topic Re: intersection in ArcGIS Runtime SDK for iOS Questions

intersection

BrettDavidson — Wed, 04 Jan 2017 16:42:25 GMT

The Question: Can ArcGIS SDK for iOS in Objective C find this solution with precision utilizing Lat/Long coordinates for ABCD to find E? if so! HOW?

Re: intersection

BrettDavidson — Wed, 04 Jan 2017 17:04:09 GMT

How do you input for the coordinates for lineAB? This would be two sets of coordinates. I have not dealt with ArcGIS SDK for iOS yet. Can you explain for me?

Re: intersection

RyanOlson1 — Sat, 11 Dec 2021 23:15:49 GMT

Actually - you should get back a line when intersecting 2 lines. My first answer above is incorrect, I will remove it for clarity.

Code should look something like this:

-(void)lineIntersection{
    AGSPolyline *lineAB = [AGSPolyline polylineWithPoints:@[AGSPointMakeWGS84(0, 0), AGSPointMakeWGS84(10, 10)]];
    AGSPolyline *lineCD = [AGSPolyline polylineWithPoints:@[AGSPointMakeWGS84(0, 10), AGSPointMakeWGS84(10, 0), AGSPointMakeWGS84(5, 10), AGSPointMakeWGS84(0, 0), AGSPointMakeWGS84(10, 10)]];
    AGSPolyline *lineE = (AGSPolyline*)[AGSGeometryEngine intersectionOfGeometry1:lineAB geometry2:lineCD];
    NSLog(@"lineE: %@", lineE);
}‍‍‍‍‍‍

Re: intersection

BrettDavidson — Wed, 04 Jan 2017 20:22:54 GMT

Hello,

I got NSLog reply of:
lineE: AGSPolyline: [], sr: 4326

How do I get the lat/long from lineE?

Re: intersection

MichaelDavis3 — Wed, 04 Jan 2017 20:49:51 GMT

Wouldn't the AGSGeometry returned by the Geometry Engine be a point, not a polyline?

Re: intersection

RyanOlson1 — Sat, 11 Dec 2021 23:15:52 GMT

Brett,

Nick Furness pointed out to me that you need to actually union the lines together first to get what you are looking for.

Here is objective-c code to do what you need:

@interface AGSPolyline (intersects)

-(NSArray<AGSPoint*>*)intersectionWithLine:(AGSPolyline*)line2;

@end


@implementation AGSPolyline (intersects)

-(NSArray<AGSPoint*>*)intersectionWithLine:(AGSPolyline*)line2{
    
    
    NSMutableArray *points = [NSMutableArray array];
    
    // first union the lines together
    AGSPolyline *lineUnion = (AGSPolyline*)[AGSGeometryEngine unionOfGeometry1:self geometry2:line2];
    
    // now get the intersecting line of union'ed line and self
    AGSPolyline *line3 = (AGSPolyline*)[AGSGeometryEngine intersectionOfGeometry1:self geometry2:lineUnion];
    
    double tolerance = 1e-10;
    
    for (AGSPart *part in line3.parts){
        for (AGSPoint *point in part.points){
            double distance = [AGSGeometryEngine distanceBetweenGeometry1:point geometry2:line2];
            
            // if the point is on the passed-in line then add it to the return value
            if (distance < tolerance){
                [points addObject:point];
            }
        }
    }
    
    return [points copy];
}

@end


-(void)testLineIntersection{
    AGSPolyline *lineAB = [AGSPolyline polylineWithPoints:@[AGSPointMakeWGS84(0, 0), AGSPointMakeWGS84(10, 10)]];
    AGSPolyline *lineCD = [AGSPolyline polylineWithPoints:@[AGSPointMakeWGS84(0, 10), AGSPointMakeWGS84(10, 0)]];
    
    NSArray *pointsE = [lineAB intersectionWithLine:lineCD];
    
    NSLog(@"intersection points: %@", pointsE);
}
‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

Thanks to Nick Furness for pointing this out. He also provided the swift code, which I converted to objective-c.

Re: intersection

Nicholas-Furness — Thu, 05 Jan 2017 17:51:11 GMT

Thanks for posting that, Ryan Olson‌.

For reference, here's a Gist with the Swift code: Runtime Line Intersection Points · GitHub

The Gist also discusses a potential edge-case worth being aware of, depending on how your input data is generated.

Re: intersection

BrettDavidson — Sat, 07 Jan 2017 01:41:50 GMT

Thank you sir I will try as soon as I get time. I currently have 42 warnings from the install of the SDK, trying to work them out..

Re: intersection

BrettDavidson — Sat, 07 Jan 2017 01:52:45 GMT

Input data is generated, by manual input on:

CGPoint   p1 = CGPointMake(32.734444, -116.577499);CGPoint   p2 = CGPointMake(32.7337, -117.008);CGPoint   p3 = CGPointMake(33.363609, -116.836388);CGPoint   p4 = CGPointMake(32.64, -116.836);

-(void)lineIntersection{

AGSPolyline *lineAB = [AGSPolyline polylineWithPoints:@[AGSPointMakeWGS84(p1), AGSPointMakeWGS84(p2)]];

AGSPolyline *lineCD = [AGSPolyline polylineWithPoints:@[AGSPointMakeWGS84(p3), AGSPointMakeWGS84(p4)]];

NSArray *pointsE = [lineAB intersectionWithLine:lineCD];

NSLog(@"intersection points: %@", pointsE);

}