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What is KML?

KML is type of markup language based off of XML.

Stands for Keyhole Markup Language

Developed by Keyhole Inc. Google

KML files are very often distributed in KMZ files, which are zipped KML files with a .kmz extension

Origin of KML

KML was first known as Keyhole.

KML originally developed for use with Google Earth.

Its development was engineered by Keyhole, Inc which Google acquired in 2004.

Definition

Keyhole Markup Language (KML) is an XML notation for expressing geographic annotation and visualization within Internet-based, two-dimensional maps and three-dimensional Earth browsers

In Other Words

KML is a way of displaying geographical data in an Earth Browser such as,

KML Functions

KML includes features that allow it to display:

place marks

Images

Polygons

3D models

Textual descriptions

Example

<?xml version="1.0" encoding="UTF-8"?>

<kml xmlns="http://earth.google.com/kml/2.0">

<Placemark>

<description>New York City</description>

<name>New York City</name>

<Point>

<coordinates>-74.006393,40.714172,0</coordinates>

</Point>

</Placemark>

</kml>

This is the previous script:

KML Applications:

KML file types are used by programs such as: ArcGIS Explorer Flickr Google Earth Google Maps Google Mobile Live Search Maps Microsoft Virtual Earth Marble (KDE) World Wind Yahoo Pipes

Google Maps and KML

KML Elements

Everything is an “Object”. (Everything inherits from the abstract “Object” KML element).

There are abstract elements Everything is a tag:

<Point>…</Point> The more advanced tags are (usually) for

Google Earth.

Google Maps supports a subset of KML…

Google Maps supports… Placemarks Icons Folders Descriptive HTML KMZ (compressed KML, including attached images) Polylines and polygons Styles for polylines and polygons, including color, fill, and opacity Network links to import data dynamically Ground overlays and screen overlays

Structure

KML is in XML format Usually everything contained in

Document tag Can have multiple Folder tags to

separate different kinds of data. For example, one folder containing KML to show locations of pictures and another folder containing KML to show your path through the day.

Placemarks/Points/Coordinates

The easiest element in KML. A simple point on the map. It only needs a name and a location. You can

give it a description too. Placemark tag defines the place mark A Point tag within it defines where the Placemark will be. A “type” called coordinate defines the Point. Coordinates in KML are given long,lat. When typing in coordinates

directly into Google Maps, they are given lat,long. Be careful!

Contd.

Descriptive HTML

You’ll probably want to do HTML within the description tag. You need to use the CDATA tag for this. If you don’t, your HTML’s tags

need to use entity references:

Paths

Can define a path using the Placemark tag and the LineString tag instead of the Point tag.

Multiple coordinates. Again by long,lat,alt. “extrude” tag makes the line go down to the ground “tessellate” breaks each line into multiple pieces.

Good for long lines so they don’t end up underground.

0 = false, 1 = true

Contd.

Advanced KML

Advanced KML

MIME Types

Styles

Screen Overlays

Network Links

MIME Type

KML Servers must follow certain rules

Must return response code of HTTP 200

The type itself is:application/vnd.google-earth.kml+xml

Can set the type in PHP with: header('Content-type: application/vnd.google-earth.kml+xml');

Body must contain valid KML data and the XML declaration:<?xml version="1.0" encoding="UTF-8"?>

Styles

Similar to CSS/HTML styles. In a Style tag. Each style tag can have multiple styles within it:

LineStyle, PolyStyle, ColorStyle, etc. The tag has an “id” so it can be referenced within a file or from another.

(A Global KML Style file perhaps?) Add a styleUrl element to use a style. HW2 could have different icons based on content? A site that grabs all

the Google Map icons:http://www.visual-case.it/cgi-bin/vc/GMapsIcons.pl

Contd.

Screen Overlays

Add an image to the Google Maps/Earth window. Could be used for whatever purpose you like. ScreenOverlay tag. overlayXY and screenXY line up the image to the actual map In this example, (0,1) (in fractions) means 0% of x (all the way to the

left) and 100% of y (all the way to the top). The upper-left of the image is lined up with the upper-left of the map. The unit can also be determined by pixels.

Size tag (obviously) controls size of the image. 0 means to maintain aspect ratio, -1 indicate to use native dimension. Using some other value makes the image that value. For example 0.2 with units on fraction makes the image take up 20% of that dimension.

Contd.

Network Links

Allows importing of KML, KMZ, and image files for ground/screen overlays.

Local or remote file Uses a Link tag Good way to split up large KML file into much smaller KML files. More

manageable. More interesting feature: can use scripts to generate KML data on the

fly. (PHP, Perl, etc.) Usually uni-direction data flow (server to map) but when using

“viewRefreshMode”, the map can pass the script information on what is being viewed (the LatLon box). Google Maps/Earth will call the script with a BBOX parameter. Look at the KML Tutorial for more information.

Contd.

Sources

http://en.wikipedia.org/wiki/Keyhole_Markup_Language

http://code.google.com/apis/kml/documentation/kml_tut.html#placemarks

THANK YOU