12.16.7.3 LineString and MultiLineString Property Functions (original) (raw)

12.16.7.3 LineString and MultiLineString Property Functions

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

Some functions in this section also work forMultiLineString values.

• EndPoint(ls)
  ST_EndPoint() andEndPoint() are synonyms. For more information, see the description ofST_EndPoint().
  EndPoint() is deprecated; expect it to be removed in a future MySQL release. UseST_EndPoint() instead.
• GLength(ls)
  GLength() is a nonstandard name. It corresponds to the OpenGISST_Length() function. (There is an existing SQL functionLength() that calculates the length of string values.)
  GLength() is deprecated; expect it to be removed in a future MySQL release. UseST_Length() instead.
• IsClosed(ls)
  ST_IsClosed() andIsClosed() are synonyms. For more information, see the description ofST_IsClosed().
  IsClosed() is deprecated; expect it to be removed in a future MySQL release. UseST_IsClosed() instead.
• NumPoints(ls)
  ST_NumPoints() andNumPoints() are synonyms. For more information, see the description ofST_NumPoints().
  NumPoints() is deprecated; expect it to be removed in a future MySQL release. UseST_NumPoints() instead.
• PointN(ls,N)
  ST_PointN() andPointN() are synonyms. For more information, see the description ofST_PointN().
  PointN() is deprecated; expect it to be removed in a future MySQL release. UseST_PointN() instead.
• ST_EndPoint(ls)
  Returns the Point that is the endpoint of the LineString value_ls_. If the argument isNULL or an empty geometry, the return value is NULL.

mysql> SET @ls = 'LineString(1 1,2 2,3 3)';  
mysql> SELECT ST_AsText(ST_EndPoint(ST_GeomFromText(@ls)));  
+----------------------------------------------+  
| ST_AsText(ST_EndPoint(ST_GeomFromText(@ls))) |  
+----------------------------------------------+  
| POINT(3 3)                                   |  
+----------------------------------------------+  

ST_EndPoint() andEndPoint() are synonyms.

• ST_IsClosed(ls)
  For a LineString value_ls,ST_IsClosed() returns 1 ifls_ is closed (that is, itsST_StartPoint() andST_EndPoint() values are the same). If the argument is NULL or an empty geometry, the return value is NULL.
  For a MultiLineString value_ls,ST_IsClosed() returns 1 ifls_ is closed (that is, theST_StartPoint() andST_EndPoint() values are the same for each LineString in_ls).
  ST_IsClosed() returns 0 ifls_ is not closed.

mysql> SET @ls1 = 'LineString(1 1,2 2,3 3,2 2)';  
mysql> SET @ls2 = 'LineString(1 1,2 2,3 3,1 1)';  
mysql> SELECT ST_IsClosed(ST_GeomFromText(@ls1));  
+------------------------------------+  
| ST_IsClosed(ST_GeomFromText(@ls1)) |  
+------------------------------------+  
|                                  0 |  
+------------------------------------+  
mysql> SELECT ST_IsClosed(ST_GeomFromText(@ls2));  
+------------------------------------+  
| ST_IsClosed(ST_GeomFromText(@ls2)) |  
+------------------------------------+  
|                                  1 |  
+------------------------------------+  
mysql> SET @ls3 = 'MultiLineString((1 1,2 2,3 3),(4 4,5 5))';  
mysql> SELECT ST_IsClosed(ST_GeomFromText(@ls3));  
+------------------------------------+  
| ST_IsClosed(ST_GeomFromText(@ls3)) |  
+------------------------------------+  
|                                  0 |  
+------------------------------------+  

ST_IsClosed() andIsClosed() are synonyms.

• ST_Length(ls)
  Returns a double-precision number indicating the length of the LineString orMultiLineString value_ls_ in its associated spatial reference system. The length of aMultiLineString value is equal to the sum of the lengths of its elements. If the argument isNULL or an empty geometry, the return value is NULL.

mysql> SET @ls = 'LineString(1 1,2 2,3 3)';  
mysql> SELECT ST_Length(ST_GeomFromText(@ls));  
+---------------------------------+  
| ST_Length(ST_GeomFromText(@ls)) |  
+---------------------------------+  
|              2.8284271247461903 |  
+---------------------------------+  
mysql> SET @mls = 'MultiLineString((1 1,2 2,3 3),(4 4,5 5))';  
mysql> SELECT ST_Length(ST_GeomFromText(@mls));  
+----------------------------------+  
| ST_Length(ST_GeomFromText(@mls)) |  
+----------------------------------+  
|                4.242640687119286 |  
+----------------------------------+  

ST_Length() should be used in preference to GLength(), which has a nonstandard name.

• ST_NumPoints(ls)
  Returns the number of Point objects in the LineString value_ls_. If the argument isNULL or an empty geometry, the return value is NULL.

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

ST_NumPoints() andNumPoints() are synonyms.

• ST_PointN(ls,N)
  Returns the N-thPoint in theLinestring valuels. Points are numbered beginning with 1. If any argument is NULL or the geometry argument is an empty geometry, the return value isNULL.

mysql> SET @ls = 'LineString(1 1,2 2,3 3)';  
mysql> SELECT ST_AsText(ST_PointN(ST_GeomFromText(@ls),2));  
+----------------------------------------------+  
| ST_AsText(ST_PointN(ST_GeomFromText(@ls),2)) |  
+----------------------------------------------+  
| POINT(2 2)                                   |  
+----------------------------------------------+  

ST_PointN() andPointN() are synonyms.

• ST_StartPoint(ls)
  Returns the Point that is the start point of the LineString value_ls_. If the argument isNULL or an empty geometry, the return value is NULL.

mysql> SET @ls = 'LineString(1 1,2 2,3 3)';  
mysql> SELECT ST_AsText(ST_StartPoint(ST_GeomFromText(@ls)));  
+------------------------------------------------+  
| ST_AsText(ST_StartPoint(ST_GeomFromText(@ls))) |  
+------------------------------------------------+  
| POINT(1 1)                                     |  
+------------------------------------------------+  

ST_StartPoint() andStartPoint() are synonyms.

• StartPoint(ls)
  ST_StartPoint() andStartPoint() are synonyms. For more information, see the description ofST_StartPoint().
  StartPoint() is deprecated; expect it to be removed in a future MySQL release. UseST_StartPoint() instead.