| <!-- |
| Licensed to the Apache Software Foundation (ASF) under one |
| or more contributor license agreements. See the NOTICE file |
| distributed with this work for additional information |
| regarding copyright ownership. The ASF licenses this file |
| to you under the Apache License, Version 2.0 (the |
| "License"); you may not use this file except in compliance |
| with the License. You may obtain a copy of the License at |
| |
| http://www.apache.org/licenses/LICENSE-2.0 |
| |
| Unless required by applicable law or agreed to in writing, |
| software distributed under the License is distributed on an |
| "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY |
| KIND, either express or implied. See the License for the |
| specific language governing permissions and limitations |
| under the License. |
| --> |
| |
| # ST_Length |
| |
| Introduction: Returns the spherical length of a geography in meters, calculated on the sphere. The Earth is modeled as a sphere of radius `R = 6 371 008 m` (the mean Earth radius). Each edge between successive vertices is interpreted as a great-circle arc; the per-edge arc-angles are summed and scaled by `R`. |
| |
| Multi-linestrings sum the children's lengths; geography collections recurse and add up the lengths of their linear members. Returns `0.0` for non-linear geographies (points, polygons) and for `NULL`. |
| |
|  |
| |
| If you specifically want the WGS84 ellipsoidal length (which differs from the spherical value by up to ~0.5 % depending on latitude), convert via `ST_GeogToGeometry` first and call the Geometry-typed `ST_Length(..., useSpheroid => true)` overload instead. |
| |
| Format: |
| |
| `ST_Length (A: Geography)` |
| |
| Return type: `Double` |
| |
| Since: `v1.9.1` |
| |
| SQL Example |
| |
| ```sql |
| SELECT ST_Length(ST_GeogFromWKT('LINESTRING (0 0, 1 0)')); |
| ``` |
| |
| Output (in meters): |
| |
| ``` |
| 111195.10117748393 |
| ``` |
| |
| The result is approximately 111.2 km — one degree of arc on a sphere of radius `R = 6 371 008 m`. |
