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I am looking for a solution that can enable the mobile browser load a collection of tiled images from the server and store them in local mobile device, then could display them even in offline mode.

I researched something by using CacheManifest and LocalStorage in HTML5, but it seems that they can only handle with a small amount of data. Besides, WebSql seems to be a potential solution, but I cant really understand how to acheive it.

Basically, the features I want to have is: load from the remote server while in online mode -> store them in local memory -> show them while in offline mode

thanks for any hints!

Simon
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2 Answers2

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I've had similar requirements on http://bluedot.mobi/td. Setting aside the caching issue for a moment, having a mapping framework that can be used offline is tricky - the best I'm aware of is the open source API OpenLayers.org. They have recently done significant work on enabling mobile device support. The big mapping APIs such as Google's javascript API restrict offline use and caching.

There is some work currently being done with OpenLayers to utilize either localStorage and/or websql. A working example is here. You can drill down to the source from there to see the different implementation methods.

Note that with OpenLayers you'll likely want to tap into the svn trunk to get the latest developments. It's a fast moving project.

DaveH
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Our open-source project at the recent iOS DevCamp (July) was focused on exactly this problem. We got pretty close to a workable solution:

https://github.com/pdxgene/iDCMapsLite

Highlights: - "online" tab browses maps (currently set to grab tiles from OpenStreetMaps, IIRC) - "save" saves map tiles to a Core Data store, and adds an "offline map" to the list in the second tab; - "saved maps" tab contains a list of saved maps. Selecting one grabs its tiles from the Core Data store and displays them.

Areas where work is still needed: - our intention was to recursively snapshot the map tiles, zooming both in and out. I believe we got one level down and one level out as a proof of concept.

I hope this helps. Feel free to try to make it work for you :-)

PDXGene
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