(meteorobs) OT. -Profiling the Sandia Sentinel Camera's vision.

Larry ycsentinel at att.net
Tue Jun 16 02:45:21 EDT 2009


Arguably you are both correct. That is the proper & best way.

My problem from the very beginning is in your statement "Look up the 
altitude and azimuth of the Moon at each of  the image times, and fit a 
scale to it."

I lack both the computer skills and the software to draw "multiple & 
perfect" circles from a radius point(zenith), to any size corresponding to 
astrometric altitudes of a star, planet, or moon by dragging a mouse.

For that reason I finally gave up & searched omni-directional antenna 
radiation patterns and other circular scales including some logrithmics on 
line. Finding nothing..... I used a near perfect circlular linear scale 
found on line for a template which I could resize.

Maybe someone will do what I have not been able to accomplish in 3 years. 
Handyavi has the routine I needed in their trigger window option but the 
circular image is course and too blocky when enlarged.

YCSentinel


----- Original Message ----- 
From: "Chris Peterson" <clp at alumni.caltech.edu>
To: "Global Meteor Observing Forum" <meteorobs at meteorobs.org>
Sent: 2009/06/15 21:55
Subject: Re: (meteorobs) OT. -Profiling the Sandia Sentinel Camera's vision.


> I'd recommend calibrating your camera astrometrically. One extremely 
> simple
> way to do this is simply to take a bunch of images with the Moon in them
> from your history. Look up the altitude and azimuth of the Moon at each of
> the image times, and fit a scale to it. Azimuth is trivial- you only need 
> to
> find the pixel coordinates of the zenith and rotate around that; altitude
> depends on the lens characteristics. With the Rainbow L163 lens I use, the
> altitude is described by a cubic polynomial. Other fisheye lenses are 
> likely
> to be the same, with slightly different coefficients.
>
> Rigorously converting the Cartesian camera coordinates to accurate altaz
> values (and those into equatorial coordinates) is really the only way to
> determine with accuracy where a meteor is in the sky. Scales are okay for 
> a
> quick check, but not for any serious analysis.
>
> Can't the Sentinel software do most of this for you already? The data that
> Joe Chavez sends out has computed altitude and azimuth values for the 
> meteor
> in each frame.
>
> Chris
>
> *****************************************
> Chris L Peterson
> Cloudbait Observatory
> http://www.cloudbait.com
>
>
> ----- Original Message ----- 
> From: "Larry" <ycsentinel at att.net>
> To: <meteorobs at meteorobs.org>
> Sent: Monday, June 15, 2009 4:13 PM
> Subject: (meteorobs) OT. -Profiling the Sandia Sentinel Camera's vision.
>
>
>> The following measurements were found. The methods of arriving at this
>> data
>> will be explained below.
>>
>> The out-of-focus circular fringe area in the Sentinel cameras photographs
>> was measured to be 5.8 degrees BELOW true horizon at its first edges.
>> (-5.8). The actual fringe in focus could be a -6.3 but cannot be 
>> confirmed
>> without refocusing a Sentinel camera.
>>
>> True horizon (-0.9 actual degrees) is located close to the 10 degree
>> circle
>> on a linear Altitude scale of my own design fitted to an Azimuth scale 
>> and
>> made public.
>>
>> The Azimuth scale I constructed for general public use on Sentinel 
>> photo's
>> with a later added Altitude scale contains errors in altitude at lower
>> elevations due to what I believe is logarithmic compression of the lens.
>> This was anticipated at the time of the construction of the linear degree
>> circles. At 30 degrees elevation it is quite close, not more than 1.5
>> degrees error, measuring no more than 31.5 degrees maximum on a planet or
>> bright star at 30 degrees per an older astronomy program called Skyglobe.
>> Above 30 degrees the scale is quite precise and is accurate for all
>> intents
>> and purposes for a camera aligned to zenith.
>>
>> At the present time with this public scale fitted to Sentinel images, the
>> outside edge portion of the Azimuth scale is measured to be at a minus 
>> 0.9
>> degrees of true horizon. (-0.9). That bottom portion is scaled 10 degrees
>> as
>> a linear scale circle. It was necessary to use this Azimuth-Altitude 
>> scale
>> to perform the measures as clearly defined fixed points were not 
>> available
>> in the North-South direction for the Transit.
>>
>> The transit was leveled at the lower edge portion of the Sentinel camera
>> fish eye lens.
>>
>> Altitude measures were taken with a precision digital level attached to
>> the
>> transit as it deviated away from the fish eye lens in new azimuth
>> directions. Controlled tilting of the transit was measured for below
>> horizon
>> fixed points. The points used were: Camera lens, Roof top edge in S.E.,
>> amd
>> Roof gutter edge, all located below the true horizon but within the photo
>> vision of the camera. The gutter edge is located at the edge of the
>> out-of-focus camera perimeter. Local porch lights are slightly below that
>> edge and can be seen by the camera occasionally. This suggests -6.3 is
>> very
>> close for the maximum below true horizon aperature of the camera.
>>
>> These measures are very close but not precise due to out of focus targets
>> being used to compare to the Sentinel image taken this morning. If this
>> information is of some interest or use by others besides myself,  the 
>> task
>> is made worthwhile. Others may want to make their own measure to confirm
>> or
>> argue what I have found to be a workable.estimate.
>>
>> YCSentinel
>
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