LineString Functions

A LineString consists of Point values. You can extract particular points of a LineString, count the number of points that it contains, or obtain its length.

• EndPoint(ls)

  Returns the Point that is the endpoint of the LineString value ls.

  mysql> SET @ls = 'LineString(1 1,2 2,3 3)';
  mysql> SELECT AsText(EndPoint(GeomFromText(@ls)));
  +-------------------------------------+
  | AsText(EndPoint(GeomFromText(@ls))) |
  +-------------------------------------+
  | POINT(3 3) |
  +-------------------------------------+
  

• GLength(ls)

  Returns as a double-precision number the length of the LineString value ls in its associated spatial reference.

  mysql> SET @ls = 'LineString(1 1,2 2,3 3)';
  mysql> SELECT GLength(GeomFromText(@ls));
  +----------------------------+
  | GLength(GeomFromText(@ls)) |
  +----------------------------+
  | 2.8284271247462 |
  +----------------------------+
  

  GLength() is a nonstandard name. It corresponds to the OpenGIS Length() function.

• NumPoints(ls)

  Returns the number of Point objects in the LineString value ls.

  mysql> SET @ls = 'LineString(1 1,2 2,3 3)';
  mysql> SELECT NumPoints(GeomFromText(@ls));
  +------------------------------+
  | NumPoints(GeomFromText(@ls)) |
  +------------------------------+
  | 3 |
  +------------------------------+
  

• PointN(ls,N)

  Returns the N-th Point in the Linestring value ls. Points are numbered beginning with 1.

  mysql> SET @ls = 'LineString(1 1,2 2,3 3)';
  mysql> SELECT AsText(PointN(GeomFromText(@ls),2));
  +-------------------------------------+
  | AsText(PointN(GeomFromText(@ls),2)) |
  +-------------------------------------+
  | POINT(2 2) |
  +-------------------------------------+
  

• StartPoint(ls)

  Returns the Point that is the start point of the LineString value ls.

  mysql> SET @ls = 'LineString(1 1,2 2,3 3)';
  mysql> SELECT AsText(StartPoint(GeomFromText(@ls)));
  +---------------------------------------+
  | AsText(StartPoint(GeomFromText(@ls))) |
  +---------------------------------------+
  | POINT(1 1) |
  +---------------------------------------+
  

The OpenGIS specification also defines the following function, which MariaDB does not implement:

• IsRing(ls)

  Returns 1 if the LineString value ls is closed (that is, its StartPoint() and EndPoint() values are the same) and is simple (does not pass through the same point more than once). Returns 0 if ls is not a ring, and -1 if it is NULL.

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