Underlay map versus Overlay map (Was: Basemap Rendering of place names and other inconsistencies)

[Harry van der Wolf]

Hi Rodolpho,

I write this to you but anyone having the knowledge can answer of course.

2013/11/10 Rodolfo <rodo...@gmail.com>

>> I have seen such a slider as well, for the transparency of the overlay online map.

Yes, but this is not an overlay online map, but an underlay offline map.
The difference underlay/overlay is important!
If your main map source is "offline vector maps", then an underlay raster map can be shown at full brightness by hiding the polygons of the vector map, so you see all roads and points of the vector map at 100% brightness over the 100% bright raster map.
If you use an overlay raster map, then the transparency balance between those can be adjusted, but both maps are displayed hazy (unless you move the transparency slider completely to the left or right to only show one of the maps).

This underlay vs. overlay map has been discussed earlier, but I can't find the topic. It's not written down in the wiki either (which I'm willing to do as soon as I understand what I'm talking (typing) about.
Based on what you explain above I understand the effect of underlay versus overlay map.

But what makes the difference between an overlay and underlay map? I know for example that the hillshades sqlite files are overlay maps.

Can I define a raster map as either underlay or overlay? So can I define the hillshade map also as underlay? And would that be useful?

Or when I hide the polygons does that automatically make an overlay map to an underlay map?

Where do I define that? in OsmAnd, in the map creator, or both?

If you even have more answers then the questions I just asked, please share them.

Harry

[Rodolfo]

Oh boy, this gets complicated :)
The hillshade layer behaves like a 4th layer, which sits between the base layer and the underlay.
So the order is: overlay, base layer, hillshade, underlay.
Although the hillshade map is a raster map, it offers transparency by setting its alpha channel to white.
The transparency slider only affects the topmost layer.
So if you activate a raster overlay map, the transparency slider affects the overlay transparency, thus slightly hiding both the base layer and the hillshade layer.
If you activate a raster underlay map, the transparency slider affects the base layer only (not the hillshade layer).
Ok, Harry, I confess, while writing this, I thought "Gooi dit maar in mijn petje" :))
Kind regards, Rodolfo

[Harry van der Wolf]

Thanks for your response.

I understand the alpha channel transparency, which is quite obvious when thinking about it.

But what makes a map an underlay map instead of an overlay map. The height maps you are using are underlay maps (as you describe it).

Is an underlay map a map without transparency? Therefore you need to undo the polygons in the base layer to see the underlay map "through" the base layer?

(On occasions I can be quite terrier like, as you see)

Harry

2013/11/11 Rodolfo <rodo...@gmail.com>

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[Rodolfo]

There is no technical difference between underlay maps and overlay maps.
You can use raster maps and vector maps in all the three map layers.
The different use has a lot to do with transparency. For the underlay map, transparency is not relevant, it is the lowest layer, you don't need to see anything through it.
For a higher layer, a map with "built-in" transparency has the advantage, that you can look through it to see the underlaying maps. So in general:
If you combine a vector map source with a another map without transparency, set the second map as underlay map (and hide polygons!).
If you combine a vector map source with a another map with transparency (like OpenSeamap), you can set the second map as underlay or overlay map.
If you combine a raster map source without transparency (like Microsoft Maps) with a map with transparency, set the second map as overlay map.
Hope this helps.

I also noticed while playing with the different combinations, that the app crashed a few times, but this could be lack of memory in my device. No exception log entry. Please help testing.
Best regards, Rodolfo

[Harry van der Wolf]

2013/11/11 Rodolfo <rodo...@gmail.com>

If you combine a vector map source with a another map with transparency (like OpenSeamap), you can set the second map as underlay or overlay map.
If you combine a raster map source without transparency (like Microsoft Maps) with a map with transparency, set the second map as overlay map.

And the question for the next round for the sunny vacation to the Maledives: Where/How do I set a map as underlay or overlay?
In the meantime I worked completely through the app and I simply can't find it. I can only find in Online maps (which I don't want to use) the option to use online, cached or base map as overlay / underlay. But I can find HOW to do that.

Harry

[Harry van der Wolf]

So I switched on "Online Maps" and now I can find it. And gosh: it also works for offline maps! It works especially for offline maps.

This is really a nice piece of logical, easy accessible, user-friendly gui programming :-).

I will experiment and extend the wiki when ready.

Thanks for your info.

Harry

2013/11/11 Harry van der Wolf <hvd...@gmail.com>