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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 s
by lucgommans 4y ago
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 https://snipboard.io/tPsRBo.jpg
[1] For those that can read Dutch, how the Actueel Hoogtebestand Nederland is made: https://www.ahn.nl/ahn-the-making-of https://www.ahn.nl/ahn-the-making-of
- iwillbenice 4y ago
- isoprophlex 4y agoDoesn't PDOK provide 8 cm resolution photos of The Netherlands?
- lucgommans 4y agoRecently 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: PDOK 7.5cm: https://snipboard.io/fbWqYM.jpg https://snipboard.io/fbWqYM.jpg AIV Flanders 10cm: https://snipboard.io/Ahn4lJ.jpg https://snipboard.io/Ahn4lJ.jpg NRW (Germany) 10cm: https://snipboard.io/RpT3vA.jpg https://snipboard.io/RpT3vA.jpg PDOK's looks awful, much worse than 10. Maybe some regions are available in a higher resolution?
- isoprophlex 4y agoThat 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.
- iggldiggl 4y agoFor 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 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.
- vetinari 4y ago> 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.
- denhaus 4y agoAs someone who doesn’t know anything about this particular data, how would I go about obtaining that Slovak republic data for free?
- carl_dr 4y agoThe eastern part of the country isn't available yet (April 2023), but the downloads (and supporting information) for what is available is here : https://www.geoportal.sk/en/zbgis/orthophotomosaic/ https://www.geoportal.sk/en/zbgis/orthophotomosaic/
- blacha 4y agoNew 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 [1] https://basemaps.linz.govt.nz/?i=hawkes-bay-urban-2022-0.05m#@-39.4796659,176.8716430,z12.0483 https://basemaps.linz.govt.nz/?i=hawkes-bay-urban-2022-0.05m... [2] https://basemaps.linz.govt.nz/?i=christchurch-urban-2021-0.05m#@-43.5315130,172.6348627,z12.3819 https://basemaps.linz.govt.nz/?i=christchurch-urban-2021-0.0... [3] https://data.linz.govt.nz/layer/106915-christchurch-005m-urban-aerial-photos-2021/ https://data.linz.govt.nz/layer/106915-christchurch-005m-urb...
- eru 4y ago> [1] For those that can read Dutch, how the Actueel Hoogtebestand Nederland is made: https://www.ahn.nl/ahn-the-making-of https://www.ahn.nl/ahn-the-making-of Google Translate handles it just fine. Interesting!