AlpineQuest & OfflineMaps

I have been playing with QCT maps in AlpineQuest Lite, and I was struck by how poor the image quality is when the image is zoomed out.

To demonstrate this I have taken screenshots of a QCT map (that I created myself from a scanned paper map), displayed at roughly the same zoom level in AQ Lite and, for comparison, in MM Tracker. I wondered if there was anything that could be done to improve it?

Here's the screenshot from MM Tracker:





And here's AQ Lite:

Hi and thanks for your feedback.
I never used MM Tracker so never compared both applications, but it's true that there is a big difference.
I think this is due to the fact that QCT maps in AlpineQuest are only fully read in lest level (the most detailed one), otherwise the quality is reduced in order to improve the display time.
In the 1.3.5 version available in few days, the zoom buttons set the map zoom at optimal scale values, so you may see a small improvement. I'll try to find some time to look if I can do something better, but I'm afraid it won't be so soon.
Best regards

Thanks for your response. Setting the map to optimal scale should be an improvement in cases where the user wants full zoom - I presume you mean with 1:1 pixel mapping between the screen and the image file.

The zooming in MM Tracker is fast and smooth, so it seems no loss of performance is necessary to get that image quality. My guess is that it's using some readily available library to do the high-quality zooming - the question, of course, is what??

I again.
Sorry for this late answer.

I know that the official MM application uses a low level library to decode maps, which is better for performances but won't work on any devices. Maybe that MM Tracker is also using this library. Unfortunately I can't use it because it's copyrighted, so not free of use.

The only thing I can do is to try to improve AlpineQuest decoder.
Have you seen a display improvement with version 1.3.5 ?

Best regards

Sorry, hadn't noticed the update...

I've tried it just now and it perhaps does look a little better, though still not as clear as MM Tracker.

I have some further information that might be helpful, though. I have established that when zooming out, MM Tracker only allows zoom levels of exactly 1/2, 1/4 or 1/8 full size, nothing in between. (The image snaps to one of these levels following the pinch operation.) It turns out that in the image I posted above, the map is exactly 1/2 size, a 2:1 pixel mapping

I can imagine that it would be relatively easy to create a crisp, sharp image when reducing the size by an integer factor, and maybe that is the secret of MM Tracker's clear zooming.

Yes, you're right that having a match of 1/1 between the map pixels and the display pixels would be perfect (or 1/2, 1/4, ... when zooming out).
But here is how AlpineQuest handle the map display:
1. The map is regenerated at fixed zoom values only, which don't depend on the current map (each value is the double of the previous one);
2. When generating the map at a zoom value, AlpineQuest chooses the level of the current map that best fit the current zoom value. If zoom value of this map level doesn't fit, it's stretch;
3. Between the fixed zoom values, the map is extended or compressed to simulate a continuous zooming.
(I hope I'm clear enough)

Depending on the mismatch between AlpineQuest fixed zoom value and the map zoom value, a loss of quality can happen at 2.
I'll have a look the ability of adapting the fixed zoom values with the current map zoom values.
Best regards

Hi,
Good news: the display quality of MemoryMap maps in version 1.3.6 has been improved.
The display should not be slower, even some times faster.
Best regards

Yes, that's a big improvement. But I've noticed (at least with my scanned map) that the image quality can change dramatically for a small change in zoom factor. I've illustrated this with the screenshots below; the second one is zoomed out from the first one by the smallest amount I could manage.

If there are some zoom levels that produce good images whereas others are more problematic, it would be good if the zoom buttons would step between the good levels. Or perhaps the pinch-to-zoom could be made to snap to the good levels. I'm just making suggestions.

Thanks your ideas.
Actually, the zoom buttons should already (versions 1.3.6 or more) step between good levels, for optimal quality:
- On low density screens, or if the AlpineQuest setting 'High resolution map' is not checked, the level zoom factors are set at x1 values (so 1 map pixel = 1 screen pixel);
- On high density screens with the setting 'High resolution map' checked, the levels ratios are set at x0.67 values (so 1 map pixel = 1 high screen pixel) (1 high density pixel = 1.5 pixel).

Between these values, the map is stretched or expended, and the next level is loaded on a particular threshold value (which correspond to x1.48 the lower level or x0.76 the upper one in your case). You should then have a low density screen.

On my screen-shots, the buttons set the levels at x0.67 ratios.
Let me know if you confirm this behaviour.
Best regards

Sorry for the delay in replying...

Yes, I can confirm the zoom buttons now step between reasonably clear images. Also I have found it is quite easy to use pinch zoom until a clear image appears, then release the fingers to keep that zoom level.

So I would say this is a big improvement overall. Thank you.

Thanks for the feedback!