在Java中向展开的地图添加标记

Question

I need to add code to display a marker at the location of each earthquake in the RSS feed and make the radius of each marker 10 by modifying the methods (and adding new helper methods as necessary). Then I need to add code to style each marker according to the magnitude of its earthquake.

I know that I should create a SimplePointMarker object for each PointFeature in the list features, inside the setUp method for making markers appear on the screen, so it'll probably involve for each loops, but other then that I'm not sure how to code this.

Unfolding marker package explanation... http://unfoldingmaps.org/javadoc/

public class EarthquakeCityMap extends PApplet {

    // You can ignore this.  It's to keep eclipse from generating a warning.
    private static final long serialVersionUID = 1L;

    // IF YOU ARE WORKING OFFLINE, change the value of this variable to true
    private static final boolean offline = false;

    // Less than this threshold is a light earthquake
    public static final float THRESHOLD_MODERATE = 5;
    // Less than this threshold is a minor earthquake
    public static final float THRESHOLD_LIGHT = 4;

    /** This is where to find the local tiles, for working without an Internet connection */
    public static String mbTilesString = "blankLight-1-3.mbtiles";

    // The map
    private UnfoldingMap map;

    //feed with magnitude 2.5+ Earthquakes
    private String earthquakesURL = "http://earthquake.usgs.gov/earthquakes/feed/v1.0/summary/2.5_week.atom";


    public void setup() {
        size(950, 600, OPENGL);

        if (offline) {
            map = new UnfoldingMap(this, 200, 50, 700, 500, new MBTilesMapProvider(mbTilesString));
            earthquakesURL = "2.5_week.atom";   // Same feed, saved Aug 7, 2015, for working offline
        }
        else {
            map = new UnfoldingMap(this, 200, 50, 700, 500, new Google.GoogleMapProvider());
            // IF YOU WANT TO TEST WITH A LOCAL FILE, uncomment the next line
            //earthquakesURL = "2.5_week.atom";
        }

        map.zoomToLevel(2);
        MapUtils.createDefaultEventDispatcher(this, map);   

        // The List you will populate with new SimplePointMarkers
        List<Marker> markers = new ArrayList<Marker>();

        //Use provided parser to collect properties for each earthquake
        //PointFeatures have a getLocation method
        List<PointFeature> earthquakes = ParseFeed.parseEarthquake(this, earthquakesURL);

        // These print statements show you (1) all of the relevant properties 
        // in the features, and (2) how to get one property and use it
        if (earthquakes.size() > 0) {
            PointFeature f = earthquakes.get(0);
            System.out.println(f.getProperties());
            Object magObj = f.getProperty("magnitude");
            float mag = Float.parseFloat(magObj.toString());
            // PointFeatures also have a getLocation method
        }

        // Here is an example of how to use Processing's color method to generate 
        // an int that represents the color yellow.  
        int yellow = color(255, 255, 0);
        int red = color(255, 0, 0);
        int blue = color(0, 0, 255); 
        //TODO: Add code here as appropriate
    }

    // A suggested helper method that takes in an earthquake feature and     
    // returns a SimplePointMarker for that earthquake
    // TODO: Implement this method and call it from setUp, if it helps
    private SimplePointMarker createMarker(PointFeature feature)
    {
        //feature.setColor(color(150, 150, 150)); 

        // finish implementing and use this method, if it helps.
        return new SimplePointMarker(feature.getLocation());

        //earthquakeMarkers = MapUtils.create
    }

    public void draw() {
        background(10);
        map.draw();
        addKey();
    }

    // helper method to draw key in GUI
    // TODO: Implement this method to draw the key
    private void addKey() 
    {
        // Remember you can use Processing's graphics methods here
        fill(255, 250, 240); //color white
        rect(25, 50, 150, 250); // (x location of upper left corner, y location of upper left corner, width, height)

        fill(0); //needed for text to appear, sets the color to fill shapes, takes in an int rgb value
        textAlign(LEFT, CENTER);
        textSize(12);
        text("Earthquake Key", 50, 75); //heading of key, takes (string, float x, and float y)

        fill(color(255, 0, 0)); //red
        ellipse(50, 125, 15, 15); //(x coordinate, y coordinate, width, height)   )
        fill(color(255, 255, 0)); //yellow 
        ellipse(50, 175, 10, 10);
        fill(color(0, 0, 255));
        ellipse(50, 225, 5, 5);

        fill(0, 0, 0);
        text("5.0+ Magnitude", 75, 125);
        text("4.0+ Magnitude", 75, 175); // same y coordinate but different x so it could appear right beside marker
        text("Below 4.0", 75, 225);
    }
}

Answer 1

It's very glad to meet a person who enrolled the same course in COURSERA.

First, this part is just a example to show you how to extract "magnitude" as a float.

// These print statements show you (1) all of the relevant properties 
// in the features, and (2) how to get one property and use it

if (earthquakes.size() > 0) {
    PointFeature f = earthquakes.get(0);
    System.out.println(f.getProperties());
    Object magObj = f.getProperty("magnitude");
    float mag = Float.parseFloat(magObj.toString());
// PointFeatures also have a getLocation method
}

Let's check types of object and flow of thought in this example. It's very important to understand this part to complete assignment. The line "earthquakes.get()" means to get only the first object from the earthquakes, list of objects.

• earthquake: List of PointFeature Objects
• f: just ONE PointFeature object from earthquakes
• magObj: "magnitude" value as a object from f
• mag: final float value of magnitude

In this problem, you don't need to define a new variable. My pseudocode is like this.

1. Use for~ loop
   for (PointFeature f : earthquakes) {  ...  }

2. Create new instance of SimplePointMarker 
   Check API document of SimplePointMarker class.
   It needs a Location as a parameter and returns SimplePointMarker object.
   You can get the location parameter easily, 
   because SimplePointMarker implements Maker interface.
   Just use 'getLocation()' method. 
   You made a many markers (SimplePointMaker)!

   After making many makers, you can practice with some methods.
   Ex) marker.setColor(yellow), marker.setRadius(10) 

3. What you have to do is only to add makers to map.
   Check API document again. (Map class)
   Map class has addMarker(Marker marker) method.
   You can use it out of for loop.

4. Your addKey() method is Great!

I hope this will help you.

Answer 2

 //add this in setup method    
 for(PointFeature ia: earthquakes) {
         SimplePointMarker to = createMarker(ia);//using given healper method
         to.setRadius(10.0f); 

         Object magObj = ia.getProperty("magnitude");
         float mag = Float.parseFloat(magObj.toString());
         if(mag >= 5.0f ){

              to.setColor(red);
              }
         else if(mag >= 4.0f ){

              to.setColor(yellow);
              }
         else{

              to.setColor(blue);
              }

          markers.add(to);//adding created simplepointmarkers to(to) arraylist


     }//end of for loop

   map.addMarkers(markers)//entire list of markers is  added to map
}//end of setup()

Answer 3

You should be able to put the default markers (grey) before you start to customize them.

Your createMarker method gets a specific earthquake and returns a default marker with location. So, you should be able to pass the earthquakes into this method one by one to have markers for every earthquake. (That does not mean you will change the createMarker method. Passing will be done by a for loop inside the setup method.)

A thing we will do for a specific earthquake will be done for every earthquake, so we will work in the for loop from now on. Once you created a default marker, you should draw it on the map with another method. (You can check on how to draw the markers onto the map via the LifeExpectancy.java example.)

The coloring and sizing of the markers won't be challenging when you manage to draw the default ones.

Answer 4

I have a complete code for this:

List<PointFeature> earthquakes = ParseFeed.parseEarthquake(this,earthquakesURL);

for(PointFeature ft : earthquakes){
    markers.add(new SimplePointMarker(ft.getLocation(), ft.getProperties()));
}

map.addMarkers(markers);

for(Marker mk1 : markers){
    if((float) mk1.getProperty("magnitude") > 5.0)
        mk1.setColor(red);
    else{
        if((float) mk1.getProperty("magnitude") > 4.0 && 
           (float) mk1.getProperty("magnitude") < 5.0)
            mk1.setColor(yellow);
        else
            mk1.setColor(blue);
        }
    }
    map.addMarkers(markers);
}