Gdal type provider

This is a starting point in developing a type provider for geospatial data files managed with the gdal library

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open FSharp.Gdal

open OSGeo
open OSGeo.GDAL
open OSGeo.OGR

open Deedle
open FSharp.Data
open FSharp.Charting

The shape file itinerari.shp contains the foot paths to the main peaks in the Val Grande National Park.

To get the data from a file we can just call the type provider constructor giving the file path as the type parameter of the provider. Internally the provider calls the logic needed to configure the gdal library on the system and to initialize all the gdal data providers:

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let vLayer = new OgrTypeProvider<"G:/Data/itinerari.shp">()

The type provider provides two properties:

Values which we can convert directly to a deedle frame to explore immediately the data in the vector:

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let fmData = vLayer.Values |> Frame.ofValues

and Features which we can iterate to get, for each feature, attributes and geometry converted in dinamically created types that match the type of geometry and attributes and come up directly with the intellisense in the iteractive editor:

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for feat in vLayer.Features do
    printfn "Geomtry type = %A\tID = %i\tTITLE = %s\t" 
        (feat.Geometry.GetGeometryType()) feat.ID feat.TITLE

Geomtry type = wkbLineString	ID = 1	TITLE = Cima Sasso	
Geomtry type = wkbLineString	ID = 4	TITLE = Pizzo Proman	
Geomtry type = wkbLineString	ID = 2	TITLE = Monte Faie	
Geomtry type = wkbLineString	ID = 3	TITLE = Cima Corte Lorenzo	
Geomtry type = wkbLineString	ID = 5	TITLE = Cima Saler	
Geomtry type = wkbLineString	ID = 6	TITLE = Pizzo delle Pecore	
Geomtry type = wkbLineString	ID = 12	TITLE = Cima Pedum	
Geomtry type = wkbLineString	ID = 7	TITLE = Punta Pozzolo	
Geomtry type = wkbLineString	ID = 8	TITLE = Pizzo Tignolino	
Geomtry type = wkbLineString	ID = 9	TITLE = Monte Togano	
Geomtry type = wkbLineString	ID = 10	TITLE = Pizzo Nona	
Geomtry type = wkbLineString	ID = 11	TITLE = Cima della Laurasca	
Geomtry type = wkbLineString	ID = 13	TITLE = Cimone di Cortechiuso	
Geomtry type = wkbLineString	ID = 14	TITLE = Monte Torrione	
Geomtry type = wkbLineString	ID = 15	TITLE = La Piota	
Geomtry type = wkbLineString	ID = 16	TITLE = Monte Zeda da Falmenta	
Geomtry type = wkbLineString	ID = 17	TITLE = Pizzo Marona dall'Alpe Pala	
Geomtry type = wkbLineString	ID = 17	TITLE = Pizzo Marona da Cicogna

We can also graphically visualize the features geometries using the plot function which is described in the Plot Geometries appendix:

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let footPaths = new OGR.Geometry(OGR.wkbGeometryType.wkbMultiLineString)

for feat in vLayer.Features do
    let _ = footPaths.AddGeometry(feat.Geometry)
    ()

footPaths |> plot

With the deedle frame and gdal methods at hand we can do some calculations based on geometries. The data file contains hiking paths in the Big Valley and we can for example get the lenght of each with the gdal library methods and use the deedle functions to aggregate them.

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let fmLengths = 
    vLayer.Features
    |> Seq.mapi (fun i feat -> i, "Length", feat.Geometry.Length())
    |> Frame.ofValues

let fmWithLengths = fmData.Join(fmLengths)

And just to do an aggregation:

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let sumLenghts = fmWithLengths.Sum()?Length

printf "sumLenghts = %f" sumLenghts

sumLenghts = 138959.383896

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