zarr_convention_cs: GeoZarr "cs" convention
In geozarr: GeoZarr Conventions for Geospatial Data in Zarr Stores
zarr_convention_cs R Documentation
GeoZarr "cs" convention
Description
This class implements the GeoZarr "cs" (coordinate set)
convention. The convention attaches a full coordinate system to a Zarr
array by recording, for each dimension, the axis abbreviation and
direction, one or more sets of coordinate values and their optional
cell-boundary values, and, where applicable, the parametric formula and
its terms needed to derive physical coordinates from stored index
coordinates.
The convention is registered via the following CMO:
{
"schema_url": "https://raw.githubusercontent.com/R-CF/zarr_convention_cs/main/schema.json",
"spec_url": "https://raw.githubusercontent.com/R-CF/zarr_convention_cs/main/README.md",
"uuid": "e4dbf0b7-7a00-4ce6-b23e-484292014ab4",
"name": "cs",
"description": "Coordinate set convention for Zarr arrays"
}
The cs attribute written to the array metadata has the following
structure (simplified):
{
"cs": {
"crs": [
{
"type": "compound" | "planar" | "vertical" | "temporal" | "undefined",
"description: "optional text",
"axes": {
"<dimension_name>": {
"abbreviation": "X",
"direction": "EAST",
"coordinates": [ { "unit": "degrees",
"values": { "regular": [0.0, 0.5] } } ]
}
}
}
],
"id": "Identifier of a compound CRS",
"attributes": { <optional attributes as a JSON sub-schema> }
}
}
Build a convention instance, add one or more CRS objects (each covering
one or more dimension axes), then call as_list() to retrieve everything
for inclusion as the "cs" attribute in the Zarr node metadata.
Super class
zarr::zarr_convention -> zarr_convention_cs
Active bindings
nameOptional descriptive name for the coordinate set.
cs_crsOptional top-level CRS identifier, an instance of
zarr_conv_proj.
crs(read-only) The list of CRS objects accumulated so far.
Methods
Public methods
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Inherited methods
zarr_convention_cs$new()
Create a new instance of a "cs" convention agent.
Usage
zarr_convention_cs$new()
Returns
A new instance of a "cs" convention agent.
zarr_convention_cs$add_crs()
Add a CRS object to this coordinate set. Each CRS covers one
or more axes (dimensions). Multiple calls add further CRS objects to
the array, which is necessary when the array spans domains described by
separate OGC coordinate reference systems (e.g. a horizontal CRS plus a
vertical CRS plus a temporal CRS).
Usage
zarr_convention_cs$add_crs(
axes,
type = "unknown",
id = NULL,
geolocation = NULL
)
Arguments
axesA named list of axis definitions, keyed by the dimension name
that appears in the Zarr array's dimension_names metadata. If the
argument is NULL or an empty list, the call is a no-op.
typeOptional, character string. Type of CRS, one of "compound",
"planar", "vertical", "temporal", "unknown" (default).
idOptional. An instance of zarr_conv_proj providing the formal
OGC description of the CRS.
geolocationOptional list. Geolocation grid definition for
curvilinear grids. This should only be included for CRS's that
represent a planar coordinate system.
Returns
Self, invisibly.
zarr_convention_cs$as_list()
Retrieve the cs attributes as a list.
Usage
zarr_convention_cs$as_list()
Returns
A list with the updated attributes for this convention.
zarr_convention_cs$axis()
Build an axis definition.
Usage
zarr_convention_cs$axis(coordinates, abbreviation = NULL, direction = NULL)
Arguments
coordinatesA list of coordinate-set definitions, each produced by
coordinates(). Must have at least one element.
abbreviationOptional character string. Axis abbreviation, e.g.
"X", "Y", "Z", or "T".
directionOptional character string. Direction of increasing
coordinate values taken from Table 48 of the OGC standard "Referencing
by Coordinates" (e.g. "EAST", "NORTH", "UP", "FUTURE").
Returns
A named list representing one axis entry.
zarr_convention_cs$coordinates()
Build a coordinate-set definition for use in axis().
Usage
zarr_convention_cs$coordinates(
values,
name = NULL,
unit = NULL,
boundaries = NULL,
parametric = NULL,
time = NULL,
attributes = NULL
)
Arguments
valuesA values definition produced by one of values_regular(),
values_explicit(), or values_external().
nameOptional, character string. Descriptive name for this set of
coordinates.
unitOptional, character string. Unit of measure (e.g.
"degrees_east", "m", "1").
boundariesOptional boundaries definition produced by
boundaries_regular() or values_external().
parametricOptional parametric definition produced by
parametric().
timeOptional time definition produced by time().
attributesOptional list with attributes for the coordinates.
Returns
A named list representing one coordinates entry.
zarr_convention_cs$values_regular()
Regularly-spaced coordinate values.
Usage
zarr_convention_cs$values_regular(start, increment)
Arguments
startNumeric. The coordinate value at shape index 0.
incrementNumeric. The constant spacing between successive values.
May be negative for decreasing coordinates (e.g. north-to-south
latitudes); it cannot be 0.
Returns
A values list with a regular element.
zarr_convention_cs$values_explicit()
Explicitly listed coordinate values.
Usage
zarr_convention_cs$values_explicit(values)
Arguments
valuesA vector of coordinate values. May be numeric, integer, or
character.
Returns
A values list with an explicit element.
zarr_convention_cs$values_external()
Coordinate values stored in an external array
Usage
zarr_convention_cs$values_external(node, uri)
Arguments
nodeCharacter string. Path to the 1-dimensional Zarr array
containing the coordinate values, relative to the referring node.
uriOptional character string. URI of an external store. Omit for
arrays in the same local store.
Returns
A values list with an external element.
zarr_convention_cs$boundaries_regular()
Regularly-spaced cell-boundary values.
The two values give the offset below and above the coordinate value
that define the extent of each cell, in the same unit as the
coordinates. Both offsets are expressed relative to the coordinate value
so below must be non-positive and above must be non-negative.
Usage
zarr_convention_cs$boundaries_regular(below, above)
Arguments
below, aboveNumeric. Offset from the coordinate value to
the lower and upper boundary, respectively.
Returns
A boundaries list with a regular element.
zarr_convention_cs$time()
Provides the time reference information needed to interpret
numeric coordinate values on a temporal axis.
Usage
zarr_convention_cs$time(unit, epoch, calendar = NULL)
Arguments
unitCharacter string. The time unit, e.g. "days", "hours",
"seconds".
epochCharacter string. The reference date/time in ISO 8601
format, e.g. "1970-01-01".
calendarOptional character string. The CF calendar name, e.g.
"standard", "360_day". Defaults to "proleptic_gregorian" when
omitted.
Returns
A time list.
zarr_convention_cs$parametric()
Records the CF formula name and the set of formula terms
needed to derive physical coordinates from the stored parametric index
coordinates. This object sits alongside values inside a
coordinates() call; values provides the stored parametric
coordinates (e.g. s_rho), while parametric provides the machinery
to recover the physical coordinates (e.g. depth in metres).
Usage
zarr_convention_cs$parametric(formula, terms)
Arguments
formulaCharacter string. The CF standard_name of the parametric
coordinate formula, e.g. "ocean_s_coordinate_g2".
termsA named list of formula term values. Each element must be a
values attribute object. Scalar or short constants should use
explicit coordinate values; full-length arrays should use external Zarr
arrays.
Returns
A parametric list.
geozarr documentation built on Sept. 16, 2026, 1:07 a.m.
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| zarr_convention_cs | R Documentation |
GeoZarr "cs" convention
Description
This class implements the GeoZarr "cs" (coordinate set) convention. The convention attaches a full coordinate system to a Zarr array by recording, for each dimension, the axis abbreviation and direction, one or more sets of coordinate values and their optional cell-boundary values, and, where applicable, the parametric formula and its terms needed to derive physical coordinates from stored index coordinates.
The convention is registered via the following CMO:
{
"schema_url": "https://raw.githubusercontent.com/R-CF/zarr_convention_cs/main/schema.json",
"spec_url": "https://raw.githubusercontent.com/R-CF/zarr_convention_cs/main/README.md",
"uuid": "e4dbf0b7-7a00-4ce6-b23e-484292014ab4",
"name": "cs",
"description": "Coordinate set convention for Zarr arrays"
}
The cs attribute written to the array metadata has the following
structure (simplified):
{
"cs": {
"crs": [
{
"type": "compound" | "planar" | "vertical" | "temporal" | "undefined",
"description: "optional text",
"axes": {
"<dimension_name>": {
"abbreviation": "X",
"direction": "EAST",
"coordinates": [ { "unit": "degrees",
"values": { "regular": [0.0, 0.5] } } ]
}
}
}
],
"id": "Identifier of a compound CRS",
"attributes": { <optional attributes as a JSON sub-schema> }
}
}
Build a convention instance, add one or more CRS objects (each covering
one or more dimension axes), then call as_list() to retrieve everything
for inclusion as the "cs" attribute in the Zarr node metadata.
Super class
zarr::zarr_convention -> zarr_convention_cs
Active bindings
nameOptional descriptive name for the coordinate set.
cs_crsOptional top-level CRS identifier, an instance of zarr_conv_proj.
crs(read-only) The list of CRS objects accumulated so far.
Methods
Public methods
Inherited methods
zarr_convention_cs$new()
Create a new instance of a "cs" convention agent.
Usage
zarr_convention_cs$new()
Returns
A new instance of a "cs" convention agent.
zarr_convention_cs$add_crs()
Add a CRS object to this coordinate set. Each CRS covers one or more axes (dimensions). Multiple calls add further CRS objects to the array, which is necessary when the array spans domains described by separate OGC coordinate reference systems (e.g. a horizontal CRS plus a vertical CRS plus a temporal CRS).
Usage
zarr_convention_cs$add_crs( axes, type = "unknown", id = NULL, geolocation = NULL )
Arguments
axesA named list of axis definitions, keyed by the dimension name that appears in the Zarr array's
dimension_namesmetadata. If the argument isNULLor an empty list, the call is a no-op.typeOptional, character string. Type of CRS, one of "compound", "planar", "vertical", "temporal", "unknown" (default).
idOptional. An instance of zarr_conv_proj providing the formal OGC description of the CRS.
geolocationOptional list. Geolocation grid definition for curvilinear grids. This should only be included for CRS's that represent a planar coordinate system.
Returns
Self, invisibly.
zarr_convention_cs$as_list()
Retrieve the cs attributes as a list.
Usage
zarr_convention_cs$as_list()
Returns
A list with the updated attributes for this convention.
zarr_convention_cs$axis()
Build an axis definition.
Usage
zarr_convention_cs$axis(coordinates, abbreviation = NULL, direction = NULL)
Arguments
coordinatesA list of coordinate-set definitions, each produced by
coordinates(). Must have at least one element.abbreviationOptional character string. Axis abbreviation, e.g.
"X","Y","Z", or"T".directionOptional character string. Direction of increasing coordinate values taken from Table 48 of the OGC standard "Referencing by Coordinates" (e.g.
"EAST","NORTH","UP","FUTURE").
Returns
A named list representing one axis entry.
zarr_convention_cs$coordinates()
Build a coordinate-set definition for use in axis().
Usage
zarr_convention_cs$coordinates( values, name = NULL, unit = NULL, boundaries = NULL, parametric = NULL, time = NULL, attributes = NULL )
Arguments
valuesA values definition produced by one of
values_regular(),values_explicit(), orvalues_external().nameOptional, character string. Descriptive name for this set of coordinates.
unitOptional, character string. Unit of measure (e.g.
"degrees_east","m","1").boundariesOptional boundaries definition produced by
boundaries_regular()orvalues_external().parametricOptional parametric definition produced by
parametric().timeOptional time definition produced by
time().attributesOptional list with attributes for the coordinates.
Returns
A named list representing one coordinates entry.
zarr_convention_cs$values_regular()
Regularly-spaced coordinate values.
Usage
zarr_convention_cs$values_regular(start, increment)
Arguments
startNumeric. The coordinate value at shape index 0.
incrementNumeric. The constant spacing between successive values. May be negative for decreasing coordinates (e.g. north-to-south latitudes); it cannot be 0.
Returns
A values list with a regular element.
zarr_convention_cs$values_explicit()
Explicitly listed coordinate values.
Usage
zarr_convention_cs$values_explicit(values)
Arguments
valuesA vector of coordinate values. May be numeric, integer, or character.
Returns
A values list with an explicit element.
zarr_convention_cs$values_external()
Coordinate values stored in an external array
Usage
zarr_convention_cs$values_external(node, uri)
Arguments
nodeCharacter string. Path to the 1-dimensional Zarr array containing the coordinate values, relative to the referring node.
uriOptional character string. URI of an external store. Omit for arrays in the same local store.
Returns
A values list with an external element.
zarr_convention_cs$boundaries_regular()
Regularly-spaced cell-boundary values.
The two values give the offset below and above the coordinate value
that define the extent of each cell, in the same unit as the
coordinates. Both offsets are expressed relative to the coordinate value
so below must be non-positive and above must be non-negative.
Usage
zarr_convention_cs$boundaries_regular(below, above)
Arguments
below, aboveNumeric. Offset from the coordinate value to the lower and upper boundary, respectively.
Returns
A boundaries list with a regular element.
zarr_convention_cs$time()
Provides the time reference information needed to interpret numeric coordinate values on a temporal axis.
Usage
zarr_convention_cs$time(unit, epoch, calendar = NULL)
Arguments
unitCharacter string. The time unit, e.g.
"days","hours","seconds".epochCharacter string. The reference date/time in ISO 8601 format, e.g.
"1970-01-01".calendarOptional character string. The CF calendar name, e.g.
"standard","360_day". Defaults to"proleptic_gregorian"when omitted.
Returns
A time list.
zarr_convention_cs$parametric()
Records the CF formula name and the set of formula terms
needed to derive physical coordinates from the stored parametric index
coordinates. This object sits alongside values inside a
coordinates() call; values provides the stored parametric
coordinates (e.g. s_rho), while parametric provides the machinery
to recover the physical coordinates (e.g. depth in metres).
Usage
zarr_convention_cs$parametric(formula, terms)
Arguments
formulaCharacter string. The CF
standard_nameof the parametric coordinate formula, e.g."ocean_s_coordinate_g2".termsA named list of formula term values. Each element must be a
valuesattribute object. Scalar or short constants should use explicit coordinate values; full-length arrays should use external Zarr arrays.
Returns
A parametric list.
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