ENVELOPE method on linestring does not return POLYGON

[yogeshsyn23]

Steps to reproduce

 factory = RGeo::Cartesian.factory
 linestring = factory.line_string([factory.point(0, 48), factory.point(0, 82)])
 envelope = linestring.envelope

 p envelope
 #<RGeo::Cartesian::LineImpl:0x2b78c "LINESTRING (0.0 48.0, 0.0 82.0)"> 

Expected behavior

Should return POLYGON.

Actual behavior

Returning LineImpl when the 2 points are on a vertical or a horizontal line

System configuration

Ruby version:
ruby 3.2.2 (2023-03-30 revision e51014f9c0) [arm64-darwin22]

OS:
MacOS Ventura Version 13.3.1

[keithdoggett]

What version of geos are you using? On 3.10 I'm seeing a polygon when I run this.

[yogeshsyn23]

I have not installed geos for this.
Correct me if i am wrong, but this method no where specifies explicit dependency on geos.
Also in the factory-compatibiltiy doc, LineString#envelope shows compatibilty with cartesian factory.

[keithdoggett]

Got it you're using the Ruby implementation. I think since Geos is now returning either NULL a point or a polygon rather than a linestring as well like in older versions we can make this change to match. I can work on a fix in the next few days.

[yogeshsyn23]

@keithdoggett is there any update to this.
also can i help in fixing this.

[keithdoggett]

I've looked into it but haven't had time to write a PR. We need to change the envelope method in RGeo::Cartesian::GeometryMethods (

rgeo/lib/rgeo/cartesian/feature_methods.rb

Lines 16 to 18 in 52d4240

	def envelope
	BoundingBox.new(factory).add(self).to_geometry
	end

) to match the definition given by Geos now.

Per Geos it can either return a polygon or a point (https://github.com/libgeos/geos/blob/a8d2ed0aba46f88f9b8987526e68eea6565d16ae/capi/geos_c.h.in#L3881-L3887), so we should just add a check for the returned geometry from the BoundingBox call and if it's a linestring, coalesce it into a polygon (probably by taking the points into an array).

i.e. something like this (haven't run this)

def envelope
        env = BoundingBox.new(factory).add(self).to_geometry
        if RGeo::Feature::LineString.check_type(env)
           boundary = factory.line_string([env.start_point, env.end_point, env.start_point, env.end_point])
           env = factory.polygon(boundary)
       end
       env
end