[_xnmw]

Pretty insane for you to believe that a foreign country from afar could produce mapping data with the same degree of accuracy, detail and realtime freshness as a local provider on the ground. Of course there's military value in protecting mapping data from foreign adversaries, at the very least it adds a a time delay and some uncertainty to the data. It also probably makes it harder for some unsophisticated terrorist to strap a consumer GPS to a stock drone and accurately hit a target.

[mopsi]

There's no need to speculate. Even with 1960s tech and no physical access, the US military somehow managed to produce really good maps of the USSR, superior to those that were available to the public. So ironically, the intentional inaccuracy of USSR-made maps affected domestic users the most.

In 2024, with satellites producing imagery in ~10 cm resolution, the most important factor determining the quality of maps is probably the amount of money available for analyzing satellite imagery into maps, and you definitely can't hide militarily important features like roads, railways, bridges and buildings.

[planede]

The images might have ~10cm resolution, but that doesn't necessarily mean that there can't be larger scale systematic offsets and other distortions for larger tiles.

I recently learned that satellite images are often corrected to match known maps.

https://www.youtube.com/watch?v=PVemGumEEgo

[_xnmw]

Sure, but there's a limited amount of information available from a satellite image. It's hard to tell what's going on inside a building, for example.

[dumpsterdiver]

This is why I believe the policy of obfuscating strategically important sites in map data is counter productive. If you overlay the Chinese provided obfuscated mapping data over mapping data obtained by your own military apparatus, the "obfuscated" portions of the Chinese data suddenly become "highlighted".

[zambal]

The subject is the ability to make accurate up to date maps out of satellite imaginary. I fail to see how this is a counter argument against that.

[pertymcpert]

And a domestic government approved mapping service will tell you what’s going on inside a building? Why are you moving the goal posts?

[sumedh]

> Pretty insane for you to believe that a foreign country from afar

US spy satellites can take sharp pictures which look they were taken by a drone is flying close to the ground.

[chefkd]

Could something like the SR-71 or hot air balloons be used to make accurate maps? In my head satellites which are expensive only follow one orbital path but a plane or a balloon can cover multiple regions

[yencabulator]

Consider a Hubble-size lens at a distance of 200-1000 km. If I did my quick math right, turning just 20 degrees moves the focus by up to 350 km on the ground. And typically orbits have a pattern of gradually shifting, so the next orbit will capture a different slice.

Reconnaissance planes were largely obsoleted by satellites when digital cameras were invented (before that, satellites physically dropped film to ground to be developed), and as Russian anti-air missiles got better. The primary use for optical reconnaissance planes these days is for up-to-the-minute coverage of rapidly developing situations, such as in war, where the next satellite flyover might not be until several hours later.

(RF & radar reconnaissance planes are very important to modern warfare.)

[chefkd]

Whoa so many mind blowing facts. Does the orbit change or does the lens rotate? If one knos the rotation degree can the total number of satellites it would take to cover the entire earth be calculated?

[yencabulator]

Here's an example of an non-"changing" orbit goes over different parts of the planet over time: https://www.scienceabc.com/eyeopeners/why-do-satellites-orbi...

It's highly unlikely that a satellite-based telescope would rotate/turn the lens. Turn it relative to what? It's in 0g, there's no part that's held in place by friction to the ground. Any rotating joint would make the two sides move in opposite directions. And if you think about that, let one side be much smaller, and allow rotating by multiple turns instead of just 0-360 or such, you might just invent the gyroscope.

They turn the whole satellite with gyroscopes (flywheels) and/or propellant.

[standing_user]

define "afar" given the level of resolution of the US spying satellites

[pertymcpert]

Pretty insane of you to not understand how good modern military satellites are.