RE: Sun path polar chart generator

[Valentin Hristov]

The link given by Peter is wrong. The file is
http://www.math.bas.bg/complan/valhrist/az-ht.bas
A screen shot is attached.
I hope this will help!
Valentin Hristov

From: sundial  on behalf of Peter Mayer 

Sent: Wednesday, March 1, 2017 12:43 AM
To: Dan-George Uza; sundial@uni-koeln.de
Subject: Re: Sun path polar chart generator


Hi Dan,

Valentin Hristov wrote a DeltaCad program Az-Ht.bas which does much of what you 
want, I think.  With a bit of modification, you could put the Oughtred dial 
parts into a separate layer.  You can down load Valentin's program at: 
www.math.bas.bg/~complan/valhrist/az-ht.bas


best wishes,

Peter



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Re: Sun path polar chart generator

[Peter Mayer]

Hi Dan,

Valentin Hristov wrote a DeltaCad program Az-Ht.bas which does much of 
what you want, I think.  With a bit of modification, you could put the 
Oughtred dial parts into a separate layer.  You can down load Valentin's 
program at: www.math.*bas*.bg/~complan/valhrist/*az*-*ht*.*bas*


*
*

best wishes,

Peter*
*





Hello,

I'm looking for a freeware solution to generate customizable polar 
sun path charts in vector format. The software should be able to 
display sun paths for a custom time interval (like daily, weekly) and 
feature analemma curves for standard hours. Any help will be appreciated!


Dan Uza





--
Peter Mayer
Department of Politics & International Studies (POLIS)
School of Social Sciences
http://www.arts.adelaide.edu.au/polis/
The University of Adelaide, AUSTRALIA 5005
Ph : +61 8 8313 5609
Fax : +61 8 8313 3443
e-mail: peter.ma...@adelaide.edu.au
CRICOS Provider Number 00123M
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Re: Dial face colouration

[Steve Lelievre]

John, thanks for the clarification, and your patience with my questions.

All, I'm off to buy some photographic mattes to do experiements with. 
This is all about having a horizontal dial face that is not too bright 
to view even in the summer midday sun - so I'll go quiet now and report 
back after the summer solstice.


Steve



On 2017-02-28 1:40 AM, John Lynes wrote:

Hi Steve,
I'm sorry I've confused you.

...
The take-home conclusion is that there is no single ideal reflectance 
for the plate of a sundial.  It varies with the sky illuminance.  When 
Weber's Law prevails, a reflectance of about 60 per cent is likely to 
be a safe bet.


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Re: Sun path polar chart generator

[Roger Bailey]

Hello Dan,

Helmut Sonderegger's Sonne software can generate such a chart. Choose the type 
as "horizontal altitude" and try various options. Sonne is available here.
http://www.helson.at/sun.htm

Regards, Roger Bailey


From: Dan-George Uza 
Sent: Monday, February 27, 2017 12:10 PM
To: Helmut Haase 
Cc: sundial@uni-koeln.de 
Subject: Re: Sun path polar chart generator


Something like this.



​



Dan Uza


On Mon, Feb 27, 2017 at 8:40 PM, Helmut Haase  
wrote:

  Hell Dan-George,
  Could you post an example graph how the plot should approximately look like?

  Regards
  Helmut Haase

  -- 
  Am 27.02.2017 15:49, schrieb Dan-George Uza:

Hello,


I'm looking for a freeware solution to generate customizable polar sun path 
charts in vector format. The software should be able to display sun paths for a 
custom time interval (like daily, weekly) and feature analemma curves for 
standard hours. Any help will be appreciated!


Dan Uza   

 

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Re: Dial face colouration

[John Lynes]

Hi Steve,
I'm sorry I've confused you.
The experiments reported in the 1941 UK paper were limited to illuminances
not exceeding 10 000 lux.  For that reason I had to admit that higher
illuminances might well point to a different conclusion.  I certainly did
not intend to suggest that reflected light should be limited to 6000 lumens
per square metre; simply that I have no experimental evidence handy for
illuminances exceeding 10 000 lux.

Weber's Law stated that if the background luminance is Lb and the stimulus
luminance is Ls, then the just-detectable luminance difference (Ls - Lb),
or in the case of a sundial (Lb - Ls), is proportional to Lb.  If Weber's
Law were correct then the perceived contrast of the shadow on a matt
sundial plate would be independent of the reflectance of the plate.

Although Weber's "Law" is approximately true, for many practical purposes,
over a wide range of values for Lb, it certainly fails under dim lighting
and under very bright lighting, when the "Weber fraction" (Lb - Ls)/Lb
rises.

Ideally for a sundial plate one would aim for the value of Lb which
minimises the Weber fraction.  Unfortunately there is little agreement over
the precise value of Lb at which this minimum occurs.  It is almost
certainly greater than 10 000 lumens per square meter of reflected light
but, as you have observed, well below the luminance of a white surface
under intense sunlight.

Once again I'm sorry to have confused you.  The take-home conclusion is
that there is no single ideal reflectance for the plate of a sundial.  It
varies with the sky illuminance.  When Weber's Law prevails, a reflectance
of about 60 per cent is likely to be a safe bet.

John Lynes
PS I'm away from my computer for the coming week, so will be out of touch
for some time.

On 28 February 2017 at 01:48, Steve Lelievre <
steve.lelievre.can...@gmail.com> wrote:

> John,
>
> Will you clarify some things for me?
>
> You mention that 50 lumens per square foot is about 500 lux, and that the
> cited article recommends a limit of 60% reflectance for sky illuminance of
> up to 1,000 lumens per sq. ft. If I multiple all that out, it would appear
> to suggest a a limit of 6,000 lux of reflected light for comfortable
> viewing. Is that the case?
>
> Through Google, I found empirical rules for calculating the wattage of
> solar radiation reaching the ground, depending on season, altitude,
> declination, hour angle, and geographic elevation. I also found a
> conversation factor for converting sky illumination in watts per square
> metre to lux. Putting it all together, I get a figure of about 72,000 -
> 91,000 lux for the incident illumination,  at noon on the northern
> hemisphere summer solstice at sea level, depending on latitude (and valid
> for mid-latitudes only). Using the mid figure of 80,000 lux, if I want to
> limit the reflected light to 6,000 lux then the reflectivity has to be less
> than 22.5%, which corresponds to a lightness of only 3.5 on the Munsell
> scale.
>
> Does this conversion make sense, or don't things work like that?
>
> Of course, if we've gone out in midday sun, we should be wearing
> sunglasses and, again from the web, sunglasses reduce the visible light
> reaching our eyes by two thirds or more. If I factor that in, my Munsell
> value rises to 5.3. And, as you pointed out, when the sun isn't so high in
> the sky, we can tolerate a more reflectivity on our dial face.
>
> Thanks for any further comments or advice,
>
> Steve
>
> P.S. Based on what I've learned so far, I'm leaning towards using a
> material with a Munsell value of 6 or 7, which would correspond to the
> mid-grays, tans and browns that people have been suggesting may work in
> practice. It would be the number you mentioned but with the lightness
> notched down a little. My design latitude of 45N is a little further south
> than England (where the article's authors came from) and the summer sun is
> a tad brighter. As well, I reckon a suitable colour with a number of 6 or 7
> would look OK against a lawn, flowerbed or other greenery.
>
>
>
> On 2017-02-26 7:08 AM, John Lynes wrote:
>
> There is no single optimum reflectance for a flat dial face.  Obviously
> under dim sunlight the optimum reflectance would be 100 per cent,
> i.e.perfect white.
> Under intense sunlight, contrast sensitivity would be optimised for a
> lower value of reflectance.  Thousands of papers have been written on
> contrast sensitivity.  One classical study is "Brightness and contrast in
> illuminating engineering" by RG Hopkinson, WR Stevens and JM Waldram,
> Transactions of the Illuminating Engineering Society (London), Vol 6, No 3,
> pp 37-48 (1941).  This indicates that when the sky illuminance on a matt
> dial face is over about 50 lumens per square foot (about 500 lux) the
> optimum reflectance would be about 60 per cent (a light grey, about Munsell
> Value 8).  Below this illuminance (which would correspond to a solar
> altitude close to sunrise or sunset) the optimum