A shapefile reader in Swift

Description

Reads data from files in Shapefile format.

API Overview

ShapefileReader is the only object you instantiate.

Internally, it builds the three following objects, depending on the available auxiliary files:

• SHPReader to read the shapes, ie the list of points
• DBFReader to read the data records associated with the shapes
• SHXReader to read the indices of the shapes, thus allowing direct access

Most usages of ShapefileReader will remain like:

guard let sr = ShapefileReader(path: "g1g15.shp") else { assertionFailure() }

// iterate over both shapes and records
for (shape, record) in sr.shapeAndRecordGenerator() {
    // record is [AnyObject]

    for points in shape.partPointsGenerator() {
        // draw polygon with [CGPoint]
    }
}

DBF API

// if dbf file exists
if let dbf = sr.dbf {
    // number of records
    let n = dbf.numberOfRecords
    
    // fields description
    print(dbf.fields)
    
    // iterate over records
    for r in dbf.recordGenerator() {
        // ...
    }
    
    // access a record by index
    print(dbf[1847])
}

[[DeletionFlag, C, 1, 0], [GMDNR, N, 9, 0], [GMDNAME, C, 50, 0], [BZNR, N, 9, 0], [KTNR, N, 9, 0], [GRNR, N, 9, 0], [AREA_HA, N, 9, 0], [X_MIN, N, 9, 0], [X_MAX, N, 9, 0], [Y_MIN, N, 9, 0], [Y_MAX, N, 9, 0], [X_CNTR, N, 9, 0], [Y_CNTR, N, 9, 0], [Z_MIN, N, 9, 0], [Z_MAX, N, 9, 0], [Z_AVG, N, 9, 0], [Z_MED, N, 9, 0], [Z_CNTR, N, 9, 0]]  
[5586, Lausanne, 2225, 22, 1, 4138, 534438, 544978, 150655, 161554, 538200, 152400, 371, 930, 670, 666, 585]

SHX API

// if index file exists
if let shx = sr.shx {
    // access a shape by index
    if let offset = shx.shapeOffsetAtIndex(2) {
    	if let (nextIndex, shape) = shp.shapeAtOffset(offset) {
	        // use shape   	
    	}
    }
}

or more simply

let shape = sr[2]

Implementation Details

• shape points are CGPoint arrays
• record are arrays of Int, Double, Bool or String (no NSDate, no optionals)
• random access in files and enumerators are used each time it is possible
• most of time, code will crash when files do not match the specs, feel free to open an issue an join the offending files

Tests and Drawing

The project comes with a unit test target.

Also, it comes with BitmapCanvas and its subclass BitmapCanvasShapefile which will generate the following PNG file.

You just need to change the path at the beginning of the draw() function in main.swift according the project's location.

TODO

Handle projection files, eg. from http://www.gadm.org/download.