Re: Worldmap mercator projection - Latitude to Y calculation. - last try

Paul,

>  ln(2.097283) = 0.740643   # Via the ln() button on my calculator

And that 0.740643 points to somewhere between the northpole and canada on an
ice plate.  Where I'm quite sure Washington DC isn't located.

Which was why I started to doubt that "ln()" equals "log()".  But if not,
what is it ?

> The plot origin must not be where we think it is.

Well, thats easy to check : Just calculate the result for a Latitude of Zero
degrees.  It should point at the equator.

> Notice how in a lot of these mathematics discussions, nobody labels a damn
> thing.

Just mathematics ?    A couple of weeks ago I tried to find example code for
OpenSLL.  I could find some, but with zero indication which version of the
DLL it was for - and it matters a *lot*.  It frustrates me to no end.

>> 0.117959 is *way* to low
>
> But it is 0.5 minus that number, so 0.382 .

In my previous message I mentioned that I multiply the result by half the
height of the map, and subtract it from the equator (again, half the height
of the map).  That is the same, right ?

Actually, it isn't.  :-)

Now you have shown that the log() in the formule you presented is exactly
that (and not a elog() (natural log?) ) I had some solid ground from which I
could look further.

The whole problem is that your formule multiplies by the full height of the
map, and my "simplified" one multiplied by *half* the maps height (and than
subtracts from the equator).

When I multiplied my result by two the result was the same as what came
outof your formule.

Thank you for that. :-)

mea culpa : after noticing that my implementation of the formule didn't work 
I *should* have first tried to implement it as provided. :-|


Than only one thing remains : Any idea why the first formule doesn't give
the expected result ?<whistle>

Regards,
Rudy Wieser