Make tiler zoom level configurable

[MertenF]

The zoom levels for generating 2d tiles is fixed to 5-21.
By adding following 2 options, it will be possible to configure the zoom levels.
--tiles-min-zoom
--tile-max-zoom

I have not yet tested these changes. Looking for feedback.

[Saijin-Naib]

This looks great!

Do you think you would be able to read the GSD for orthophoto/de and set the min-zoom to that?

Max I can't think of a reason to change...

I'm just musing if parameterless would be possible and meet your usecase?

I think many folks would love this!

[MertenF]

Dynamic min-zoom level, depending on the GSD, sounds interesting.
Keeping the max-zoom level hardcoded is fine by me. My use-case was getting deeper zoomlevels for more detailed projects. The current level is more than big enough.

I'll take a look into making the min-zoom dynamic instead of a parameter. Parameterless looks like the better choice.

[Saijin-Naib]

Thank you so much! I am sorry to put more work on your shoulders, but we struggle a bit with folks keeping track of all the parameters we already have, so when we can meet a need without adding one... It's a lot nicer for folks to work with.

I'm excited to see what you make!

[MertenF]

I've added calculations depending on the GSD. However in the splitmerge I could not find the GSD, so there I used the configured orthophoto-resolution argument.

[Saijin-Naib]

So, so cool! You should have a review by someone who can assess the code better than I shortly.

Thanks so much again for this amazing feature! You're going to make so many folks so happy.

[pierotofy]

Thanks for the PR @MertenF ! It looks like a useful addition.

I think we still need to enforce a more conservative maximum zoom level. 21 was chosen empirically because that's where things started to take too long to compute. I've run a test with 22 (which is still fine), but at 23 things got really slow. At 24 it almost took more time to generate tiles than to complete the rest of the pipeline.

I don't think we should go higher than 22 in any situation. Let's remember that ODM is not a replacement for post-processing. If one has a strong need to have super-resolution tiles, they can/should run gdal2tiles.py on the orthophoto manually outside of ODM?

[MertenF]

Each extra zoom level means that the amount of tiles goes times 5. So I guess it's not a big surprise that those higher levels need a lot more computation time. With that in mind, the limit that I've set (30) is indeed too high.

Level 22 results in an resolution of 3.73 cm/px, level 23 results in 1.86 cm/px.
I'm more inclined to have 23 as hard limit instead of 22. As this still means a substantial increase in my opinion. Level 22 will only be the case when both orthophoto-resolution and the GSD are less than 3.73. Which won't happen a lot I would guess?

What do you think?

[pierotofy]

I think 23 is reasonable. 👍

[pierotofy]

Looks great, thanks @MertenF !