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Hi Frank,

> You are at the center of the universe: Silicon Valley.

Ha!

> The time is always the largest uncertainty in this sort of fix, both because
> your camera's clock (or whatever you used to time the photo) and the
> satellite's mean longitude could both be in error by a second or two.

Yes.  The camera unfortunately writes its EXIF timestamp only to the
nearest second; after taking the photos I took one more photo of my
PC's NTP clock as a calibration (the camera turned out to be 14
seconds out).  So the error could be as much as two seconds.  Better
would be a little optical gadget that inserts an LED time display into
the actual exposure, or, simpler, an external device that records the
shutter signal.

> ... you're along an LOP running between 37.54°N, 122.34°W and 37.35°N,
> 122.08°W. Picking a middle point, I'll go with 37.43°N, 122.19°W

Very close!  Attached is a kmz with the GPS position and the estimates
you give.  About 380 meters from the LOP and about 415 meters from
your fix.  I think much of this 400 meters must be ISS orbit error.

> ... Then I realized that this motion is the composite of the
> actual motion and the motion of your camera during the exposure.

It would be nice for the camera to remove this ambiguity by
interrupting the exposure for a few milliseconds near the end of the
500-ms main exposure.  That way there would be a little dot indicating
the endpoint, for both stars and satellite.  Yet another reason why
these cameras need to be fully general-purpose platforms rather than
just photo gadgets.  Don't get me started on the utter inadequacy of
the camera APIs for Android and iOS.

> By the way, a digital camera/space station/Internet determination of an
> observer's position independent of GPS calls for a press release, wouldn't
> you say?

I think it can certainly be said to be fully independent of GPS:  the
ISS orbit would be determined from the space radars.  Now, no doubt
ISS carries GPS receivers; is that data available anywhere, so that a
truly precise orbit can be used?  In my opinion the various pieces of
space junk (rocket bodies, defunct satellites) should be instrumented
with GPS receivers and the real-time orbits disseminated for the
benefit of optical observers :-).

Cheers,
Peter

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