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

On Sat, 1/24/2026 3:42 AM, R.Wieser wrote:
> Paul,
> 
>> I wrote a program, worked an example and put a dot on a map
>> in a posted picture. That's enough.
> 
> I already knew that both of those formules where expected to work, so you 
> wasted your time in proving that your CoPilot provided one does.
> 
> *What I was asking for* was a bit of help to why my implementation of first 
> one, than both formules refused to return a usable result.   I gave you 
> *everything* to be able to do so.
> 
> You think that what you did was enough ?   How ?  You did not even *try* to 
> answer my question. :-(
> 
> Regards,
> Rudy Wieser
> 
> 

Show me current code.

Have the program print out something like this.

Enter Latitude in degrees: -80    Y=0.887741
Enter Latitude in degrees: -50    Y=0.660855
Enter Latitude in degrees: -30    Y=0.587425
Enter Latitude in degrees:   0    Y=0.500000
Enter Latitude in degrees:  30    Y=0.412575 \___ 39 degrees is between these two
Enter Latitude in degrees:  50    Y=0.339145 /
Enter Latitude in degrees:  80    Y=0.112259

You can see from the output, I'm covering most of a unit square
and my output graph origin must be in one of the
corners of the unit square.

We know the equation is not valid past 85 degrees
at either end, so that range of values will
tell us whether we are covering a unit square or not.

Most of the trouble with this stuff, seems to be
with origin-of-map and origin-of-unit-square.

If we enter (0,0) for lat-long we expect to be in the middle
of the unit square. You can see my Y above is 0.5 in that case.

You can check in Wikipedia for the icon next to the
lat-long for a city, and that icon (with a good browser)
will yield a pop-up map with enough detail you can
fit it to your map data.

   Paul