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Sg/area dist debug #33

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Dec 28, 2023
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1 change: 1 addition & 0 deletions .gitignore
Original file line number Diff line number Diff line change
@@ -1,2 +1,3 @@
/Manifest.toml
/docs/build/
.vscode/
66 changes: 38 additions & 28 deletions src/methods/area.jl
Original file line number Diff line number Diff line change
Expand Up @@ -44,19 +44,25 @@ for polygons.
=#

"""
area(geom)::Real
area(geom, ::Type{T} = Float64)::T

Returns the area of the geometry. This is computed slighly differently for
different geometries:
- The area of a point is always zero.
- The area of a curve is always zero.
- The area of a point/multipoint is always zero.
- The area of a curve/multicurve is always zero.
- The area of a polygon is the absolute value of the signed area.
- The area multi-polygon is the sum of the areas of all of the sub-polygons.
- The area of a geometry collection is the sum of the areas of all of the
sub-geometries.

Result will be of type T, where T is an optional argument with a default value
of Float64.
"""
area(geom) = area(GI.trait(geom), geom)
area(geom, ::Type{T} = Float64) where T <: AbstractFloat =
_area(T, GI.trait(geom), geom)

"""
signed_area(geom)::Real
signed_area(geom, ::Type{T} = Float64)::T

Returns the signed area of the geometry, based on winding order. This is
computed slighly differently for different geometries:
Expand All @@ -67,38 +73,42 @@ computed slighly differently for different geometries:
counterclockwise.
- You cannot compute the signed area of a multipolygon as it doesn't have a
meaning as each sub-polygon could have a different winding order.
"""
signed_area(geom) = signed_area(GI.trait(geom), geom)

# Points
area(::GI.PointTrait, point) = zero(typeof(GI.x(point)))

signed_area(trait::GI.PointTrait, point) = area(trait, point)
Result will be of type T, where T is an optional argument with a default value
of Float64.
"""
signed_area(geom, ::Type{T} = Float64) where T <: AbstractFloat =
_signed_area(T, GI.trait(geom), geom)

# Curves
area(::CT, curve) where CT <: GI.AbstractCurveTrait =
zero(typeof(GI.x(GI.getpoint(curve, 1))))
# Points, MultiPoints, Curves, MultiCurves
_area(::Type{T}, ::GI.AbstractGeometryTrait, geom) where T = zero(T)

signed_area(trait::CT, curve) where CT <: GI.AbstractCurveTrait =
area(trait, curve)
_signed_area(::Type{T}, ::GI.AbstractGeometryTrait, geom) where T = zero(T)

# Polygons
area(trait::GI.PolygonTrait, geom) = abs(signed_area(trait, geom))
_area(::Type{T}, trait::GI.PolygonTrait, poly) where T =
abs(_signed_area(T, trait, poly))

function signed_area(::GI.PolygonTrait, poly)
s_area = _signed_area(GI.getexterior(poly))
function _signed_area(::Type{T}, ::GI.PolygonTrait, poly) where T
GI.isempty(poly) && return zero(T)
s_area = _signed_area(T, GI.getexterior(poly))
area = abs(s_area)
area == 0 && return area
# Remove hole areas from total
for hole in GI.gethole(poly)
area -= abs(_signed_area(hole))
area -= abs(_signed_area(T, hole))
end
# Winding of exterior ring determines sign
return area * sign(s_area)
end

# MultiPolygons
area(::GI.MultiPolygonTrait, geom) =
sum((area(poly) for poly in GI.getpolygon(geom)))
# # MultiPolygons and GeometryCollections
_area(
::Type{T},
::Union{GI.MultiPolygonTrait, GI.GeometryCollectionTrait},
geoms,
) where T =
sum((area(geom, T) for geom in GI.getgeom(geoms)), init = zero(T))

#=
Helper function:
Expand All @@ -108,20 +118,20 @@ to find the area under the curve. Even if curve isn't explicitly closed by
repeating the first point at the end of the coordinates, curve is still assumed
to be closed.
=#
function _signed_area(geom)
# Close curve, even if last point isn't explicitly repeated
function _signed_area(::Type{T}, geom) where T
area = zero(T)
# Close curve, even if last point isn't explicitly repeated
np = GI.npoint(geom)
np == 0 && return area
first_last_equal = equals(GI.getpoint(geom, 1), GI.getpoint(geom, np))
np -= first_last_equal ? 1 : 0
# Integrate the area under the curve
p1 = GI.getpoint(geom, np)
T = typeof(GI.x(p1))
area = zero(T)
for i in 1:np
p2 = GI.getpoint(geom, i)
# Accumulate the area into `area`
area += GI.x(p1) * GI.y(p2) - GI.y(p1) * GI.x(p2)
p1 = p2
end
return area / 2
return T(area / 2)
end
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