[Proj] Extended range TM usage

support.mn at elisanet.fi support.mn at elisanet.fi
Tue Aug 26 08:35:43 EDT 2008

"Gerald I. Evenden" <geraldi.evenden at gmail.com> wrote: 

> My question is can anyone supply a rational reason for the practical use of an
> elliptical TM projection with extended longitude range.

How practical is that, I don't know, but there is the situation where an user
is zooming out a view so much that a very large area is visible. There can rise
a situation where those extreme areas should be shown somehow. The
accuracy does not matter in that case, since it is only show in relation with
that middle section which is the main focus.

This same situation applies basicly to all projections. Sometimes users zoom
out the views very much and the extreme areas should be shown somehow.
Sometimes clipping them away, or projecting to some limiting line, might be
as good alternative. But my opinion is that it is better to show something than
nothing even if it is a bit unaccurate.

If somebody wants to have more aggressive limiting, he might use the error
mechanism, where the library warns him about the error getting too large
and that particular solution might start to clip those areas away.

Regards: Janne

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