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Abstraction-bridges
Berend Schotanus First Flamingo Enterprise B.V.
Contents
- Background
- Reductionism - Holism
- Example: drawing curves in MapKit overlay
Abstraction-bridges Berend Schotanus First Flamingo Enterprise B.V. - - PowerPoint PPT Presentation
Abstraction-bridges Berend Schotanus First Flamingo Enterprise B.V. - - PowerPoint PPT Presentation
Abstraction-bridges Berend Schotanus First Flamingo Enterprise B.V. Contents Background Reductionism - Holism Example: drawing curves in MapKit overlay My Question: Snow, heat, autumn leaves... storm, bomb threat, signal passed
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My Question:
Snow, heat, autumn leaves... storm, bomb threat, signal passed at danger... How can the railway system go down like this, time after time?
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What makes this device different?
Not infallible... Yet it feels different, flexible, more natural, Less rigid.
illustratie: apple-history.com
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equation-based → simulation-based
reductionism → holism
analysis → computation
continuous → discrete
linear → non-linear
deterministic → stochastic abstract → detailed
- ne, two → many
homogeneous → composite
predictive → explanatory
realism → instrumentalism
centralized → decentralized
isolation → interaction
- n-to-many → many-to-many
top-down → bottom-up
analysis → computation
design → search
Aristotelian logic → many-valued logic
frequentist probability → Bayesianism
- bjective → subjective
physical law → theory → model
determinism → indeterminism
bron: A.B. Downey, Think Complexity
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Reductionism
illustratie: wikipedia/Alan Chia
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Holism
illustratie: cjouets.fr illustratie: brictechnic.fr
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Abstraction-bridges
Polyester LEGO-blocks Crane Construction-site Town low level of abstraction high level of abstraction
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Processor User low level of abstraction high level of abstraction
OS-X layered architecture
(from: Apple documentation)
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Lessons learned
- Railways tend to think in one level of
abstraction (timetable)
- Finding and connecting appropriate levels of
abstraction makes a system more flexible and resilient
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Hardware Traffic control Timetable Train-service Traveller
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Screen Scroll-view Map Infrastructure Train-service
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Drawing curves (1)
How to draw a curve
- n a map using the
MapKit overlay API
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Drawing curves (2)
void CGPathAddArc ( CGMutablePathRef path, const CGAffineTransform *m, CGFloat x, CGFloat y, CGFloat radius, CGFloat startAngle, CGFloat endAngle, bool clockwise ); = mapPointA = mapPointB (x, y) = mapPointC
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MapKit overlay
rendering engine subclass of MKOverlayView protocol MKOverlay your data
drawMapRect:zoomScale:inContext: ask data whatever
struct CGPoint { CGFloat x; CGFloat y; }; typedef struct CGPoint CGPoint; typedef struct { CLLocationDegrees latitude; CLLocationDegrees longitude; } CLLocationCoordinate2D; typedef struct { double x; double y; } MKMapPoint;
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Transformations
- (MKMapPoint)mapPointForPoint:(CGPoint)point
- (CGPoint)pointForMapPoint:(MKMapPoint)mapPoint
CGPoint MKMapPoint CLLocation Coordinate2D
MKMapPoint MKMapPointForCoordinate( CLLocationCoordinate2D coordinate ); CLLocationCoordinate2D MKCoordinateForMapPoint( MKMapPoint mapPoint );
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Custom transformations
angle
typedef struct {
- double angle;
- double length;
} PolarSize;
length width height
struct CGSize { CGFloat width; CGFloat height; }; typedef struct CGSize CGSize; CGSize cartesianSizeFromPolar(PolarSize polar) {
- CGSize result;
- result.width = polar.length * cos(polar.angle);
- result.height = polar.length * sin(polar.angle);
- return result;
} PolarSize polarSizeFromCartesian(CGSize size) {
- PolarSize result = polarSizeMake(0, pythagoras(size));
if (result.length > 0) { if (size.height > 0) { result.angle = acos(size.width/result.length); } else { result.angle = -acos(size.width/result.length); } }
- return result;
}
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[overlayView drawRect]
- (void)drawMapRect:(MKMapRect)mapRect zoomScale:(MKZoomScale)zoomScale inContext:(CGContextRef)context
{ RLARoute *route = (RLARoute*)self.overlay; CGMutablePathRef path = CGPathCreateMutable(); [route performOnAllMapPoints:^(MKMapPoint mapPointA, MKMapPoint mapPointB, MKMapPoint mapPointC){ CGPoint curveEnterPoint = [self pointForMapPoint:mapPointA]; CGPoint curveExitPoint = [self pointForMapPoint:mapPointB]; CGPoint curveCenterPoint = [self pointForMapPoint:mapPointC]; PolarSize curveEnterRadial = polarSizeFromCartesian(cartesianSizeFromLine(curveCenterPoint, curveEnterPoint)); PolarSize curveExitRadial = polarSizeFromCartesian(cartesianSizeFromLine(curveCenterPoint, curveExitPoint)); double deltaAngle = rangeMinusPiPlusPi(curveExitRadial.angle - curveEnterRadial.angle); CGPathAddArc(path, NULL, curveCenterPoint.x, curveCenterPoint.y, curveEnterRadial.length, curveEnterRadial.angle, curveExitRadial.angle, deltaAngle < 0); }]; CGContextAddPath(context, path); CGContextSetStrokeColorWithColor(context, [[UIColor blackColor] CGColor]); CGContextSetLineWidth(context, 1.0); CGContextStrokePath(context); CGPathRelease(path); }
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