Perimeter.fs

namespace OSBuildings

module Perimeter =

    // Need to include this Nuget package: https://www.nuget.org/packages/Huitian.EGIS.ShapeFileLib/
    // Need to add a reference to System.Drawing 

    let shpPath = @"C:\Data\OSBuildings\wales_buildings_clipped.shp"

    let demo1() =

        let sf = new EGIS.ShapeFileLib.ShapeFile(shpPath)
        
        Seq.init sf.RecordCount (sf.GetShapeData)
        |> Seq.take 10
        |> Seq.iter(fun c ->
            printfn "---"
            c
            |> Seq.iter (fun p ->
                printfn "%A" p))

    open System.Drawing

    let distance (p1: PointF, p2: PointF) =
        let dx = pown (p1.X - p2.X) 2
        let dy = pown (p1.Y - p2.Y) 2
        dx + dy |> sqrt

    let polyLength (ps : PointF seq) =
        ps
        |> Seq.pairwise
        |> Seq.sumBy distance
    
    // This will slightly overestimate the perimeter because it will
    // effectively join any 'voids' in the building with the main
    // perimeter.  How would you fix it?

    let maxPerimeter filePath =
        use sf = new EGIS.ShapeFileLib.ShapeFile(filePath)

        Seq.init sf.RecordCount (sf.GetShapeData)
        |> Seq.maxBy (fun pointGroups -> 
            pointGroups
            |> Seq.concat
            |> polyLength)

    maxPerimeter shpPath |> printfn "%A"
    
    open System.IO

    let maxPerimeterDir dirPath filePattern = 
        Directory.EnumerateFiles(dirPath, filePattern)
        |> Seq.collect (fun fileName ->
            let sf = new EGIS.ShapeFileLib.ShapeFile(fileName)
            Seq.init sf.RecordCount (sf.GetShapeData))
        |> Seq.maxBy (fun pointGroups -> 
            pointGroups
            |> Seq.concat
            |> polyLength)

    maxPerimeterDir @"C:\Data\OSBuildings" "*.shp" |> printfn "%A"