R x at 09:11, 15 December 2010

2010-12-15T09:11:53Z

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This is a short manual describing how to retrieve the map tile image urls using the Fiddler.

= Introduction =
[http://www.fiddler2.com/fiddler2/version.asp Fiddler] is a local HTTP proxy written in DotNet - therefore in runs only under Windows. Install the latest 2.0 (beta) version; this is the version I recommend.

Together with Fiddler a FireFox plugin is installed that allows to easily enable/disable redirection of web traffic through Fiddler.

= Starting up =

Start Fiddler and Firefox. If everything is correct you should see the in the status bar that the Fiddler-plugin is working and if it is '''ON''' all traffic is redirected through Fiddler.

[[File:Firefox-Fiddler.png]]

For this manual we show how to develop the Yahoo map source. Therefore open [[http://maps.yahoo.com]] in Firefox and switch to Fiddler. You should see now a long list of HTML-, JavaScript- and image-files and their URL that has been loaded via HTTP.

[[File:Fiddler1.png|frameless|border|500px|link=http://sourceforge.net/apps/mediawiki/mobac/nfs/project/m/mo/mobac/8/8c/Fiddler1.png]]

= Finding the map tile images =

Most of the loaded files are of absolutely no interest for us. Only some of the images are what we are searching. By enabling the '''Image View''' on the '''Inspectors''' tab you can click through the images until you have found what looks like a map image tile.

[[File:Fiddler2.png|frameless|border|500px|link=http://sourceforge.net/apps/mediawiki/mobac/nfs/project/m/mo/mobac/e/e8/Fiddler2.png]]

If you don't find any map tile images go back to Firefox and move the map a bit around or switch to a different zoom level. You can force loading of the tiles you you look a a region you have never visited before because otherwise Firefox may have cached the tiles already and therefore does not load them which means that they do not appear in Fiddler.

= Detecting the URL pattern =

Now we come to a more complicated part - detecting the URL pattern. For that purpose you should collect several URLs of map tile images (you can copy the URL of the selected entry by pressing ''Ctrl + U'').
Save them for example in a new text file - then go back to Fiddler and clear the list ('''Remove''' -> '''All''). Go back to Firefox and change the zoom level; switch back to Fiddler and copy the relevant URLs to your text file.

If you do that several times you will get a large list of URLs looking similar to this one:

http://maps2.yimg.com/hx/tl?b=1&v=4.3&.intl=en&x=2&y=0&z=4&r=1
http://maps1.yimg.com/hx/tl?b=1&v=4.3&.intl=en&x=0&y=-1&z=4&r=1
http://maps1.yimg.com/hx/tl?b=1&v=4.3&.intl=en&x=4&y=1&z=5&r=1
http://maps2.yimg.com/hx/tl?b=1&v=4.3&.intl=en&x=4&y=2&z=5&r=1

You may notice that the base URL (before the question mark of only differ in the used server (''maps1.yimg.com'' and ''maps2.yimg.com''). Usually you can ignore this difference as this is only for load-balancing the traffic between two available servers. The interesting part is the part after the question mark. There are also some static parts that do not change ('''b=1&v=4.3''', '''&r=1'''), some that change with each map tile ('''&x=..''', '''&y=..''') and some that only change when the zoom level has been changed ('''&z=..''').

Now we have a basic understanding how a tile image URL does look like and what their parameter are for.

Fiddler - Revision history

R x at 09:11, 15 December 2010