Measure the Length of a Line on a Map after a MOUSE_MOVE Event

Question

One of the actions a user can perform using the ESRI Flex Viewer application is to draw a shape on a map (e.g. a line). Once the user is finished drawing the line, they will double-click the mouse which fires a DrawEvent.DRAW_END event. When this is fired, the line is measured using a call to an API function geometryService.project([geometryObject], spatialReference);.

I want to be able to call this function after a MouseEvent.MOUSE_MOVE event in order to measure the line on the fly, instead of only after the DRAW_END event. Unfortunately, the only two DrawEvents that get dispatched are the DrawEvent.DRAW_START and DrawEvent.DRAW_END. These ESRI classes are compiled classes, so I cannot make any changes to them.

Is there a way to add an eventListener to a MOUSE_MOVE event that can grab the current geometry of the line that is being drawn and call my API function to measure on the fly?

Thanks in advance.

Answer 1

I found a solution to this problem by circumventing the geometry service altogether and building a solution of my own. There is a great site that implements the Vincenty algorithm for measuring the distance between two coordinates. This is a very accurate approximation algorithm (within .5mm on Vincenty's earth ellipsoid), and is meant to be very efficient so that it can be used frequently (e.g. after a mouse moves).

Here's the basic steps to implement this:

1. Add an event listener to the map that listens for a mouse click
2. Once the mouse is clicked, convert the coordinates of the location of the click on the screen to map coordinates and add a listener to watch for a mouse move event
3. When the mouse moves, grab the coordinates of the mouse (as in step 2) and perform the Vincenty calculation. Create a custom tooltip on the map and add the Vincenty result to the tooltip text.
4. Upon double-click, send the result to the Geometry service and remove the tooltip from the map