Placement-map, zoom levels & basemap layers

1. What is the problem? Be very detailed.
The different basemaps in Collect have different zoom limits, is this documented somewhere, and are there other offline maps tips/tricks to be aware of?

I am trying to use a tileset generated from georeferenced layout drawings for a small area that requires higher zoom for precise location (approx 60x30m area) I have rendered tilesets out from Zoom level 0 to 25 (QGIS limit) but cannot access the highest levels.

On a 10" screen tablet, switching between different base layers, it appears that Google (streets / satellite / terrain) has a hard stop at level 20, USGS (topo), Stamen, Carto (positron) & OSM have a hard stop at level 21, Mapbox (streets) loads up to level 22 but will allow you to zoom further and pixelate instead of loading 23/24/25.

Mapbox appears to have 23 levels (0-22), search results for Google vary.

2. What app or server are you using and on what device and operating system? Include version numbers.

ODK Collect 2022.1.1
SM-T865 10" Samsung Galaxy S6 tablet

3. What you have you tried to fix the problem?

  • Render tilesets to different levels, try different basemap layers in Collect
  • Adjust tile dpi from 48 - 300. 200/300 appeared with very thick lines, 150 is slightly clearer, more readable to use than 96.

4. What steps can we take to reproduce the problem?

  • create tilesets that end at different zoom levels, attempt to display them on the different basemaps

5. Anything else we should know or have? If you have a test form or screenshots or logs, attach below.
I saw the mapbox layer not loading when offline thread - does this issue still exist in any form?

This thread appears related, but is quite old and has no replies

Should I try to generate a vector tileset, will this be clearer? Tippecanoe appears to have a zoom level limit of 22 also for generating pbf tiles, so will that also pixelate when zooming past 22?

I haven't been able to reproduce the Mapbox mbtiles layer not loading without "network" connection - #4 by seewhy so I don't know whether the identified bug has been fixed.

Regarding pixelation / zoom levels, in my experience, PNG format tends to give better results than JPG if you zoom beyond the stored zoom level, but I haven't tried adjusting tile dpi beyond 150, mainly to keep file sizes manageable. What I have found is that in some situations and on some devices when I try to zoom past the highest level of my mbtiles layer it disappears and the underlying vector data shows - I haven't found a reliable way of reproducing that problem, so haven't reported it.

The issue you will find with vector maps is that you can't style different layers (unless that has recently changed) so if you have a complex drawing, it may not help you and the line thickness might be greater than the difference from pixelated raster.

I'm not going to teach you to suck eggs on accuracy, but honestly I can't envisage needing a basemap so accurate in the field that I couldn't use my eyes to locate myself relative to a point on a map / drawing - but then if you are doing as-built QA work or setting out a construction site, ODK might not be the best mapping tool :slight_smile:

I can see what you're trying to do in terms of accuracy, and I'm not questioning that, but I'm not sure how widely applicable it would be to chase the highest zoom levels. I have experimented with basemaps of different types (usually taken from UK Ordnance Survey, but also 25cm resolution aerial imagery) and in the field I can't say the top end of zoom is much more help to me - and file size becomes a limiting factor for me.

Just to give some context, which might be of more general use than your specific case, I stop at zoom level 17 (~0.3m / pixel for my latitude) when generating basemaps for fieldwork - my built-in GPS only gives accuracy to 3m at best (with all the caveats of % certainty). This allows me, for example, to work on grids for data collection where points are 100m apart and I find I can navigate within 5m of a required point using placement-maps option for my geopoint. I would then probably use a photo if I needed higher degree of accuracy to relocate the point / quadrat. This works well with teams of enumerators.

I have recently started using a high accuracy gps for small projects and comfortably work to 0.5m accuracy (without RTK), and I could envisage using zoom level 18 (0.15m / pixel) if I was fully zoomed in.

I have been doing some drone mapping recently (and using ODK with the high accuracy GPS to map my Ground Control Points). After processing the data flying at 100m my map has a resolution of between 2 and 5 cm, so around zoom level 21, and absolute accuracy of (allegedly) 0.5m. But then in the field, I could use that only as a check that I'm within half a metre of where I think I need to be anyway, I suppose I could envisage trying to locate points within 10cm so at Zoom 22 that would be 10 pixels? But I'm potentially compounding my errors.

I am a strong advocate of sense checking my data - having a figure to 3 decimal places does not necessary mean it is accurate if the margins of error are above that - it becomes a false friend - especially if I am depending on data collected by someone else. My fear would be that using an ODK geopoint widget to check a location with centimetre accuracy could well be beyond its design limit and give enumerators an unhealthy sense of satisfaction and data managers a headache. It doesn't stop you recording the data at the high (e.g. RTK) accuracy now that @seadowg and others have developed that capability (thanks folks!). It might just be necessary to verify that data afterwards rather than in the field?

One thought though, having a scale bar on screen might be useful though to confirm how far beyond the maximum zoom of the tiles you've gone...

Sorry, long response, without a clear solution!

Thanks @seewhy for taking the time to provide such detail!

I am using PNG tiles currently, the filesizes are tiny due to the small area covered.

I did see the layer styling issue on vector maps, I can handle that as I'm only using monochrome layout drawings ex CAD

you're pretty close! It's condition inspection work, and I agree that this may not be the right tool, but it's the best tool I have right now, even though I'm trying not to treat ODK as a hammer and every problem as a nail.

GPS accuracy isn't a concern, as I'm looking to get more precise manual location placement, essentially 'redlining' a drawing, but the redline is then able to be used as GIS data (that can also be sense checked and adjusted to correct fat finger entry errors in the field).

Zoom level 22 is likely good enough for my needs, especially being able to zoom beyond 22 with pixelation, a hard stop at 21 is definitely not. This thread was more an exploration into what limits/quirks/tips were out there, I certainly wasn't expecting the mapping baselayers used to change!

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Worth trying the Galaxy Note with stylus. Fat fingers are a thing of the past - at least in terms of drawing on screen :slight_smile:

I've been using a Note 4 for a few years and find it really good for sketching in the field, and mapping is much easier to be precise, even in a waterproof case. The more recent versions of the Note are still too expensive for my grippy little wallet, but they do look pretty powerful with their bigger screens.

I don't blame you for trying to hammer every problem with ODK - I haven't found one I can't beat into submission, yet...

I just did some testing with the tilesets and geopoint/trace/shape:

  • Zooming past L22 on mapbox and placing points, I can easily show lengths of ~100mm increments, that is more than accurate enough for my needs.
  • With google maps the closest I can add two distinct points (i.e. points entered = 2, but two circles are shown and length >0m) is ~3.5-4m, there's some kind of arbitrary limit on this basemap that stops you placing them very closely
  • With OSM it's ~0.4m but placement accuracy is low.

I'm using Galaxy Tab S6 currently, I love the stylus (especially remote shutter)! And they're fairly affordable if you can scoop them up used.

There are still limits on how accurate my enumerators will be (wearing gloves, adverse environment.) so some post survey correction could be needed.

I think the latest Note 20 Ultra / Galaxy S22 Ultra would be a pretty ideal unit. Waterproof, stylus, very high resolution screen (so annotations preserve more pixels), and terrific cameras. But they are not cheap.