CODEWITHSUNDEEP
rubypostgisgeosrgeo
channa ly
channa ly

Reputation: 9927

How to find the Closest point of a line string to a given location - rgeo

My point coordinates are in geographic coordinate systems. They are in memory. I need to find the nearest point on the line string to a given point using RGeo library from Ruby.

My scenario is the points are drawn in googlemap as polyline as road representation, and the location is the position of my vehicle. I need a shortest way to reach the road.

There are solutions in PostGIS but my data is in memory and I don't want to use Postgresql to serve just for this purpose.

I am checking RGeo gem but could not find any clue related to this.

[Edited]

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Ref: https://postgis.net/docs/ST_ClosestPoint.html

Upvotes: 1

Views: 713

Answers (1)

Anatolii Suhanov
Anatolii Suhanov

Reputation: 2682

It's described in details here: https://groups.google.com/forum/#!topic/rgeo-users/e1FgzpPISs8

# Create a Geos factory that uses the ffi interface
factory = RGeo::Geos.factory(:native_interface => :ffi)

# Create your polyline and point A using that ffi-backed factory.
# You can create the objects directly using the factory, or cast objects to the
# factory, whatever is the easiest way for you to get objects that are attached
# to the ffi factory.
polyline = factory.line_string( ... )
point = factory.point( ... )

# Objects that are attached to an ffi-geos factory provide access, via the
# fg_geom method, to low-level objects that understand the ffi-geos api.
# This is not really documented well, but it's a stable api that you can use.
low_level_polyline = polyline.fg_geom
low_level_point = point.fg_geom

# Now invoke the low-level libgeos calls.
# This first method, "project", gives you the distance "along" the linestring
# where it comes closest to the given point.
dist = low_level_polyline.project(low_level_point)
# This second method, "interpolate", takes a distance "along" the linestring,
# and returns the actual point on the linestring.
low_level_closest_point = low_level_polyline.interpolate(dist)

# Finally, wrap the low-level result in an RGeo point object
closest_point = factory.wrap_fg_geom(low_level_closest_point)

Upvotes: 3

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