Question

The Google Maps API for a Polygon does not offer a drag method.

What would be an efficient way of implementing such a feature (i.e., sufficiently optimised so that it would not kill a four year old laptop)?

Thank you!

Answer 1

I found the Google Maps V2 Polygon Implementation to be very limiting for the needs I have had and solved it by creating a custom overlay. My group is currently stuck on IE6 so I have yet to migrate over to Google Maps V3 – but taking a quick look at the API shows that you could probably do a similar thing that I did in V2 with V3.

Essentially the idea is:

1. Create a Custom Overlay
2. Populate it with your own SVG/VML Polygons and attach a drag event to this custom polygon object

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Custom Overlays:

Here is some information to get you started on making your own custom overlay:

http://code.google.com/apis/maps/documentation/javascript/overlays.html#CustomOverlays

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Creating your own “Dragable” Polygon Object:

Once you get that down you’ll want to add your own polygons to the custom overlay instead of using GPolygons. I went through the painful process of learning SVG/VML and writing a library to bridge SVG/VML together – you could do that, but I would recommend starting by trying to use another library such as Raphaël.

http://raphaeljs.com/

Using Raphaël will save you a whole lot of time trying to figure out how to get cross-browser Vector Graphic (Polygon) functionality – and best of all it supports drag events already, here is an example from their library:

http://raphaeljs.com/graffle.html

Once you have a custom overlay and you are able to throw some Raphaël objects onto it the last step is to translate the coordinates you want from a Lat/Lng value to a Pixel value. This is available in the MapCanvasProjection of V3:

http://code.google.com/apis/maps/documentation/javascript/reference.html#MapCanvasProjection

You can use fromLatLngToDivPixel to figure out what the actual pixel values are for the points on your Raphael polygon, draw it, then add it to the overlay with a drag event.