Web Format > MapBox MB Tiles Tileset: Exported raster data disappears when zoomed in too close

Hi,

Can someone please advise me on the 'Zoom Level Setup' when exporting to Web Format > MapBox MB Tiles Tileset?

I have experimented a bit and found that the higher 'Number of Zoom Levels to Use' the further out you can zoom before the raster data disappears when viewed in ODK Collect e.g. 5 and the data disappears before I can see the extents - 10 and I can zoom out until the data extents is 5mm on my screen.

The problem is that the data disappears when I zoom in too close. Which means that if I were to mark the outline for a ground feature the raster baselayer would disappear at that zoom level e.g. tree, outcrop etc

Increasing to a higher Level setting e.g. 20 - 0.07 metres/pixel would take me all data to export and would probably create a huge file; and I even don't know if this would allow me to zoom closer anyway.

Can someone please enlighten me as to how to control this zoom level issue? Can I specific what specific zoom levels to export? Any other tips regarding MB Tiles would be most helpful e.g. can you only export whole tiles?

Thank you in advance.
Steve

Global Mapper v17.2 [64-bit].

Best Answers

  • MykleMykle Global Mapper User Posts: 385
    Answer ✓
    Steve,
    It looks like MBtiles displays are restricted to the zoom levels provided by the data, unless you have a viewer that provides for displays at zoom levels that are not included in the data file.

    The MBtiles viewer available at http://www.allmapsoft.com/ will display the available zoom levels on the title bar, and the display is limited to the zoom levels in the file.  

    ORUXmaps (android) will simply enlarge the tiles when zooming in further than the levels contained in the file.
    Global Mapper will do the same.  You just get larger and larger pixels when zooming in further than those contained in the file.

    It sounds like ODK Collect will allow you to zoom in further than provided in the data, but won't display data when the display zoom is out of range of those in the map file.

    Yes, you can wind up with large MBtiles files.  I have files as large as 200Mb and they display without problems in Android and Windows.

    I also have several MBtiles files that display different content at various zoom levels.  For example, a map containing zoom levels 13 to 17 displays topo maps at zoom 13 to 15, and a photomap at zoom 16 and 17.   Other maps change map comtent between 1:250K, 1:100K, and 1:24K topo maps as you zoom in or out.  Global Mapper has the options to create these overlays.  

    If you need high zoom levels, you may need to restrict your coverage so the resulting file size (and creation time) is acceptable.  You wind up with a collection of MBtiles files to cover larger areas.  That's about like my collection!

  • MykleMykle Global Mapper User Posts: 385
    Answer ✓
    There are options in Global Mapper to specify how border tiles are treated, either filled with your background color outside of your boundary and/or layer limits, or skipping tiles that are not completely filled.  Your use of PNG to make blank areas transparent is also useful. 

    For raster layers, the Raster Options dialog includes a tab for Map Zoom.  It does not include options related to zoom levels, which would be useful (I think that option is on their list).  So you will need a table of zoom levels and scales to guide your choices.  That means you should do some testing on a small area so you can sort out what you need to do. 

    I have worked with Open Street Map tiles as well as MBTiles, depending upon the requirements of different programs, so it can get complicated.  The MBTiles are used with ORUX maps (android), both on smartphone and tablet screens. 

    It is also useful to create source files from your master files for each sub-area that you work with.  Your time requirements will be reduced as well as the complexity of your project. 

Answers

  • sphillipssphillips Posts: 56
    Thank you for your reply Mykle - it is much appreciated.

    Your explanation makes complete sense. My tiles are over 2 GB in size as they cover a large area. So my next option is to export to a defined boundary; specifying only the minimum areas required. I am working under the assumption that GM will only export to the nearest full tile because if you saved as JPG you can see the background beyond the boundary you specify. I figured that you have to use PNG to make those areas transparent.

    I tried the MBtiles viewer software you mentioned but it couldn't handle the display of the tiles. Basically it didn't load them all and what it did load was all jumbled up like a giant puzzle ready to be rearranged.

    Could you kindly elaborate on how you are able to create map overlay for various zoom levels? What software are you viewing the tiles with? I'm going to trial GM Mobile for Android today to see if this is a better option.

    BTW, my apologies for the typos - got a new 'slim' keyboard and I'm still getting used to it!
  • MykleMykle Global Mapper User Posts: 385Trusted User
    Steve,

    One of my applications that has used the Open Street Maps format (directory tree of tile files) is changing to using the MBTiles format for more efficient file storage.  The developer has pointed out an application that provides a database view of the MBTiles files.  You don't get a view of the map, but of the gory details. 

    The open-source "DB Browser for SQLite" is available at http://sqlitebrowser.org/

    While the structure is interesting (sorta), a more useful summary is available by entering (all on one line) an SQL query:

    SELECT zoom_level, count(*) as count, min(tile_column) as min_col, max(tile_column) as max_col, min(tile_row) as min_row, max(tile_row) as max_row from tiles group by zoom_level order by zoom_level
  • sphillipssphillips Posts: 56
    Thank you again for your replies Mykle - I appreciate the time you have spent answering my questions. You have provided me with plenty of things to try and consider.

    As part of my research I tried TileMill to create the MBtiles, which has performed better - but has been harder to pick up. Exporting is quicker and I was able to export my MBtiles in 32 minutes (the estimated time was 8 hours so the estimated times take at least 10 minutes before they start to provide realistic estimates)

    I then tried GM Mobile (Android Beta) - which was extremely quick to export but very sluggish to navigate on the tablet (6 seconds to zoom or pan before the images reloaded). The files sizes are much smaller too at just 56MB compared with 2.2GB using MBtiles. When I tested the app none of the GPS tools appear to work at all which obviously defeats the purpose. Having said that maybe I haven't set it up correctly, but it is hard to tell with the lack of detailed help files. I was however able to manually create areas, points and lines. They say you can take photos but fail to see where this option is.
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