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Loading Tiled Imagery into Mappt

Last week I posted an article about Mappt supporting Compact Cache Bundles but did you know it already supports tiled imagery.  The difference between the two is that tiled imagery is exploded so each tile is it’s own image file.  There are three bit’s of information a tile needs to display on a google map.

  • The Level of Detail (LOD)
  • X position and
  • Y position

Tiling programs generally create a directory hierarchy to define these three properties.

Directory tile hierachy

Here the first directory is the LOD.  The next is the X location and the filename is the Y.   This is the most common structure but occasionally you will come across tiles with a single filename that contains the LOD, X and Y separated by an underscore character:

tile_hierachy_small

Mappt is capable of using both of these tiled images formats.  Just transfer the tiles to the tablet via the USB cable and make note of where they are located.   Personally, I load them into the Mappt -> Downloads folder and use ER File Explorer to  verify the exact path to the tiles.

es_file_explorer_path

Now select ‘Tiled Map Layer’ from the ‘Add/Load layer dialog’.

select_tiled_map_layer

Enter a name for the new layer and then type in the path to the tiles.

add_tiled_map_layer

The important part here is the fields surrounded by the curly brackets ‘{zoom}/{x}/{y}.png’ .  This part defines the structure of the tiles as discussed above.

Mappt now supports ArcGIS Compact Cache Bundles

We are pleased to announce that Mappt now supports ArcGIS Compact Cache Bundles.

Loading in your own satellite imagery is a common feature request for Mappt  and it’s not hard to see why.  Accessing your own imagery from a tablet gives GIS professionals and field workers the unprecedented power of being able to stand inside their data and perform ground surveys and analysis with total confidence they are looking at the correct features.  The inclusion of Compact Cache bundles is one of several new features that allows loading of custom imagery into Mappt and at the time of writing we are the only option outside of ESRI to utilize this format.  Mappt has been tested on the Sony XPeria Z with 30Gb of imagery and we have found the only limitation is the amount of free space on the SD card.

Mappt with a Compact Cache Bundle of ASTER satellite imagery.

Mappt with a Compact Cache Bundle of ASTER satellite imagery.

Compact Cache Bundles are a convenient format for tiled Imagery.   The biggest advantage of compact caches over an exploded format is that it eliminates the overhead associated with thousands of little files which means faster file transfer times and less space on disk.  This is a huge deal when transferring several Gigabytes worth of imagery onto a tablet.

Behind the scenes compact cache bundles act like a phone book.

compact_cache_bundle_hieracy

Up to 16,000 tiles for a particular level of detail are conglomerated into a single file with a .bundle extension.  This file has a companion with a .bundlx extension that acts like an address book for tiles.   Looking up the address for a tile has some computational overhead compared to an exploded format but fortunately we were able to optimize it to the point where there is no impact on Mappt’s performance.