LFHeatMap

iOS heat map package

Features

• extremely fast heat map generation from point/weight data pairs
• generates UIImage objects that can be overlaid as needed
• variable boost/bleed

Anti-Features

LFHeatMap is a simple UIImage generator. The resulting object can be used like any other UIImage, standalone or in a UIImageView. While it can be overlaid on top of a MKMapView, it is not strongly tied to this specific component and hence does not offer the benefits that come with a more complex implementation of MKOverlayRenderer.

Check out DTMHeatMap for an implementation supporting MKOverlay.

Adding LFHeatMap to Your Project

CocoaPods

CocoaPods is a dependency manager for Objective-C, which automates and simplifies the process of using 3rd-party libraries like LFHeatMap in your projects. See the “Getting Started” guide for more information.

platform :ios, '5.0'
pod "LFHeatMap"

Source Files

Alternatively you can directly add the LFHeatMap folder to your project.

.NET/Xamarin Port

https://github.com/rmarinho/LFHeatMap

Demo

This demo plots the measured magnitudes of the 2011 Virginia Earthquake.

Running

1. Open and launch the LFHeatMapDemo XCode project.
2. Move the slider on the bottom to adjust the boost.

Explanation

The data is stored in quake.plist which is a simple plist storing the latitude, longitude, and magnitude of each measurement. The points (locations) and weights (magnitudes) are stored in two NSArray objects in viewDidLoad of LFHeatMapDemoViewController.

The main action takes place in the sliderChanged: function. Moving the slider determines the new boost value and generates a new heat map image. The image’s dimensions are the same as the self.mapView object, with the points and weights supplied by the two data arrays. The image is then passed to the overlaying UIImageView that sits on top of the map.

LFHeatMap

This class contains the three basic static functions used to generate the heat maps.

1. Basic Heat Map

Supply the desired image dimensions and boost, as well as the point/value arrays. There should be a 1:1 mapping between these two arrays, that is each index in the points array should have a corresponding index in the weights array.

@params
rect: region frame
boost: heat boost value
points: array of NSValue CGPoint objects representing the data points
weights: array of NSNumber integer objects representing the weight of each point
 
@returns
UIImage object representing the heatmap for the specified region.
 
+ (UIImage *)heatMapWithRect:(CGRect)rect 
                       boost:(float)boost 
                      points:(NSArray *)points 
                     weights:(NSArray *)weights

2. Advanced Heat Map

Works generally the same as the basic heat map, but allows to tweak two additional parameters to control the “bleed” of heat rendering.

@params
rect: region frame
boost: heat boost value
points: array of NSValue CGPoint objects representing the data points
weights: array of NSNumber integer objects representing the weight of each point
weightsAdjustmentEnabled: set YES for weight balancing and normalization
groupingEnabled: set YES for tighter visual grouping of dense areas
 
@returns
UIImage object representing the heat map for the specified region.
 
+ (UIImage *)heatMapWithRect:(CGRect)rect 
                       boost:(float)boost 
                      points:(NSArray *)points 
                     weights:(NSArray *)weights 
    weightsAdjustmentEnabled:(BOOL)weightsAdjustmentEnabled
             groupingEnabled:(BOOL)groupingEnabled

3. MKMapView Helper

Works the same as the basic heat map, but allows you to supply map-specific parameters. Pass an MKMapView object (typically the target you want to overlay), and an array of CLLocation objects corresponding to coordinates on the specified MKMapView object.

The function will convert these to the required CGRect/CGPoint values as needed.

@params 
mapView: Map view representing the heat map area.
boost: heat boost value
locations: array of CLLocation objects representing the data points
weights: array of NSNumber integer objects representing the weight of each point
 
@returns
UIImage object representing the heatmap for the map region.

+ (UIImage *)heatMapForMapView:(MKMapView *)mapView
                         boost:(float)boost
                     locations:(NSArray *)locations
                       weights:(NSArray *)weights

License

LFHeatMap is available under the MIT license. See the LICENSE file for more info.

LF?

LFHeatMap comes from my work on the (now shut down) LocalFaves framework from Skyhook Wireless. This component has been open-sourced and formed the basis of a chapter in the Geolocation in iOS book.