[time-nuts] position determination over short distance

[Lux, James P]

On 12/5/08 3:32 AM, "Neon John" <jgd at johngsbbq.com> wrote:

> On Sun, 23 Nov 2008 20:26:52 -0800, "Lux, James P" <james.p.lux at jpl.nasa.gov>
> wrote:
>
>> There's a fair amount of F/OSS software from JPL available to do this sort of
>> calibration. It's used to calibrate cameras used on Mars rovers, among other
>> things. The target pattern for calibration is a bunch of big circular dots on
>> a background.
>
> URLs?
>
Google "JPL Camera Calibration" and you'll get a bunch of hits to various
technical reports. Once you have those, you'll have better search terms. A
lot of the software has been published in NasaTechBriefs as a TSP, too.

In general, you get an image of an array of big polka dots. The software
locates the centroids of the dots (which can be done with higher precision
than just looking for a single pixel point.. 0.1 pixel is apparently not too
tough, from what the camera guys tell me) (for instance, if you're doing
something like a star tracker, it's actually easier if the image is
defocused)
Then the measurements are turned into CAHVOR coefficients, which get used in
subsequent photogrammetric processing to rectify the image.


> I recently found this freeware open source on the net.
>
> http://tim-jackson.co.uk/area/index.html
>
> Caution: I've encountered this guy on Usenet where he has a bad tendency to
> substitute abject BS in place of fact when it's too much trouble to dig up the
> facts.  I'd inspect the sources closely before using, looking for shortcuts
> that don't work and pure old logic errors.
>
> It would do the job in this instance but I'm interested in a more generalized
> solution (without having to write it myself or buy anything) to pulling
> measurements from photos.
>
> I'd like to be able to take a photograph in which an object of known
> dimensions is included and pull other dimensions from the photo, including
> areas.
The JPL stuff would be more likely to be a library of dozens of routines
which you could string together to do this, rather than a handy point and
click interface.




>
> Any suggestions?
>
> John
> --
> John De Armond
> See my website for my current email address
> http://www.neon-john.com
> http://www.johndearmond.com <-- best little blog on the net!
> Tellico Plains, Occupied TN
> What do you call a blonde's cranial cavity?  Vacuum chamber?
>
>
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