3 ms·

I’ve often idly wondered if the reverse has been done: taking video capture of the shadows of objects over time and using the sun’s known position to generate m

by teeray 4y ago

I’ve often idly wondered if the reverse has been done: taking video capture of the shadows of objects over time and using the sun’s known position to generate models of the building. I was thinking that might be one clues some of the auto-generated 3D buildings use in, for example, Apple Maps.

defrost 4y ago
My guess would be "yes" - at the very least within the spooky photogrammetry community where many images from far away planes | sats can be compiled to produce "best guesses" on ground structures and routine movement. I stress "guess" as its essentially impossible to uniquely construct higher dimensional objects from sliced signals (or shadows) squashed to a plane (or lower dimension). Another application area for this is remote exploration geophysics that "scans" a airplane (or drone or helicopter or car etc) across a landscape recording magnetics, gravity, radiomentrics, EM return strength, etc in order to build a best guess model of deeper objects of interest .. copper deposits, iron, geological structure, etc. This is the arcane art of building 3D models from "shadows" .. but not the shadows you were thinking of teeray :)
- adolph 4y ago
  Muon Tomography is kind of like interpolating the interior structure of things using shadows, right? Cosmic ray muons have been used for decades to radiograph objects such as pyramids and geological structures. The technique of muon transmission imaging was first used in the 1950s by Eric George to measure the depth of the overburden of a tunnel in Australia. In a famous experiment in the 1960s, Luis Alvarez used muon transmission imaging to search for hidden chambers in the Pyramid of Chephren in Giza, although none were found at the time; a later effort discovered a previously unknown void in the Great Pyramid. https://en.wikipedia.org/wiki/Muon_tomography https://en.wikipedia.org/wiki/Muon_tomography
  - defrost 4y ago
    With a few additional twists .. rather than "simple" direct photon paths originating from an effective point source with some diffraction into Umbra, penumbra and antumbra you have a diffuse source (the entire visible sky) with varying strength from angle | amount of atmosphere and a spectrum of energies from primary high energy rays and scattered impact products of lesser energy. But, in essence, similar principle; a fixed position detector within a pyramid records the HE spectrum across a period of time and moved (or several detectors operate in unison) and the spectra are used used to reconstruct probable variations in density .. In airbourne radiometry the HE counts are recorded and calibration flights (lines at multiple altitudes) are performed to estimate the cosmic spectra coming in from above .. in order to subtract that from observed spectra to reach an esimate of spectra from the ground ( from U, K, Th .. radon, etc ).

by teeray 4y ago

defrost 4y ago

My guess would be "yes" - at the very least within the spooky photogrammetry community where many images from far away planes | sats can be compiled to produce "best guesses" on ground structures and routine movement. I stress "guess" as its essentially impossible to uniquely construct higher dimensional objects from sliced signals (or shadows) squashed to a plane (or lower dimension). Another application area for this is remote exploration geophysics that "scans" a airplane (or drone or helicopter or car etc) across a landscape recording magnetics, gravity, radiomentrics, EM return strength, etc in order to build a best guess model of deeper objects of interest .. copper deposits, iron, geological structure, etc. This is the arcane art of building 3D models from "shadows" .. but not the shadows you were thinking of teeray :)

adolph 4y ago
Muon Tomography is kind of like interpolating the interior structure of things using shadows, right? Cosmic ray muons have been used for decades to radiograph objects such as pyramids and geological structures. The technique of muon transmission imaging was first used in the 1950s by Eric George to measure the depth of the overburden of a tunnel in Australia. In a famous experiment in the 1960s, Luis Alvarez used muon transmission imaging to search for hidden chambers in the Pyramid of Chephren in Giza, although none were found at the time; a later effort discovered a previously unknown void in the Great Pyramid. https://en.wikipedia.org/wiki/Muon_tomography https://en.wikipedia.org/wiki/Muon_tomography
- defrost 4y ago
  With a few additional twists .. rather than "simple" direct photon paths originating from an effective point source with some diffraction into Umbra, penumbra and antumbra you have a diffuse source (the entire visible sky) with varying strength from angle | amount of atmosphere and a spectrum of energies from primary high energy rays and scattered impact products of lesser energy. But, in essence, similar principle; a fixed position detector within a pyramid records the HE spectrum across a period of time and moved (or several detectors operate in unison) and the spectra are used used to reconstruct probable variations in density .. In airbourne radiometry the HE counts are recorded and calibration flights (lines at multiple altitudes) are performed to estimate the cosmic spectra coming in from above .. in order to subtract that from observed spectra to reach an esimate of spectra from the ground ( from U, K, Th .. radon, etc ).