Developer's Guide - MapGuide Open Source - OSGeo

Introduction
Digitizing
Redlining
This chapter describes digitizing (capturing the user’s clicks on the map and
converting the locations to map coordinates) and redlining (drawing items
such as lines or rectangles on the map in response to the user’s clicks).
The Viewer API has a number of functions for digitizing user input. For an
example of how these can be used, see task_pane_digitizing.php in the
digitizing_features directory in the Developer Guide samples.
In this example, if the user clicks the button to digitize a point
the script calls the JavaScript function
function DigitizePoint() {
parent.parent.mapFrame.DigitizePoint(OnPointDigitized);
}
which in turn calls the DigitzePoint() method of the Viewer API in the map
frame. It also passes the name of a callback function, OnPointDigitized, which
is defined in the current script. DigizitzePoint() calls this function after it
has digitized the point and passes it the digitized coordinates of the point.
You can use this callback function to process the digitized coordinates as you
wish. In this example, the script simply displays them in the task pane.
function OnPointDigitized(point) {
ShowResults("X: " + point.X + ", Y: " + point.Y);
}
There are three main steps involved in redlining:
1 Pass the digitized coordinates from the client to the server.
2 Create a temporary feature source. This will be used to draw the lines on.
3 Create a layer to display that temporary feature source.
90 | Chapter 6 Digitizing and Redlining