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<font face="Calibri">Thanks for taking the time to check it out. I
see it mostly as a preservation work, not as a starting point.
That is why my JS "implementation" adheres as much as possible to
Synder's original formulas, without any clever tricks or
optimizations. The library of Congress preserves <a
href="https://blogs.loc.gov/maps/2015/11/saving-early-computer-cartography/">Snyder's
TI-59 calculator</a> and magnetic strips.<br>
<br>
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<pre class="moz-signature" cols="72">Mircea Neacsu
M: 514-591-0329
E: <a class="moz-txt-link-abbreviated" href="mailto:mircea@neacsu.net">mircea@neacsu.net</a></pre>
<div class="moz-cite-prefix">On 4/5/2024 10:33 AM, Charles Karney
wrote:<br>
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<blockquote type="cite"
cite="mid:CAH36mb9bmysEo8We=noeyFieCOBuVCKsbP0dcA0r6p6wgo4qQg@mail.gmail.com">
<pre class="moz-quote-pre" wrap="">I have mixed feelings about your enterprise. Undoubtedly, Snyder (1987)
is an invaluable resource and it was the foundation for Gerald Evenden's
implementation of PROJ. However, time marches on, and, while it remains
a useful reference work, it's probably not the best place to start when
implementing new code. A few examples:
* most of the series used by Snyder are in the eccentricity, e. In
nearly every case the corresponding series in the third eccentricity,
n, converges faster. In particular, this is the case for all the
conversions between auxiliary latitudes.
* many of his expressions for conformal projection express the integral
of sec(phi) as log(tan(pi/4 + phi/2)). For computational purposes,
asinh(tan(phi)) is preferred (more accuracy near the equator and poles
and transparently odd).
* he uses a terrible series for the transverse Mercator projection.
--Charles
On Sat, Mar 30, 2024 at 7:01 PM Mircea Neacsu via PROJ
<a class="moz-txt-link-rfc2396E" href="mailto:proj@lists.osgeo.org"><proj@lists.osgeo.org></a> wrote:
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Hello,
My work of converting Snyder – Map Projection Manual to HTML is almost finished. Probably the most interesting part are the numerical examples, implemented using JavaScript. All formulas can be recalculated, and one can see all the intermediate steps and the result of those calculations.
I would very much like to hear your comments. Given the number of formulas, I’m sure there are many errors that have slipped through, and I will be grateful if you will point those out.
Thank you,
--
Mircea Neacsu
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