SQLite Forum

Jumbled image tiles?

Jumbled image tiles?

(1) By Tristan (tkh329) on 2020-05-17 17:07:25 [link] [source]


Please assume, correctly, I have zero understanding of the internal working of SQLite files.

I am struggling to understand why some apps and programs correctly display SQLites I export from raster data, while other apps and programs show the tiles in odd locations at incorrect zoom levels. Why is this?

For more detail, I use a GIS program, Global Mapper, to export raster data into SQLite files, normally PNG tiles. I normally the SQLites in OsmAnd, an open source mapping app for Android. OsmAnd displays SQLites from earlier versions of Global Mapper correctly. SQLites exported from later versions of GM do not display correctly in OsmAnd. Locus Maps for Android displays both earlier and later exports correctly.

I have the same experience with MBTiles. OpenCPN for Android does not display later version exports of MBTiles files correctly while Locus Maps does. Is it the same problem?

Thank you for your time!

(2) By Warren Young (wyoung) on 2020-05-17 18:22:12 in reply to 1 [source]

I would guess that you're corrupting the PNG data on either import or export, and that some of these apps have more tolerant PNG decoders than others.

You're going to have to give a lot more detail if you want more than guesses, though. For instance consider sharing a single-row SQLite DB containing a tile that you find doesn't display correctly in some apps. Then we can at least help you test the file data's compatibility.

(3) By Keith Medcalf (kmedcalf) on 2020-05-17 18:26:56 in reply to 1 [link] [source]

Yes, the root cause is the same. The Applications are "buggered up".

SQLite merely stores and retrieves data. Sort of like a secretary and that secretarys' filing cabinets. The secretary is not, however, responsible for the contents of the files stored and retrieved. If the boss requests a bunch of files to make a picture board and it looks like shit, that is not the fault of the secretary. It is the fault of whomever prepared the contents of the files for the secretary to store in the first place or who processed the files after the secretary retrieved them.

The Application diddles the data for storage and then diddles it again for display. It is the diddling (in the Application) that is buggered up.

(4) By Tristan (tkh329) on 2020-05-18 01:55:59 in reply to 1 [link] [source]

Thank you for the replies. I'll put together a small file to share.