Indeed, something like 25cm or better is typically shot from airplanes. I don't remember what the physical limit is for image quality given a reasonably sized spy satellite (iirc it's around the 20cm mark), but commercially at least, the high quality imagery is all airplanes. Governments often commission such planes to fly ~yearly at something like 10 cm, as well as commissioning height maps[1], but the very good stuff is not released to the public for privacy reasons. I think the best I've ever seen is 15cm.
The point clouds from those height maps alone, though, I already find to be quite interesting/revealing. You can see the contours of e.g. a tree exactly, even without having any imagery laid onto them: https://snipboard.io/tPsRBo.jpg
New Zealand regularly uses flying companies to take aerial imagery photos of most of the country, which is generally taken between 30cm and ~2cm, Land Information New Zealand (LINZ) then releases this imagery imagery completely free (CC-BY)[1,2] to the public and can be downloaded as GeoTIFFs [3]
I think LINZ decided that <0.05m might have some privacy issues due to being able to distinguish people in it, and have held back releasing some <0.05m or they may have reduced the quality of it.
disclaimer: I work at Land Information New Zealand
> but the very good stuff is not released to the public for privacy reasons.
You can buy the data, the agencies responsible for these data make some decent coin. Yes, they are expensive to obtain, but that is paid by taxpayers anyways, so it is kind of double dipping.
The entire area of Czech republic is available at 0,2-0,125 m per pixel for around ~100k EUR. Not unattainable for those who need it, but not hobbyist price either. For the neighboring Slovak republic, the ortophoto at 0,2 m per pixel is available for free.
Recently at an OSM meetup with the local government in Aachen (Germany), they mentioned that some imagery they shot was deemed too invasive and only used internally. I thought that was 10cm, but now checking what is available, looks like I was wrong! Probably it was 5-7cm then? Or maybe this was rather about the imagery available from different angles, so you can see into gardens from different directions?
In iD I see that indeed the PDOK imagery is now labeled 7.5cm, but checking that against the Belgian and German 10cm:
That is indeed awful, you're right. I remember that satellietdataportaal.nl or something like that allowed access to uncompressed files, maybe they're better. I'll see if I can find my old credentials and compare.
But yeah, compared to those 10 cm images, that can't be effective 7.5 cm/px.
Related: Apple Maps uses some data source that is ridiculously high res for my street. They've updated the image now sadly, but for a while I saw a gangly brown haired silhouette chasing two blonde haired kids across the street. I was super sure that was me and my kids; slanted shadows gave the right relative sizes, too. Cool and creepy at the same time.
For the Dutch railway network, ProRail has commissioned a set of aerial images shot from a helicopter at a height of roughly 190 m, which is ridiculously high-res and available for viewing here: https://twiav.nl/nl/luchtfoto_prorail.php
You can clearly make out individual paving stones or even the catenary wire, so the resolution must be somewhere in the 1 or 2 cm range.
But the imagery isn't from satellite data, is it? Must be from airplanes.