On 20/01/2015 10:38 AM, tagging-requ...@openstreetmap.org wrote:
Date: Mon, 19 Jan 2015 20:41:27 +0100
From: Peter Wendorff<wendo...@uni-paderborn.de>
To:tagging@openstreetmap.org
Subject: Re: [Tagging] Tagging road illumination quality
Message-ID:<54bd5de7.2070...@uni-paderborn.de>
Content-Type: text/plain; charset=utf-8
Am 18.01.2015 um 07:14 schrieb John F. Eldredge:
>You could use a light meter to measure how bright the light is. That
>isn't the only factor in the suitability of the lighting, but it is
>objective.
... provided that you measure on a dark night without moon and stars,
without cars driving on the road and no house next to it enlightened?
Even then:
Where do you measure the brightness? directly below the street lamp or
in the middle of two subsequent ones?
If that's the case, what's "brightness" when you compare different light
sources? which light temperature do you use as reference (which
wavelengths to measure at?, as the visibility of some colors are quite
different when looked at on yellow versus white street lamps (not to
mention the more subtile differences within those broad color categories).
regards
Peter
As a camera/light meter should try to reproduce the human eyes response
I'd think it would be a good approximation - certainly acceptable
compared to a subjective human assessment of 'bright/good/bad/average'.
When a gradient/slope is tagged 'we' place a number on it .. not a
subjective of 'steep/genital/very steep'. And additionally when the
light level is very low the human eye does not resolve colour but
reverts to black and white.
The moon and stars? Well the light meter has a 'noise floor' of a
minimum level too. I'd not be worried by the moon light unless it is
bright compared to the measurement, in which case the mapper is best
able to (subjectively) asses it,and may be come back a week or two
later. Even if not absolutely correct the number is still better than
the 'bright/good/bad/average'.
Having put forward an average of the brightest (under the light) and the
darkest (midway between two lights), I like to see (pun) consideration
of just using the darkest as that is where things are worst, and is
simpler for the mapper to take one reading.
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