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Try reading the comment again. In that section they're talking about satellite photos, where they don't get precise control of the timing.
by mkl 4y ago
Try reading the comment again. In that section they're talking about satellite photos, where they don't get precise control of the timing.
- hammock 4y agoGot it thank you
- defrost 4y agoEven then it exposes an issue with delivery. I worked on earth scale digital mapping the late 1980s on a product that ultimately fed into Keyhole | Google maps | Hexagon. As a state we flew air photos every summer (and started with digitising these) and acquired various sat feeds through our ground station. Polar precessing orbits (MODIS, etc) do a full loop about the planet roughly every hour or so, and their orbit walks about the planet to maintain a roughly constant ground sun angle (~ sun-synchronous), returning overhead in 24 hours (or within the week, depending on interlacing patterns). The point being, we delivered high resolution images (digitised or, on request, blown up from good quality large format film negatives) over the urban areas from the summer surveys and ensured clear images OR we delivered sat imagery from a clear day (in the visual spectrum) or multi band spectrum data from whenever requested. A cloudy day can be easily rejected from many sat feeds - unless its areas such as PNG that are famously Obscured by Clouds [1] and required near ground helicopter survey work to map (fun times). [1] https://www.youtube.com/watch?v=8Di8-NzSMrg https://www.youtube.com/watch?v=8Di8-NzSMrg [2] https://www.youtube.com/watch?v=Ib-sqVe5mOM https://www.youtube.com/watch?v=Ib-sqVe5mOM