Can not take the union of polygons generated from buffering of Points

[alex-s-gardner]

This is a pretty big issue in my workflow.. to get around it I move over to pure LibGEOS:

import GeoInterface as GI
import GeometryOps as GO
using LibGEOS

pts = GI.Point.([(0.0, 0.0), (5.0, 5.0), (10.0, 0.0), (5.0, -5.0), (0.0, 0.0)])
buffered_pts = GO.buffer(pts, .1)
buffered = reduce(GO.union, buffered_pts)

ERROR: MethodError: no method matching GeometryOpsCore.TraitTarget(::Nothing)
The type `GeometryOpsCore.TraitTarget` exists, but no method is defined for this combination of argument types when trying to construct it.

Closest candidates are:
  GeometryOpsCore.TraitTarget(::T) where T<:GeoInterface.AbstractTrait
   @ GeometryOpsCore ~/.julia/packages/GeometryOpsCore/U2GQ1/src/types/traittarget.jl:33
  GeometryOpsCore.TraitTarget(::GeoInterface.AbstractTrait...)
   @ GeometryOpsCore ~/.julia/packages/GeometryOpsCore/U2GQ1/src/types/traittarget.jl:36
  GeometryOpsCore.TraitTarget(::Type{<:GeometryOpsCore.TraitTarget{T}}) where T
   @ GeometryOpsCore ~/.julia/packages/GeometryOpsCore/U2GQ1/src/types/traittarget.jl:35
  ...

Stacktrace:
 [1] union(alg::GeometryOps.FosterHormannClipping{…}, geom_a::GeoInterface.Wrappers.Polygon{…}, geom_b::GeoInterface.Wrappers.Polygon{…}, ::Type{…}; target::Nothing, kwargs::@Kwargs{})
   @ GeometryOps ~/.julia/packages/GeometryOps/avNdd/src/methods/clipping/union.jl:38
 [2] union(geom_a::GeoInterface.Wrappers.Polygon{…}, geom_b::GeoInterface.Wrappers.Polygon{…}, ::Type{…}; target::Nothing, kwargs::@Kwargs{})
   @ GeometryOps ~/.julia/packages/GeometryOps/avNdd/src/methods/clipping/union.jl:49
 [3] union(geom_a::GeoInterface.Wrappers.Polygon{…}, geom_b::GeoInterface.Wrappers.Polygon{…}, ::Type{…})
   @ GeometryOps ~/.julia/packages/GeometryOps/avNdd/src/methods/clipping/union.jl:46
 [4] _mapreduce(f::typeof(identity), op::typeof(GeometryOps.union), ::IndexLinear, A::Vector{…})
   @ Base ./reduce.jl:437
 [5] _mapreduce_dim(f::Function, op::Function, ::Base._InitialValue, A::Vector{GeoInterface.Wrappers.Polygon{…}}, ::Colon)
   @ Base ./reducedim.jl:337
 [6] mapreduce
   @ ./reducedim.jl:329 [inlined]
 [7] reduce(op::Function, A::Vector{GeoInterface.Wrappers.Polygon{false, false, Vector{…}, Nothing, String}})
   @ Base ./reducedim.jl:378
 [8] top-level scope
   @ ~/Documents/GitHub/ItsLivePlayground.jl/src/jink.jl:7
Some type information was truncated. Use `show(err)` to see complete types.

[asinghvi17]

buffered = reduce((x, y) -> GO.union(x, y; target = GI.MultiPolygonTrait()), buffered_pts)

we'll soon get rid of this requirement in favor of an auto-choosing implementation, that can pick from polygon trait or multipolygon trait depending on the number of outputs. Then what you wrote will just work, but be a little type unstable, which is probably fine.