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

On 2026/1/19 20:11:34, R.Wieser wrote:
> As I cannot get any formule to work I'm going to try this one last time.

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There are three stages to this - I would say best sorted individually
before trying to combine them. (Stages 2 and 3 are related and might
need reversing in order.)

1. The mathematical conversion from latitude (and longitude) to the
position on the plane map *relative to its centre*, assuming that's
where the Greenwich meridian crosses the equator. This is the one that
might or might not be just a tangent function (for latitude; for
longitude, it's just scaling and offset, see below).

2. The _scaling_ required, depending on the size of the map image. Which
again will depend on the size of the image (and may be different for X
and Y).

3. The _offsetting_ required to account for the fact that the above
point is not at 0, 0 on the image (probably offset by half the size of
the map being used, in pixels, in each direction).

I think _most_ of those contributing to this discussion know that, but
have not been making it very clear which bits of their formula(e) do what.
-- 
J. P. Gilliver. UMRA: 1960/<1985 MB++G()ALIS-Ch++(p)Ar++T+H+Sh0!:`)DNAf

The fact that there is a highway to hell and only a stairway to heaven
says a lot about anticipated traffic numbers.