Hacking Google Maps and Google Earth (ExtremeTech)

Chapter 13 — I Need to Get To... 265

message = document.getElementById(“message”);

rrecording = document.getElementById(“rrecording”);

routeidfield = document.getElementById(“routeid”);

routetitle = document.getElementById(“routetitle”);

routedescription = document.getElementById(“routedesc”);

routeidfield.value = 0;

routetitle.value = ‘’;

routedescription.value = ‘’;

map = new GMap(document.getElementById(“map”));

map.addControl(new GSmallZoomControl());

map.centerAndZoom(new GPoint(-0.64,52.909444), 2);

}

}

With the variables initialized, you create the mapobject, add a simple zoom control, and then

zoom to a suitable area on the map according to the application.

Recentering and Zooming the Map

The recenterandzoom()function is the same as that shown in previous chapters, starting

with Chapter 10. The function accepts an array of points, calculates the center point and span

of those points, and both centers and zooms the Google Map until all of the supplied points

are displayed on the map.

You can see that in this application the process works just as well on points used to generate

markers as it does to generate routes.

Backend Database Interface

The server side of the route recording system must respond to a number of requests from the

Google Maps application. There are four basic operations to be supported:

Listing existing routes


Saving a route

Deleting a route


Getting a route

Response is obviously through XML, but in addition to the standard responses for a given

operation, there is also a requirement to send back error messages in the event of some sort of

failure of the backend process.

In addition to the four main functions, a fifth function returns a standardized message (and,

optionally, a number of attributes) and is primarily used when a function needs to return an

error message. Using a single function in this way makes it easier for the format of the message

to be standardized regardless of the function generating the error.