130 lines
3.2 KiB
Ruby
130 lines
3.2 KiB
Ruby
class GeojsonService
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def self.to_json_polygon_for_cadastre(coordinates)
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polygon = {
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geom: {
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type: "Feature",
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geometry: {
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type: "Polygon",
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coordinates: [
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coordinates
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]
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}
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}
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}
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polygon.to_json
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end
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# The following code is ported from turfjs
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# https://github.com/Turfjs/turf/blob/master/packages/turf-area/index.ts
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EQUATORIAL_RADIUS = 6378137
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def self.area(geojson)
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calculate_area(geojson)
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end
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def self.length(geojson)
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segment_reduce(geojson, 0) do |previous_value, segment|
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coordinates = segment[:geometry][:coordinates]
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previous_value + distance(coordinates[0], coordinates[1])
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end
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end
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def self.distance(from, to)
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coordinates1 = from
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coordinates2 = to
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d_lat = degrees_to_radians(coordinates2[1] - coordinates1[1])
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d_lon = degrees_to_radians(coordinates2[0] - coordinates1[0])
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lat1 = degrees_to_radians(coordinates1[1])
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lat2 = degrees_to_radians(coordinates2[1])
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a = (Math.sin(d_lat / 2)**2) + (Math.sin(d_lon / 2)**2) * Math.cos(lat1) * Math.cos(lat2)
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radians = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a))
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radians * EQUATORIAL_RADIUS
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end
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def self.calculate_area(geom)
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total = 0
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case geom[:type]
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when 'Polygon'
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polygon_area(geom[:coordinates]);
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when 'MultiPolygon'
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geom[:coordinates].each do |coordinates|
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total += polygon_area(coordinates)
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end
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total
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else
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total
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end
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end
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def self.polygon_area(coordinates)
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total = 0
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if coordinates.present?
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coordinates = coordinates.dup
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total += ring_area(coordinates.shift).abs
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coordinates.each do |coordinates|
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total -= ring_area(coordinates).abs
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end
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end
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total
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end
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def self.ring_area(coordinates)
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total = 0
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coords_length = coordinates.size
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if coords_length > 2
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coords_length.times do |i|
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if i == coords_length - 2 # i = N-2
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lower_index = coords_length - 2
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middle_index = coords_length - 1
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upper_index = 0
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elsif i == coords_length - 1 # i = N-1
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lower_index = coords_length - 1
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middle_index = 0
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upper_index = 1
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else # i = 0 to N-3
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lower_index = i
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middle_index = i + 1
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upper_index = i + 2
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end
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p1 = coordinates[lower_index]
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p2 = coordinates[middle_index]
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p3 = coordinates[upper_index]
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total += (rad(p3[0]) - rad(p1[0])) * Math.sin(rad(p2[1]))
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end
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total = total * EQUATORIAL_RADIUS * EQUATORIAL_RADIUS / 2
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end
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total
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end
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def self.segment_reduce(geojson, initial_value)
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previous_value = initial_value
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started = false
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coordinates = geojson[:coordinates].dup
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from = coordinates.shift
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coordinates.each do |to|
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current_segment = { type: 'Feature', geometry: { type: 'LineString', coordinates: [from, to] } }
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from = to
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if started == false && initial_value.blank?
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previous_value = current_segment
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else
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previous_value = yield previous_value, current_segment
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end
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started = true
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end
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previous_value
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end
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def self.rad(num)
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num * Math::PI / 180
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end
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def self.degrees_to_radians(degrees)
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rad(degrees % 360)
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end
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end
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