You are hereForums / Android Software / Android Development / Implications of a Single Map Repository
Implications of a Single Map Repository
Topo maps and other maps used by BackCountry Navigator come in many small pieces, much like Google Maps. This isn't of particular concern to the user because they are all put together when viewing. .
Traditionally, BackCountry Navigator has stored these in the database file with the vector data - the tracks and waypoints - all in a .db3 file.
Recent research for BackCountry Navigator has changed some of these traditional models. The result is the choice to move to a single, file based repository for image data. Now, instead of one big file, it is in a large number of smaller files in a neatly organized directory.
There will continue to be a choice of datafiles for other data (waypoints and tracks).
What this means:
- There won't be a choice of db files for the raster (image) part of maps. There will only two choices - preview mode for online viewing, and offline viewing.
- The preview choice will lead to a set of all the map servers to choose from, as discussed in our section on preview.
- The offline choice will give you a choice of all the map layers that have been downloaded to date.
- You will continue to choose between datafiles for waypoints and tracks.
- There won't be any overlap when downloading, nor worry about loading the right map for a particular place.
The choice to preview a map or choose an offline file is therefore replaced with a choosing between preview and offline mode.
Choosing the Preview Map will bring up all available choices, while choosing Offline Map will bring up only those layers that have been downloaded.
There are a few challenges to this new approach, and we'll do our best to make them as smooth as possible:
- Maps are no longer in a single neat file for copying over.
- After a few sessions, your offline map is almost guaranteed to be disconnected - Meaning there might be a little bit of map here and some more over here. This already happened in .db3 files if more than one area was downloaded to it.
This will change the experience somewhat, but hopefully make it simpler in some ways. Comments are welcome.
Share This Page
I definitely like the idea of files and folders for the simple reason that I could replace the pictures with my own if I wanted to overlay something on a map. A desktop utility to download images and create file structure would be great to include with the Android software, without needing to include all of the features that the current desktop version includes. And if it could read in .db3 files and spit out the new folder structure, that would be useful too.
But I'm concerned with how fast the performance is supposed to be. A lot of files in a directory will be somewhat of a pain to sort out quickly. How does performance scale when the user decides to download full resolution for an entire state or region? Then there would be a massive number of files to wade through in a single directory, so you'll need to be clever!
I suspect you'll support the ability to change the base directory in the same way a current user can change .db3 file. In this way, it could be construed to be scaleable...
Good Luck. You may be the reason I buy an Android.
The research has proven that the images can be found from a file structure in about the same time as for a database and doesn't change much as the file gets huge. It did need some clever tricks.
It would not necessarily be simple for a human to wade through if you want to mark up an image. I admire someone with the patience to find the image they want to mark up.
I wasn't planning to let the average user change the base directory. Changing .db3 files has caused enough confusion for users in the past. Perhaps an advanced option.
My initial reaction to the single map repository was negative until I re-read the note and realized that waypoints and tracks would be managed separately. I think keeping those separate is very important.
So now my only concern is the potential growth of map data, and how to manage it. Things that can only grow eventually get too big...
David
It was a concern before and has only grown.
One possible way would be to mark rectangles for erasing much like you do for download.
Another way is to erase a whole layer.
Would it be possible to add a line in the "download maps of selected area to use offline" section where you select/create a folder for the maps you are downloading? The software could still show all map data together so you don't have to jump between files like the WM version. However when you use a file explorer or mount the phone on the computer you would see sub folders in the BCN data folder for each location you have downloaded tiles for. That way if tiles were downloaded for a location you are not likely to use again you could simply delete that folder. This would be easier than selecting tiles to delete with the rectangle selector or deleting layers. It would just be an additional level of folders in the data location (bcnav\tiles\mytopo\lost lake\layer # folders). Is this possible? Then in the example above, if I were not planning to return to lost lake I could just delete that folder from the SD card. My data file size is becoming problematic...