Initial Commit

.github/workflows/ci.yml

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+# This workflow will build a golang project
+# For more information see: https://docs.github.com/en/actions/automating-builds-and-tests/building-and-testing-go
+
+name: CI
+
+on:
+  push:
+    branches: ["master"]
+
+  pull_request:
+    branches: ["master"]
+
+permissions: {}
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@692973e3d937129bcbf40652eb9f2f61becf3332 # v4.1.7
+
+      - name: Set up Go
+        uses: actions/setup-go@0a12ed9d6a96ab950c8f026ed9f722fe0da7ef32 # v5.0.2
+        with:
+          go-version: "stable"
+
+      - name: Test
+        run: go test -v -cover -coverprofile=coverage.coverprofile ./...
+
+      - name: Upload coverage reports to Codecov
+        uses: codecov/codecov-action@e28ff129e5465c2c0dcc6f003fc735cb6ae0c673 # v4.5.0
+        env:
+          CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}

LICENCE

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+The MIT License (MIT)
+
+Copyright (c) 2024 Hikmatulloh Hari Mukti
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

README.md

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+# Carto
+
+![GitHub Workflow Status](https://github.com/muktihari/carto/workflows/CI/badge.svg)
+[![Go Reference](https://pkg.go.dev/badge/github.com/muktihari/carto.svg)](https://pkg.go.dev/github.com/muktihari/carto)
+[![CodeCov](https://codecov.io/gh/muktihari/carto/branch/master/graph/badge.svg)](https://codecov.io/gh/muktihari/carto)
+[![Go Report Card](https://goreportcard.com/badge/github.com/muktihari/carto)](https://goreportcard.com/report/github.com/muktihari/carto)
+
+This project hosts the implementation of various Cartography algorithms in Go.
+
+## Import
+
+```sh
+go get github.com/muktihari/carto
+```
+
+## List of algorithms:
+
+- [Ramer–Douglas–Peucker](https://w.wiki/B6U3) [[github.com/muktihari/carto/rdp](./rdp/rdp.go)]: Simplifies a curve by reducing the number of points in a curve composed of line segments, resulting in a similar curve with fewer points. It's a zero-alloc implementation that performs efficiently by reslicing the input **points**.
+
+  ![rdp](./docs/rdp_sample.svg)
+
+  Benchmark (n = 1000 points):
+
+  ```js
+  goos: linux; goarch: amd64; pkg: github.com/muktihari/carto/rdp
+  cpu: Intel(R) Core(TM) i5-5257U CPU @ 2.70GHz
+  BenchmarkSimplify-4   6428   161746 ns/op   0 B/op   0 allocs/op
+  PASS
+  ok      github.com/muktihari/carto/rdp  1.065s
+  ```

go.mod

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+module github.com/muktihari/carto
+
+go 1.20.0
+
+require github.com/google/go-cmp v0.6.0

go.sum

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+github.com/google/go-cmp v0.6.0 h1:ofyhxvXcZhMsU5ulbFiLKl/XBFqE1GSq7atu8tAmTRI=
+github.com/google/go-cmp v0.6.0/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=

rdp/rdp.go

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+// Package rdp host the implementation of [Ramer–Douglas–Peucker algorithm](https://w.wiki/B6U3) algorithm.
+package rdp
+
+import "math"
+
+// Point represents coordinates in 2D plane.
+type Point struct {
+	X, Y  float64 // X and Y represent coordinates (e.g Latitude and Longitude)
+	Index int     // [Optional] Index reference to the origin data.
+}
+
+// Simplify simplifies a curve by reducing the number of points in a curve composed of line segments,
+// resulting in a similar curve with fewer points. Ref: [Ramer–Douglas–Peucker algorithm](https://w.wiki/B6U3).
+//
+// Note: The resulting slice is a reslice of given points (it shares the same underlying array) for efficiency.
+// It works similar to append, so the input points should not be used after this call, use only the returned value.
+func Simplify(points []Point, epsilon float64) []Point {
+	if len(points) < 2 {
+		return points
+	}
+
+	var (
+		index   int
+		maxDist float64
+		first   = points[0]
+		last    = points[len(points)-1]
+	)
+
+	for i := range points {
+		d := perpendicularDistance(points[i], first, last)
+		if d > maxDist {
+			maxDist = d
+			index = i
+		}
+	}
+
+	if maxDist <= epsilon {
+		return append(points[:0], first, last)
+	}
+
+	firstHalf, lastHalf := points[:index], points[index:]
+
+	return append(Simplify(firstHalf, epsilon), Simplify(lastHalf, epsilon)...)
+}
+
+// perpendicularDistance calculates the perpendicular distance from a point to a line segment
+func perpendicularDistance(p, start, end Point) float64 {
+	if start.X == end.X && start.Y == end.Y {
+		return euclidean(start, end)
+	}
+	numerator := math.Abs((end.Y-start.Y)*p.X - (end.X-start.X)*p.Y + end.X*start.Y - end.Y*start.X)
+	denominator := euclidean(start, end)
+	return numerator / denominator
+}
+
+// euclidean calculates the distance between two points.
+func euclidean(p1, p2 Point) float64 {
+	x := p2.X - p1.X
+	y := p2.Y - p1.Y
+	return math.Sqrt(x*x + y*y)
+}