Adding a coustom point as new node to an existing (Multi)Polygon or (Multi)LineString

[HansGIS]

Hello,

I was trying to find a way how to add a custom point as new node to an existing (Multi)Polygon or (Multi)LineString.

Googling did not bring me further to a solution.
The only relevant finding was Adding Nodes to Linestrings at Overlapping Points with Polygon Layer in Spatialite on stackexchange. Maybe I missed something.

The original Problem I'm trying to solve is illustrated in the example sketch below. I'd like to add node 5 to Polygon 1 between node 1 and and node 2 so I can dissolve Polygon 1 and 2 with ST_Union(). This Process is supposed to work between two (Multi)Polygons or two (Multi)LineStrings.

Any helpful hint is much appreciated.

[a.fu...@lqt.it]

On Fri, 25 Nov 2016 05:37:47 -0800 (PST), HansGIS wrote:
> Hello,
>
> I was trying to find a way how to add a custom point as new node to
> an
> existing (Multi)Polygon or (Multi)LineString.
>

you can simply use ST_AddPoint()

http://www.gaia-gis.it/gaia-sins/spatialite-sql-4.3.0.html#p7

caveat: this function accepts a single LineString or Ring, so
you must extract first (and then replace) the appropriate
Linesstring or Ring from within your complex (Multi)Polygon
or (Multi)Linestring.

bye Sandro

[mj10777]

INSERT INTO  create_cutline_linestrings  (name, cutline_linestring)

SELECT

 "Shortest Line between 'Big Polygon' and point 2 of 'Small Polygon",

 ST_ShortestLine

 (

   (SELECT cutline_polygon FROM create_cutline_polygons WHERE (name="Big Polygon")), 
   -- point 2 of the "Small Polygon" corresponds to your point 5 of Polygon 2

   (SELECT ST_PointN(ST_ExteriorRing(cutline_polygon),2) FROM create_cutline_polygons WHERE (name="Small Polygon"))

 ) AS shorestline

;

INSERT INTO  create_cutline_points  (name, cutline_point)

SELECT

 "First point of Shortest Line on 'Big Polygon' from 'Small Polygon",

  (SELECT ST_PointN(cutline_linestring,1) FROM create_cutline_linestrings WHERE (name="Shortest Line between 'Big Polygon' and point 2 of 'Small Polygon")) AS first_point

;