Thread: [Announce] modRana: a flexible GPS navigation system
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MartinK is offline MartinK
2010-10-02 , 01:11
Posts: 1,548 | Thanked: 7,510 times | Joined on Apr 2010 @ Czech Republic
#236
I have just sent the newest V0.16-1 to the autobuilder, the main feature is, as promised, the experimental sqlite tile storage support!

What is this good for ?
As mentioned earlier in this thread and also in a related Mappero thread, tile take up more space than expected because each tile, even if only 500B in size, takes a whole 64kB cluster.
When using sqlite for tile storage, there are basically just 2 files per layer, not the usual tens of thousands of files and folders.

How to enable sqlite tile storage ?
Go to options->map and switch tile storage from files to sqlite.

Is it stable ?
It seems to work OK for both normal automatic tile download (including overlay) and batch download. But some errors can still can show up, so please report any unusual behavior when using this !

What about the 4GB maximum file size limit on FAT32 ?
When a size of the storage database reaches 3.7 GB, a new one is added. The is no limit on the number of storage databases.

How does it work ?
The tiles are stored in a sqlite database as blobs. There are two types of database files, lookup.sqlite and store.sqlite. The lookup file stores an database that indicates in which store the requested tile is. The store file has the actual data. Multiple stores should be numbered in ascending order, starting from 0:
Code:
store.sqlite.0
store.sqlite.1
store.sqlite.2
etc.
The storage database looks like this:
Code:
table tiles (z integer, x integer, y integer, store_filename string, extension varchar(10), unix_epoch_timestamp integer, primary key (z, x, y, extension))
The store databases look like this:
Code:
table tiles (z integer, x integer, y integer, tile blob, extension varchar(10), unix_epoch_timestamp integer, primary key (z, x, y, extension))
The only difference in the structure is that the lookup databases only stores the name of the store for given coordinates and the store database stores the actual blob.
Both also have a table called called version which has an integer column called v. There is a single 1 inserted, which indicates the current version of the table.

These database files are stored in the
corresponding layer folders.

When looking for a tile in the database, modRana first asks the lookup database and when it gets an answer, it asks the store described in the store_filename for the given coordinates.

Could this be used by other navigation apps ?
Why do you think I just roughly described how it works ?
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