[closed] Auto Caching Map?

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VaTrailRider
Posts: 15
Joined: Thu Jul 28, 2016 1:23 am

[closed] Auto Caching Map?

Post by VaTrailRider » Sun Aug 07, 2016 3:24 pm

I just want to make sure I am understanding this correctly that the app automatically caches maps you view in the app. Is this correct? To cache a map area to my app for offline use, I simply have to view the relevant area and zoom in and out to the levels I need and it is automatically saved to the app for me to use and view offline? If so, what is the difference then, between doing that and using the "select and save an area" option?

Thanks!

ds47uk
Posts: 86
Joined: Sat May 04, 2013 8:40 am
Location: Durham, UK

Re: Auto Caching Map?

Post by ds47uk » Sun Aug 07, 2016 6:42 pm

You are correct - and each method has its advantages but the end result is the same.

If you are wanting to view a path and a few metres either side of it, then "walk along" that path at the resolution you want (making sure to wait for the map to fully download at each point). It will cache THAT LEVEL ONLY.

However if you want the maps for an area you will be visiting, then the "select and save" is by far the better method. It will store all the levels you choose for the area you select, so obviously the size of the cached data will be larger. The advantage is you can zoom in and out as required.

Both methods use the same cache, so you can mix and match.

VaTrailRider
Posts: 15
Joined: Thu Jul 28, 2016 1:23 am

Re: Auto Caching Map?

Post by VaTrailRider » Sun Aug 07, 2016 7:35 pm

I think I understand the difference now. Thank you.

Psyberia-Support
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Re: Auto Caching Map?

Post by Psyberia-Support » Mon Aug 08, 2016 8:56 am

Thanks a lot ds47uk for this great answer!
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Yemble
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Re: Auto Caching Map?

Post by Yemble » Mon Aug 08, 2016 9:20 am

If you are caching maps for the long term, you would be well advised to keep a backup copy of the .../cache/custom-maps folder on a separate storage device (eg. a second SD card or laptop, etc.). The map cache can grow very large, especially for detailed topo maps such as OSGB.

If you do not have a backup and your map cache gets corrupted, then you would have to start from scratch, with the potential for many hours of downloading in order to get back what you have lost.

T2D
Posts: 18
Joined: Sun Jul 03, 2016 10:24 pm

Re: Auto Caching Map?

Post by T2D » Mon Aug 08, 2016 4:58 pm

Are cached maps ever automatically refreshed?

From here: http://www.alpinequest.net/en/help/v2/maps
When the same area is displayed again, the application will use the stored data instead of downloading it again (unless the stored data is too old and a new version can be downloaded).
"unless the stored data is too old and a new version can be downloaded"

Does that mean:

1) Automatic.
When a user displays a cached map-tile, AQ detects if it is "old" and automatically retrieves a fresh copy.

2) Manual.
User manually clears the map-cache so AQ is obligated to retrieve a fresh copy.

Yemble
Posts: 333
Joined: Sun Apr 28, 2013 5:02 pm

Re: Auto Caching Map?

Post by Yemble » Mon Aug 08, 2016 6:11 pm

I believe that each map tile has an expiry date, set when it is downloaded, after which it will be refreshed from the source server if AQ is in on-line mode. However, it is not clear what the expiry interval is for any given on-line map. I do not believe that AQ has any control over this. Note that a map tile will only be updated if it is actually displayed and then only at the displayed zoom level. So it is not the same as the download area function in AQ which can apply to all zoom levels.

Psyberia-Support
Site Admin
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Re: Auto Caching Map?

Post by Psyberia-Support » Tue Aug 09, 2016 8:36 am

Yes there is an "expiry" date for the tiles. This delay is defined at the map level. From the "Available maps" list, you can long press a map, select "Details" and check the "Update" line. "3M" means 3 months for example.
The application will (try to) automatically update tiles older than that after displaying them (tiles are not updated if they are not displayed).
Also, the "Store complete area" tool will never update tiles by default (it just skip the tiles already available, no matter their ages). You need to check the "update data already stored" option to update the tiles using this tool.
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ds47uk
Posts: 86
Joined: Sat May 04, 2013 8:40 am
Location: Durham, UK

Re: Auto Caching Map?

Post by ds47uk » Tue Aug 09, 2016 9:10 am

I think Yemble's advice about creating backups onto a secondary SD card or (preferably) PC storage is a good point to remember.

There is no way of telling if map providers decide to change their servers or access permissions, and if a map tries to update itself in these circumstances, I suppose there is the possibility of getting the dreaded red crosses or blank tiles. These would then presumably auto-cache themselves and overwrite the good data.

If you have a backup, then the "update-delay" field in the AQX file can be edited to NEVER update. and your backup maps can be moved back onto your Android device.

David

Yemble
Posts: 333
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Re: Auto Caching Map?

Post by Yemble » Tue Aug 09, 2016 10:41 am

ds47uk wrote: There is no way of telling if map providers decide to change their servers or access permissions, and if a map tries to update itself in these circumstances, I suppose there is the possibility of getting the dreaded red crosses or blank tiles. These would then presumably auto-cache themselves and overwrite the good data.
I can confirm that this type of cache corruption can happen from personal experience :o

VaTrailRider
Posts: 15
Joined: Thu Jul 28, 2016 1:23 am

Re: Auto Caching Map?

Post by VaTrailRider » Fri Aug 12, 2016 11:25 am

Thank you, everyone, for all the great info! I do always keep a backup of things that are important to me, and I have a folder on my SD card for all of my trips and Maps. :)

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