Subsetting: Fixes and clarifications to requirement & recommendations

standard/requirements/requirements_class_core.adoc

@@ -78,8 +78,8 @@ This resource should also match the draft https://docs.ogc.org/DRAFTS/23-058.htm
 ^|C |The content of that response SHALL be the coverage data, along with the suported self-description capabilities of the negotiated content type.
 ^|D |The response SHALL be encoded using the format(s) negotiated through the HTTP protocol.
 ^|E |If no format is negotiated, then the response SHALL be encoded using the format associated with the media type described in the link object which links to this resource, contained within the coverage (collection) resource.
-^|F |The map response SHALL be in the native (`storageCrs`) specified in the collection description, or http://www.opengis.net/def/crs/OGC/1.3/CRS84 if none is specified, unless overridden by a specific query parameter (see <<rc_crs>>).
-^|G |The headers SHALL include a `Content-Crs:` header with the URI or the safe CURIEs of the CRS used to render the map, except if the content is in the http://www.opengis.net/def/crs/OGC/1.3/CRS84 CRS.
+^|F |The coverage response SHALL be in the native (`storageCrs`) specified in the collection description, or http://www.opengis.net/def/crs/OGC/1.3/CRS84 if none is specified, unless overridden by a specific query parameter (see <<rc_crs>>).
+^|G |The headers SHALL include a `Content-Crs:` header with the URI or the safe CURIEs of the CRS of the coverage response, except if the content is in the http://www.opengis.net/def/crs/OGC/1.3/CRS84 CRS.
 ^|H |If the returned coverage has a spatial extent, the headers of the response SHALL include a `Content-Bbox:` header with the actual geospatial boundary of the coverage.
 ^|I |If applicable, the `Content-Bbox:` coordinates SHALL be in the response CRS (indicated in `Content-Crs:`, or http://www.opengis.net/def/crs/OGC/1.3/CRS84 if it is not present) and SHALL contain four comma separated numbers representing the lower-left and upper right corners of the response honoring the CRS coordinates order.
 ^|J |An implementation not supporting the <<rc-scaling, "Scaling" requirements class>> SHALL still accept a `scale-factor` query parameter for a GET operation on the coverage resource, but only for a value of exactly `1` (returning a 4xx error otherwise). In this case, the implementation will simply ignore the parameter, and either return the data at the native resolution as if the parameter was not used, or return an error if the selected subset or the whole coverage requested would exceed the server limits. This allows for clients wishing to ensure they always retrieve a native resolution coverage by always including a `scale-factor=1` parameter.

standard/requirements/requirements_class_coverage_subset.adoc

@@ -54,7 +54,7 @@ If the vertical axis is included, the third and the sixth number are the bottom
 ^|*Requirement {counter:req-id}* |*/req/subsetting/bbox-crs*
 ^|A|The coverage resource SHALL support a `bbox-crs` parameter specifying the CRS used for the `bbox` parameter.
 ^|B|For Earth centric data, the implementation SHALL support http://www.opengis.net/def/crs/OGC/1.3/CRS84 as a value.
-^|C|If the bbox-crs is not indicated http://www.opengis.net/def/crs/OGC/1.3/CRS84 SHALL be assumed.
+^|C|If the `bbox-crs` is not indicated http://www.opengis.net/def/crs/OGC/1.3/CRS84 SHALL be assumed.
 ^|D|The native CRS (`storageCrs`) SHALL be supported as a value. Other conformance classes may allow additional values (see `crs` parameter definition).
 ^|E|The CRS expressed as URIs or as safe CURIEs SHALL be supported.
 ^|F|If the bbox parameter is not used, the `bbox-crs` SHALL be ignored.
@@ -117,7 +117,8 @@ March 18, 2018, 12:31:12 UTC or earlier:
 [width="90%",cols="2,6a"]
 |===
 ^|*Requirement {counter:req-id}* |*/req/subsetting/subset*
-^|A |The operation SHALL support a parameter `subset` with the following characteristics (using an Extended Backus Naur Form (EBNF) fragment):
+^|A |The coverage request operation SHALL support a parameter `subset` to subset one or more of the dimensions of the coverage (as described in the collection information)
+with the following characteristics (using an Extended Backus Naur Form (EBNF) fragment):
 
 [source,EBNF]
 ----
@@ -134,13 +135,30 @@ March 18, 2018, 12:31:12 UTC or earlier:
      {number} is an integer or floating-point number, and
      {text} is some general ASCII text (such as a time and date notation in ISO 8601).
 ----
-^|B |The axis name SHALL correspond to one of the axis of the Coordinate Reference System (CRS) of the coverage or else return a 400 status code.
-^|C |If the _intervalOrPoint_ values fall entirely outside the range of valid values defined for the identified axis, a 204 status code SHALL be returned
-^|D |For a CRS where an axis can wrap around, such as subsetting across the dateline (anti-meridian) in a geographic CRS, a `low` value greater than `high` SHALL
-be supported to indicate an extent crossing that wrapping point.
-^|E |Only that part of the coverage that falls within the bounds of the subset expression SHALL be returned.
-^|F |If a lower limit of the subset expression is populated with an asterisk `*`, then the minimum extent of the coverage along that axis SHALL be selected.
-^|G |If a upper limit of the subset expression is populated with an asterisk `*`, then the maximum extent of the coverage along that axis SHALL be selected.
+
+^|B   |Only that part of the coverage that falls within the bounds of the subset expression SHALL be returned.
+^|C   |If a single point is provided for an axis, the coverage response SHALL be the result of a slicing operation for the dimension corresponding to that axis, reducing the dimension.
+^|D   |If an interval is provided for an axis, the coverage response SHALL be the result of a trimming operation for the dimension corresponding to that axis, preserving the dimension.
+^|E	|Axis names `Lat` and `Lon` SHALL be supported for geographic subsetting CRS and `E` and `N` for a projected subsetting CRS, which are to be interpreted as the best matching spatial axis in the subsetting CRS definition.
+^|F	|If a third spatial dimension is supported (if the resource’s spatial extent bounding box is three dimensional), the implementation SHALL also support a `h` dimension.
+      This is the elevation above the ellipsoid in EPSG:4979 or CRS84h for geographic CRS and `z` for projected CRS, which are to be interpreted as the vertical axis in the CRS definition.
+^|G	|Axis name `time` SHALL be supported if the collection describes a temporal dimension in its extent.
+^|H	|Any name of the additional dimensions in the extent of the collection SHALL be supported as axis name.
+^|I	|A 400 error status code SHALL be returned if an axis name in the subset parameter value does not correspond to one of the axes of the subsetting CRS^2^, to a `time` temporal axis,
+       or to an additional dimension described in the collection extent.
+^|J	|If the _intervalOrPoint_ values fall entirely outside the range of valid values defined for the identified axis, a 204 or 404 status code SHALL be returned.
+^|K   |For an axis that can wrap around, such as subsetting across the dateline (anti-meridian) in a geographic CRS, a `low` value greater than `high` SHALL
+       be supported to indicate an extent crossing that wrapping point.
+^|L   |For the `time` axis, coordinates SHALL be interpreted as values for the named axis of the `trs` specified in the collection's temporal extent, or Gregorian UTC time (as specified in RFC 3339) if it is not specified in the temporal extent.
+^|M   |For a spatial axis, coordinates SHALL be interpreted as values for the named axis of the CRS specified in the `subset-crs` parameter value or in https://www.opengis.net/def/crs/OGC/1.3/CRS84 (https://www.opengis.net/def/crs/OGC/1.3/CRS84h for vertical dimension) if the `subset-crs` parameter is missing.
+^|N   |If the subset parameter includes any of the dimensions corresponding to those of the `bbox` parameter, while that `bbox` parameter is also specified,
+       or if the subset parameter includes the `time` dimension while the `datetime` parameter is also specified, the server SHALL return a 400 client error.
+^|O   |If a lower limit of the subset interval is populated with an asterisk `*`, then the minimum extent of the coverage along that axis SHALL be selected.
+^|P   |If a upper limit of the subset interval is populated with an asterisk `*`, then the maximum extent of the coverage along that axis SHALL be selected.
+^|Q	|Multiple subset parameters SHALL be interpreted, as if all dimension subsetting values were provided in a single subset parameter (comma separated)^1^.
+
+|1 Example: subset=Lat(-90:90)&subset=Lon(-180:180)&subset=time("2018-02-12T23:20:52Z")&subset=atm_pressure_hpa(500) is equivalent to subset=Lat(-90:90),Lon(-180:180),time("2018-02-12T23:20:52Z"),atm_pressure_hpa(500)
+2 Note that this is only valid of the spatial dimensions. The ‘additional’ dimensions rely on the names of the extent of the collection.
 |===
 
 NOTE: When the _intervalOrPoint_ values fall partially outside of the range of valid values defined by the CRS for the identified axis,
@@ -149,6 +167,17 @@ For subsetting on the range set, and for coverage media types with no geo-refere
 If a georeferencing mechanism is available within the negotiated media type, the service could decide whether to use NO_DATA values
 or simply return the properly geo-referenced values within the domain set.
 
+[[rec_coverage_subset-crs-axis-names]]
+[width="90%",cols="2,6a"]
+|===
+^|*Recommentation {counter:per-id}* |*/rec/subsetting/subset-crs-axis-names
+^|A | The names of the axis SHOULD be the abbreviated names of the axis in the CRS definition (e.g. the ones defined in the EPSG database).
+^|B |`e` (in lowercase), `X` (lowercase/uppercase) or `Easting` (lowercase/uppercase) SHOULD be interpreted as synonymous of `E`.
+^|C |`n` (in lowercase), `Y` (lowercase/uppercase) or `Northing` (lowercase/uppercase) SHOULD be interpreted as synonymous of `N`.
+^|D |`Long` (lowercase/uppercase) or `Longitude` SHOULD be interpreted as synonymous of `Lon`.
+^|E |`Latitude` SHOULD be interpreted as synonymous of `Lat`.
+|===
+
 ==== Parameter `subset-crs`
 
 [[req_coverage_subset-subset-crs]]

standard/requirements/requirements_class_crs.adoc

@@ -35,7 +35,7 @@ A successful GET response is described in the Coverages API core class (http://w
 ^|F |If the parameter value for `crs` is not valid for requested coverage, the status code of the response SHALL be 400.
 |===
 
-NOTE: When no crs parameters are specified, please refer to the Coverages API core conformance class to know about the default crs.
+NOTE: When no `crs` parameters are specified, the default output CRS is the native (`storage CRS`), which is CRS84 if none is specified (see <<rc-core,Core requirement class>> for additional details).
 
 NOTE: A CURIE `{authority}[-{objectType}]:{id}` would map to the following OGC URI: `http://www.opengis.net/def/{objectType}/{authority}/0/{id}`. If `-{objectType}` is missing, the default object type is crs.