27'.

Strings like '+init=epsg:4326' have been deprecated but still can work, so beware.

References

sf

See Also

crs_wkt2() crs_proj() crs_epsg()

Examples

crs_input(sfx) ## doesn't have one

crs_input(sfx_new)  ## a proj4string

Extract 'PROJ4' string

Description

Obtain the 'PROJ4' string from an object, if it has one. Supported inputs include raster, sf, sp, and silicate.

Usage

crs_proj(x, ...)

Arguments

x

object with 'PROJ4' string

...

ignored

Value

character string (or NA)

References

PROJ system website

See Also

crs_epsg() crs_wkt2() crs_input()

Examples

crs_proj(sfx)

crs_proj(sfx$geom)

crs_proj(sfx_new) ## NA

Extract 'WKT2' string

Description

Obtain the 'WKT2' string from an object, if it has one. Supported inputs include sp and sf.

Usage

crs_wkt2(x, ...)

crs_wkt(x, ...)

Arguments

x

object with 'WKT2' string

...

ignored

Details

The functions crs_wkt() and crs_wkt2() are aliased, they do the same thing.

Value

character string (or NA)

Warning

For WKT2 only, PROJ6 and beyond

References

WKT2 specification

See Also

crs_epsg() crs_proj() crs_wkt() crs_input()

Examples

crs_wkt2(sfx) # NA
crs_wkt2(sfx$geom) # NA

crs_wkt2(sfx_new)
crs_wkt2(sfx_new$geom)

Simple features example data

Description

A copy of the 'minimal_mesh' data set from the silicate package, with coordinate reference system information added.

Details

sfx is the old-style PROJ.4 and EPSG code CRS (prior to sf 0.8-1).

sfx_new is the new-style WKT2, with user input.

Warning

do not use this data in real situations, or as exemplary of the 'sf' format. It was created purely to add examples to this package.

Examples

## three equivalent representations, of increasing richness
crs_epsg(sfx)

crs_proj(sfx)

crs_wkt2(sfx)  ## did not exist in earlier sf

## new style
crs_epsg(sfx_new) ## NA!
crs_proj(sfx_new) ## NA!

crs_input(sfx_new)
crs_wkt(sfx_new)