Folks, a bit of overlap between what I'm doing OSM-wise, so I thought I'd intrude with an undirected ramble and share some experience.
I'm the lead programmer on a free open source computer-aided-dispatch package that's based on GMaps, and I've started looking at what it wd take to get off GMaps in favor of OSM. Rationale is pretty obvious: The RACES community and others have been beating on me (gently!) for operation sans an internet connection. So, since the application is browser-based the plan is for tile storage at the local server, with OpenLayers JS also stored locally. Question #1 for me was re the hd storage requirements for a typical county-sized area. And, related, what's the zoom impact on storage needed. Most of the users I'm aware of seem to run about four tiles on-screen. To answer that, I picked my local AA County, Md as a test case, wrote a PHP script to download and store the tiles into a directory structure that OL works naturally with, and started the download. (I used zooms 9 through 17 as the range, with a 1-second sleep between files. Anyone interested in the script let me know.) Mebbe 60 hours later, I had me a directory with over 150k files and a storage requirement of over 800MB. With a fairly simple OL/PHP script and directory structure created by the download script, I now have me a PHP demo slippy-map application. (I've promised myself to avoid using 'proof-of-concept' terminology, but it applies.) A number of thoughts fall out: 1. That 1-second sleep is a major contributor to download time, given the surprising - to me - number of files. (Predictable, but ... .) 2. Zoom as tight as 17 is prbly too much of a good thing. Prbly 14/15 cd work OK, but I see it as a user choice. 3. Can prbly use every other zoom between the extremes. Mebbe worthwhile, mebbe not. FYI, Arnie Shore Annapolis, MD _______________________________________________ Xastir mailing list [email protected] http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir
