Supported Zoom Levels for OpenCPN

[bradfordharley]

Good day all. I have been doing drone mapping to make mbtiles of my favorite anchorages. I find the increased resolution invaluable for understanding bottom topography as well as shorline not just for navigation, but snorkeling, spearfishing etc. I have successfully made maps that I'm happy with for my favorite anchorages, however I cannot go above zoom level 19. Anything 20 or above makes the scale all wrong and it ends up not displaying properly. For example, zoom19 provides a 1:1000 scale. Zoom20 is 1:156412 which is obviously wrong. I looked in the mbtile via SQLite and see nothing defined as scale, so I assume it is a calculated value from opencpn.
Anyone experience this and/or have any suggestions?

Thanks in advance
Brad Harley
SV Perspective.

[nohal]

Post a sample, please. We have probably never seen a tileset with such a high maxzoom.
There of course is nothing like a scale for mbtiles, the value shown is an estimation calculated from the content.

[bradfordharley]

Originally Posted by nohal

Post a sample, please. We have probably never seen a tileset with such a high maxzoom.
There of course is nothing like a scale for mbtiles, the value shown is an estimation calculated from the content.

Attached is a zoom level 19 (works) and a zoom level 20 (doesn't scale correctly)

Thanks in advance. If you want me to generate any other zoom levels, just let me know.
I can't attach an mbtile, so here is a link.
https://www.dropbox.com/sh/rxcslbq8l...Z-dxLxGsa?dl=0

[bdbcat]

bradfordharley...
To save some time searching, what is the geographic location of these tiles?


Thanks
Dave

[LeaseOnLife]

Originally Posted by bdbcat

bradfordharley...
To save some time searching, what is the geographic location of these tiles?


Thanks
Dave

Mexico Pacific Coast: center of tiles is ~
19° 32.0037' N 105° 05.1340' W

[bdbcat]

lol...
Thanks


@bradfordharley...
The tiles look fine to me.
Can you post a screenshot showing errors or other incorrect information that you are seeing?


Thanks
Dave

[bcn]

The place (more or less) as S-57/oeSENC from the future Mexico-Pacific set....
Chart scale is 1:8000

[LeaseOnLife]

Originally Posted by bdbcat

lol...
Thanks


@bradfordharley...
The tiles look fine to me.
Can you post a screenshot showing errors or other incorrect information that you are seeing?


Thanks
Dave

Doesn't work here.. for me: z19 shows, z20 does not. It is in 2 separate files and once I excluded all other tiles but z20, then no tile is shown.

[bradfordharley]

Here are screenshots showing the zoom. I can actually view the map, it just shows in the wrong order...as in the google sat images will squash it as I zoom as openCPN thinks a zoom level 18 google sat image is 1:4000.

{edit} as an aside, running latest on windows 10. I think it will do the same on the pi, but haven't actually tried... But could if it's of value.

[bradfordharley]

And here is a screenshot of Zoom 21 which is pretty close to native resolution of my geotiff and the scale actually increases rather than reduces.

aside 1: I have tried this with two different apps that make mbtiles, map tiler and mapc2mapc and the behavior is identical. I expect this if the scale logic is within opencpn.
aside 2: Not related, but if curious my workflow to create these is (manual) drone survey, processed with webodm to create a geotiff, then mapc2mapc (or map tiler) to make mbtile. Great for anchorages of 'interest' where I want high resolution and can shoot on a calm day. Shows bottom formations--good for rocks. Rocks are bad for the boat, good for fishing.

[bdbcat]

bradfordharley...
OCPN 5.6.0 as released supports zoom levels up to Z19. It is a simple change to support Z20, or even Z21. No one up to now has asked for this capability. I have tested this, and it seems to work fine. Could be added to a future release.


However, and just for my edification: With your uploaded tileset, I see no practical difference on-screen between Z19 and Z20. In the max OPCN rendering scale of 1:800, they look the same, on my gear.
And if that is so, why use Z20, which is 4 times the size of Z19, for equivalent geo area coverage?



Am I missing something?
Dave

[Baikal]

19 zoom is enough!
20, 21 zoom is relevant not for satellite images, but for aerial photographs of a local small area, in such images the detail and clarity is very high. You will have to take such pictures yourself from a drone.

[bradfordharley]

Originally Posted by Baikal

19 zoom is enough!
20, 21 zoom is relevant not for satellite images, but for aerial photographs of a local small area, in such images the detail and clarity is very high. You will have to take such pictures yourself from a drone.

With all due respect, read my post. These are drone surveys.

[bradfordharley]

Originally Posted by bdbcat

bradfordharley...
OCPN 5.6.0 as released supports zoom levels up to Z19. It is a simple change to support Z20, or even Z21. No one up to now has asked for this capability. I have tested this, and it seems to work fine. Could be added to a future release.


However, and just for my edification: With your uploaded tileset, I see no practical difference on-screen between Z19 and Z20. In the max OPCN rendering scale of 1:800, they look the same, on my gear.
And if that is so, why use Z20, which is 4 times the size of Z19, for equivalent geo area coverage?



Am I missing something?
Dave

Good question, and I don't really think you're missing anything. At Z19, it's 91%(according to my maptile program) of the resolution of my image file and there are very slight differences than Z20.
That said, I purposefully scaled down my source image to try and find a balance with size. This example shows the limit of the source image in going to/beyond Z20, but I can easily increase resolution of the source geotiff as my original survey was originally 4k. If it's an easy program change, going up to Z21 or 22 should suffice for anything I could imagine imaging.

As an aside, I would happily provide sources images and re run processing of the surveys if you want different image resolutions etc. to play with.

I do appreciate the responsiveness and discussion.
Brad
SV Perspective

[bdbcat]

Brad...
As I recall, the main reason we originally stopped at Z19 was because neophyte users of the tile preparation software supposed that more resolution must be "better". And so OpenCPN was presented with truly gigantic tile sets, covering enormous geo areas, which could not possibly be rendered at full detail on any reasonable system. Tile sizes of gigabytes....

We stopped at Z19 to save everybody the trouble of trying to load unusable tile sets.
Over time, tile prep code users have learned the practical limits of mbtile usage, and these days we are mostly seeing small-ish photo overlays, instead of chart images. That's good.


In your use case, I assume you will limit the geographic area sufficiently to manage tile set size....


We will increase to Z21 on next maintenance release.


Dave