WL#10416: Ellipsoidal ST_Length

Affects: Server-8.0   —   Status: Complete   —   Priority: Medium

ST_Length currently only supports computations in Cartesian spatial reference systems (SRSs). This WL extends ST_Length to detect that its parameter is in a geographic (ellipsoidal) SRS and to compute the length on the ellipsoid.

Projected SRSs and SRID 0 will still return the same result as before. If the SRID refers to a geographic SRS, the result will be different.

F-1
ST_Length MUST return NULL if its argument is NULL.
F-2
If the argument is not a syntactically well-formed geometry, ST_Length MUST raise ER_GIS_INVALID_DATA during function evaluation.
F-3
ST_Length MUST return NULL if its argument is a geometry that is not a linestring or a multilinestring.
F-4
ST_Length MUST NOT return NULL if the parameter is a linestring or a multilinestring.
F-5
If the argument is in an undefined SRS, ST_Length MUST raise ER_SRS_NOT_FOUND during function evaluation.
F-6
If the argument is geometrically invalid, ST_Length MUST either return a length result or raise an error. If a length is returned, the value is undefined, i.e., it may be any number.
F-7
If the argument is a valid linestring in a Cartesian SRS, ST_Length MUST return the Cartesian length of the linestring.
F-8
If the argument is a valid multilinestring in a Cartesian SRS, ST_Length MUST return the sum of the Cartesian length of the linestrings.
F-9
If the argument is a valid linestring in a geographic SRS, ST_Length MUST return the geodetic length of the linestring in that SRS. The result MUST be in meters.
F-10
If the argument is a valid multilinestring in a geographic SRS, ST_Length MUST return the sum of the geodetic length of the linestrings in that SRS. The result MUST be in meters.
F-11
If a length computation results in +Inf, ST_Length MUST raise ER_DATA_OUT_OF_RANGE during function evaluation.
F-12
If the argument is a geometry in a geographic SRS and a longitude value is not in the range (-180,180] (in degrees -- other limits in other units), ST_Length MUST raise ER_LONGITUDE_OUT_OF_RANGE.(*)
F-13
If the argument is a geometry in a geographic SRS and a latitude value is not in the range [-90,90] (in degrees -- other limits in other units), ST_Length MUST raise ER_LATITUDE_OUT_OF_RANGE.(*)

(*) The exact limits will deviate slightly because of floating point arithmetics.

I-1
No new files.
I-2
No new syntax.
I-3
No new commands.
I-4
No new tools.
I-5
The semantics of interface SQL01 are changed: If the linestring is in a geographic SRS, ST_Length will return the geodetic length of the the linestring, or raise an error if the coordinates are out of bounds. Other calculations will remain as they are today.
I-6
No new errors or warnings.
  • See WL#9347 for an example of how to implement geography support. Follow the same pattern.
  • Rename the item from Item_func_glength to Item_func_st_length.
  • Make sure resolve_type() sets maybe_null correctly.
  • Re-implement val_real() based on the pattern from Item_func_distance::val_real().