Skip to main content

Empty MultiLineString members

View Markdown versionEdit this page on GitHub

Next version — This documentation describes a major version that is not yet the current stable release of spatial-types.

View the library roadmap

Issue #9 protects the distinction between zero line-string members, one empty member, and a mixture of empty and non-empty members. The domain tests cover XY, XYZ, XYM and XYZM in both Geometry and Geography families, using objects and coordinate arrays.

The available ISO/IEC CD 13249-3:201x(E), Committee Draft dated 2009-01-16, clause 9.4.1 defines ST_MultiLineString as a collection of ST_LineString values. Clause 5.1.57, Description 1 ar, distinguishes an empty member array from the array of supplied line strings; its <linestring text> production allows EMPTY. Clause 5.1.58 describes the corresponding nested binary representations. These references identify the supplied Committee Draft, not a final published edition or a claim of complete library conformance.

Interoperability verification​

The following default-branch revisions were checked on 2026-09-21:

ComponentCommit
spatial-writer96742f933afe9db368a177e9e1ba1afcc3fcfb33
wkt-parsercfce11754610236c8587e4a52521209ecb277834
wkb-parser86bfca8ec4e94190f5107c0dbb1b98f7ea27a2ae

The check used this issue's spatial-types implementation and the other repositories' source code through a temporary Composer autoloader. It does not assert that released Composer constraints install these revisions together. No writer or parser dependency was added to the domain library.

For each of the eight dimension/family combinations, the check constructed zero members, one empty member, and five members alternating empty and non-empty line strings. In all 24 cases:

  • WktTextStrategy produced the expected literal WKT, preserving empty member positions and the dimension qualifier.
  • WkbBinaryStrategy followed by the WKB parser preserved member count, positions and coordinates. Reconstructing the same concrete spatial type and writing it again produced identical WKB bytes.
  • The WKT parser rejected the first EMPTY token with UnexpectedValueException. This is tracked in wkt-parser #28.

Standard WKT/WKB do not carry the Geometry/Geography family or the declared reference in these adapters. The check supplied the original family and SRID 4326 when reconstructing the spatial value. It tested the writer's supported little-endian output, without adding a byte-order contract to spatial-types.

For XY values, representative output is:

MembersWKTWKB hexadecimal
NoneMULTILINESTRING EMPTY010500000000000000
One empty line stringMULTILINESTRING (EMPTY)010500000001000000010200000000000000

A mixed value produces MULTILINESTRING (EMPTY, (1 2, 3 4), EMPTY, (1 2, 3 4), EMPTY). XYZ, XYM and XYZM use the respective Z, M and ZM qualifiers and retain their own complete coordinate tuples.

The parser limitation can be reproduced independently:

$parser = new LongitudeOne\Geo\WKT\Parser();
$parser->parse('MULTILINESTRING (EMPTY)');
// UnexpectedValueException: expected an opening parenthesis, got "EMPTY".

The follow-up belongs to the current WKT parsing repository. Its implementation is separate from preserving members in the spatial domain model.