public
Created

A category on MKPolyline adding a class method to create a new MKPolyline from a Google Maps Directions API encoded polyline string. See https://developers.google.com/maps/documentation/utilities/polylinealgorithm

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MKPolyline+GMEncodedString.h
Objective-C
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#import <MapKit/MapKit.h>
 
@interface MKPolyline (GMEncodedString)
 
+ (MKPolyline *)polylineWithGMEncodedString:(NSString *)encodedString;
 
@end
MKPolyline+GMEncodedString.m
Objective-C
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#import "MKPolyline+GMEncodedString.h"
 
@implementation MKPolyline (GMEncodedString)
 
+ (MKPolyline *)polylineWithGMEncodedString:(NSString *)encodedString {
const char *bytes = [encodedString UTF8String];
NSUInteger length = [encodedString lengthOfBytesUsingEncoding:NSUTF8StringEncoding];
NSUInteger idx = 0;
NSUInteger count = length / 4;
CLLocationCoordinate2D *coords = calloc(count, sizeof(CLLocationCoordinate2D));
NSUInteger coordIdx = 0;
float latitude = 0;
float longitude = 0;
while (idx < length) {
char byte = 0;
int res = 0;
char shift = 0;
do {
byte = bytes[idx++] - 63;
res |= (byte & 0x1F) << shift;
shift += 5;
} while (byte >= 0x20);
float deltaLat = ((res & 1) ? ~(res >> 1) : (res >> 1));
latitude += deltaLat;
shift = 0;
res = 0;
do {
byte = bytes[idx++] - 0x3F;
res |= (byte & 0x1F) << shift;
shift += 5;
} while (byte >= 0x20);
float deltaLon = ((res & 1) ? ~(res >> 1) : (res >> 1));
longitude += deltaLon;
float finalLat = latitude * 1E-5;
float finalLon = longitude * 1E-5;
CLLocationCoordinate2D coord = CLLocationCoordinate2DMake(finalLat, finalLon);
coords[coordIdx++] = coord;
if (coordIdx == count) {
NSUInteger newCount = count + 10;
coords = realloc(coords, newCount * sizeof(CLLocationCoordinate2D));
count = newCount;
}
}
MKPolyline *polyline = [MKPolyline polylineWithCoordinates:coords count:coordIdx];
free(coords);
return polyline;
}
 
@end

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