> On Nov 18, 3:31 pm, goFishy <[email protected]> wrote: > > > Hi all, > > > I'm looking to create an isochronous map for a catchment area of 2 > > hours or less. I've found an application that will do that, however it > > uses polygons that include areas covered by the sea and as far as I > > know, people can't drive over water. >
Interesting--I hadn't seen the Cartoo site. It doesn't seem very accurate, but you will have a tradeoff between accuracy and speed as Andrew mentioned. Here's another site with a similar goal, though it doesn't display isochrones, rather iso-distances: http://maps.forum.nu/gm_driving_radius.html That's Marcelo's site, and I used it as a base for building a fairly accurate set of driving regions based on both driving distance and time: http://www.healthypetmobilevet.com/area.shtml You can see the importance of getting a fairly accurate set of points if you look at the cyan region--a circle or oval would misclassify some significant areas. You can see part of the way I did it by looking at the following site, which I will obscure to keep out of search engines: www DOT healthypetmobilevet DOT com FORWARDSLASH testMaps.html I don't want random people to come across it, since it will exceed your IP's daily geocode request limit pretty easily. Also it takes a long time to run since there are so many requests. Since I only needed to generate the regions once, I just output the ending points and manually stitched them into polygons using OpenJUMP and adding a buffer to all points. If you just want isochrones, another place to look is: http://mapperz.googlepages.com/DriveTime_ESRI_GMAP.html But I think there's a reason that the page shows isochrones for 1 min, 2 min, and 3 min only. I'm sure the number of geocode requests required increases significantly for longer time limits if you want something that accurate. I looked there when writing my script but I needed both distance and time, since both cost money. You have to pay a driver by time and pay for fuel by distance! I like Andrew's thought about using polylines. In fact, I think the best way to do it is to start with something like Marcelo's, pruning back the routes until the time/distance is within your limit, then come back and search close to the pruned routes to increase accuracy. Take a look at Marcelo's code and you'll see how he prunes the route until he hits the distance limit. Look at his function shortenAndShow (). You can do the same thing with time on the GDirections() object (something like: dirObj.getDuration().seconds). I just went with brute force, but I'm sure you can get a rough set of polylines with something very much like Marcelo's code, then go back and search near those routes. In fact it might be best to go back again, with each pass a bit more accurate that the last. Writing something that elegant would take me much more time than just running the brute force approach once. Let us know if you implement something! -Brian -- You received this message because you are subscribed to the Google Groups "Google Maps API" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/google-maps-api?hl=.
