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Hi Bob,
That's a wonderful idea! A Delta Cad
Macro of the EOT correction with an option for including the longitude
correction. That way, one could get a graph or a table in a DC drawing
format. I think it would be a very useful tool for many dialists, not just
myself. So far, several people have sent me Excell spreadsheets or
websites that will do the calculations and present them in tabular form, but
none of them produce a graph.
If I had my druthers, I'd want the graph to be of
an average year (not a leap year), and for an average time of day (12
noon). It would be very helpful, from a design point of view, if the DC
macro also had options for making the graph stretched out
(elongated) or compressed horizontally because sometimes, when
designing a sundial face there is not a lot of extra room for the graph, so it
would be nice if it could create graphs of different
shapes.
If you can't include the stretching option, I
suppose one could export a PDF of your DC macro drawing to Photoshop and use its
stretch tool.
Great idea Bob, if you ever do this, be sure to let
everybody know about it!
Have fun
p.s. Hope you don't mind me ccing this letter
to the Sundial List.
----- Original Message -----
Sent: Thursday, July 08, 2004 10:09
AM
Subject: Re: EOT + Longitude Correction
Table
John, I understand what you are saying about a graph that combines both eot
and long-correction for dials that do not have long-correction built in. In
the past I have written PostScript applications that would do just exactly
that. As I recall, I started to convert that process into a DeltaCad
Macro a couple of years ago. It should be easy to do. Let me know if you want
me to pursue that while I am kindof inactive up here in Idaho this summer.
Bob Hough - ShadowMaster
--------------
Original message --------------
> Hello All,
>
>
Some of you wrote me and seemed very confused with my inquiry about a way to
> get a EOT table that is longitude corrected. You ot understand what
I
> wanted. So I'll try to explain it here. (thanks to everybody who
sent me
> info on this)
>
> Sample letter:
> "I
still cannot figure out your EoT problem; EoT does not depend on
>
longitude, it depends on an agreed absolute (GMT) and changes so little in
> any time zone you cannot see the difference on a dial. Maybe I am
missing
> something, I often do these days."
>
> Yes,
you are missing something. And it's so simple you will kick yourself.
> You're thinking too deeply! I'll try to explain...
>
> Of course you are correct in implying that EOT values are
"Universal" and
> are basically the same all over the world, at any
longitude or latitude and
> on any given date. You can use the same
EOT graph with almost any sundial
> anywhere in the world. But you
know that already. So far so good.
>
> But if somebody really
wants to know "clock" time, then not only does he
> have to correct
his sundial readings for EOT, but he also has to correct for
> his
longitude (and Daylight Saving Time if applicable). This additional
>
longitude correction is expressed as a plus or minus value in minutes and
> seconds. But you know this already. So far so good.
>
> Now this double correction is sometimes confusing to non-dialists
(it's a
> triple correction if one has to correct for Daylight
Savings too). So to
> reduce two time reading corrections into just
one correction, you can add
> the EOT correction to the longitude
correction since both expressed in
> minutes and seconds, and you
come up with a new EOT graph or table that
> incorporates the
longitude time correction in its values.
>
> Now do you get
it? Neat huh!
>
> For my sundial customers, I usually build
the longitude correction directly
> into my sundial faces so the
customer doesn't have to do the longitude
> correction, just the EOT
correction. This combined EOT+Longitude Correction
> Table is very
useful if you have an antique pre-timezone sundial or any
> sundial
that doesn't have a built-in longitude correction. The downside is
>
that you have to make a unique customized EOT table for each sundial,
> depending on its particular longitude.
>
> Hope this
helps
>
>
>
>
> -
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