# STLineInterpolatePoint

STLineInterpolatePoint — Returns point geometry at supplied fraction along linestring.

Function Specification

```Function [\$(lrsowner)].[STLineInterpolatePoint] (
@p_linestring geometry,
@p_fraction   Float
@p_round_xy   int   = 3,
@p_round_zm   int   = 2
)
Returns geometry
```

Description

Given a fraction between 0 and 1.0, this function returns a geometry point at the position described by that ratio.

Ratio is combined with length, so @p_ratio of 1.0 is equivalent to @p_linestring.STLength() ie @p_linestring.STEndPoint().
For example, @p_ratio value of 0.5 returns point at exact midpoint of linestring (ct centroid).

Supports measured and unmeasured linestrings.

Supports LineStrings with CircularString elements.

Notes

Wrapper over lrs.STFindPointByRatio

Implements PostGIS ST_LineInterpolatePoint function.

Parameters

```    @p_linestring (geometry) - Linestring (including CircularString) geometry.
@p_ratio         (float) - Length ratio between 0.0 and 1.0. If Null, @p_linestring is returned.
@p_round_xy        (int) - Decimal degrees of precision to which calculated XY ordinates are rounded.
@p_round_zm        (int) - Decimal degrees of precision to which calculated ZM ordinates are rounded.
```

Result

The function calculates and returns point at provided measure/length fraction from start.

Examples

```-- Linestring
select f.fraction,
[\$(lrsowner)].[STLineInterpolatePoint] (
@p_linestring geometry::STGeomFromText('LINESTRING(-4 -4 0  1, 0  0 0  5.6, 10  0 0 15.61, 10 10 0 25.4)',0),
@p_fraction   f.fraction,
@p_round_xy   4,
@p_round_zm   3
).AsTextZM() as fPoint
from (select 0.01 * CAST(t.IntValue as numeric) as fraction
from [dbo].[Generate_Series](1,100,10) as t
) as f
order by f.fraction
GO

fraction fPoint
0.01     POINT (-3.8186 -3.8186 0 1.046)
0.11     POINT (-2.0044 -2.0044 0 1.506)
0.21     POINT (-0.1902 -0.1902 0 1.966)
0.31     POINT (2.2968 0 0 6.496)
0.41     POINT (4.8625 0 0 7.497)
0.51     POINT (7.4281 0 0 8.498)
0.61     POINT (9.9938 0 0 9.499)
0.71     POINT (10 2.5595 0 16.587)
0.81     POINT (10 5.1252 0 17.566)
0.91     POINT (10 7.6909 0 18.545)

-- Unmeasured 2D Compound curve test.
select f.fraction,
[\$(lrsowner)].[STLineInterpolatePoint] (
geometry::STGeomFromText('COMPOUNDCURVE(CIRCULARSTRING (3 6.3246, 0 7, -3 6.3246),(-3 6.3246, 0 0, 3 6.3246))',0),
f.fraction,
4,
3
).AsTextZM() as fPoint
from (select 0.01 * CAST(t.IntValue as numeric) as fraction
from [dbo].[Generate_Series](1,100,10) as t
) as f
order by f.fraction
GO

fraction fPoint
0.01     POINT (2.8163 6.4085)
0.11     POINT (0.876 6.945)
0.21     POINT (-1.1367 6.9071)
0.31     POINT (-2.9736 6.269)
0.41     POINT (-2.1079 4.4439)
0.51     POINT (-1.2421 2.6187)
0.61     POINT (-0.3764 0.7935)
0.71     POINT (0.4893 1.0316)
0.81     POINT (1.3551 2.8568)
0.91     POINT (2.2208 4.682)
```