How to create RGeo polygon in Ruby from WKT when the polygon has errors

Question

I'm working with a MySQL database with polygons stored in WKT format. Many polygons in the database have duplicate points (e.g. in the below example, the point -122.323502 47.600959 is repeated three times).

When attempting to call RGeo::Cartesian::Factory.parse_wkt() on these polygons, the result is nil.

How can I create RGeo objects from these polygons, without modifying the polygon data.

poly = "MULTIPOLYGON(((-122.362163 47.618641,-122.344621 47.592555,-122.332017 47.592458,-122.32748 47.59241,-122.326109 47.592652,-122.324738 47.592895,-122.323147 47.593478,-122.321412 47.59411,-122.320826 47.594984,-122.320669 47.596296,-122.321149 47.598627,-122.323502 47.600959,-122.323502 47.600959,-122.323502 47.600959,-122.324071 47.601688,-122.320757 47.601688,-122.32073 47.604262,-122.320767 47.607663,-122.320746 47.609703,-122.320723 47.611938,-122.320714 47.612812,-122.320772 47.614075,-122.320799 47.618495,-122.362163 47.618641)))"

parsed_poly = RGeo::Cartesian::Factory.new().parse_wkt(poly)

=>nil

"Cartesian" means x/y ("flat-earth", euclidean) coordinates. You're passing in geographic coordinates ("curved-earth", elliptical). You're using the wrong factory. — boulder_ruby, Jul 05 '15 at 01:44

boulder_ruby · Answer 1 · 2015-07-05T01:42:22.460

9

Try this:

RGeo::Geos.factory(:srid => 4326).parse_wkt(wkt_string)

edited Jul 05 '15 at 01:42

answered Aug 31 '13 at 06:23

boulder_ruby

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I know there's also `RGeo::Geographic.spherical_factory(:srid => 4326)` but I dont know enough about RGeo to be 100% sure there's a difference. – daybreaker Apr 19 '16 at 18:43

score 1 · Answer 2 · edited Sep 22 '18 at 00:02

polygon = RGeo::Geographic.spherical_factory.parse_wkt(params[:polygon])

works for me! I am using rails + mysql

First I tried to create the place record in Rails like this:

@place = Place.new(params)

Btw, my place table is like this:

`polygon` polygon DEFAULT NULL,
`latlon` point DEFAULT NULL,

So first I tried to do everything in Model and hope rgeo will automatically change polygon and latlon from text to geometry and save in mysql like a charm. And It did work at latlon as it is a Point Type. Here is what I add to place.rb

self.rgeo_factory_generator = RGeo::Geos.method(:factory)
set_rgeo_factory_for_column(:latlon, RGeo::Geographic.spherical_factory)
set_rgeo_factory_for_column(:polygon, RGeo::Geographic.spherical_factory)

Unfortunately, Polygon type does not work.

And I found this on rgeo/reographic/interface.rb

This implementation does not implement some of the more advanced geometric operations. In particular:

Relational operators such as Feature::Geometry#intersects? are not implemented for most types.

Relational constructors such as Feature::Geometry#union are not implemented for most types.

Buffer, convex hull, and envelope calculations are not implemented for most types. Boundaries are available except for GeometryCollection.

Length calculations are available, but areas are not. Distances are available only between points.

Equality and simplicity evaluation are implemented for some but not all types.

Assertions for polygons and multipolygons are not implemented.

OK. So I need to do it myself. I tried the following but not work.

polygon = RGeo::Geographic.spherical_factory.parse_wkt(params[:polygon])
params[:polygon] = polygon
@place = Place.new(place_params)
@place.save

But this worked!

polygon = RGeo::Geographic.spherical_factory.parse_wkt(params[:polygon])
@place.polygon = polygon
@place.save

I think maybe ActiveRecord cannot deal with both other type and polygon object at the same time!

How to create RGeo polygon in Ruby from WKT when the polygon has errors

2 Answers2