[Proj] Re: Global Gauss-Kruger and libproj4---the final story
Gerald I. Evenden
geraldi.evenden at gmail.com
Thu Aug 28 11:46:59 EDT 2008
On Thursday 28 August 2008 12:37:36 am strebe wrote:
> On Aug 27, 2008, at 5:32:33 PM, "Gerald I. Evenden"
> <geraldi.evenden at gmail.com> wrote:
> Yes, you run into them every 10 to 20 years.
> No, I run into them commonly. Perhaps you run into them every ten or twenty
Perhaps you would like to present an example.
> No other projection has a requirement that the user needs to know an
> arcane formula to manipulate graphical usage to interpret the results.
> There is currently no means for libproj4 to return such information.
> I do not understand that utterance. The problem has nothing to with
> "graphical usage", whatever that means. It has to do with the results of
> the projection at a single point. Many world projections do not come with a
> 90°N/S, 180° E/W natural boundary that the client software can treat as
> some fixed convention, and all projections have interruptions. An
> interruption automatically means the projection formulæ are not a function,
> which renders this utterance invalid:
The only context that I use the term "interruption" in discussing cartographic
projections are in cases like Goode's world maps or "orange peal" charts
often using the sinusoidal projection. Please define what *you* mean by
> I am tired of repeating, libproj4 is *NOT* a graphic routine any more than
> sine or tangent. In the case of making maps it is merely the process that
> transforms information from one coordinate system to another!
> Sine and tangent are functions. A projection is not.
Let us stop here for a moment. From an online dictionary: "function (math) A
quantity so connected with another quantity that if any alteration be made in
the latter there will be a consequential alteration in the former." In this
case lat,lon <=>x,y. Change lat,lon and you change x,y and vice versa. The
mechanism that determines the functional relationship is the cartographic
transformation---a procedure that defines the relationship between two
coordinate systems. In the case of computing Z=f(K), f is a function.
> It is generating
> formulæ that are (usually) a function over the range of the map except at
> boundaries, where they are multivalued. You have chosen, for your own
> convenience, to ignore the the possible multiple results of the projecting
> formulæ. That is fine, but it does not make your rant correct; it only
> makes your decision convenient for you. In any case, if you're tired of
> repeating yourself, then quit repeating yourself. I suspect everyone else
> is tired of it, too — particularly because it's a straw man.
> Would you like a list of world projections whose boundaries differ from the
> boundaries of finite cylindric projections?
I am aware of some, especially those I call cartoon projections (I do not mean
that in a pejorative way) like those that plot the world on a cube or some
other solid or ones with very odd boundary system. These are usually very
interrupted projections requiring difficult geographic clipping functions
that (other than longitude range reduction) is *not* a function of libproj4.
We have already covered the +-180 problem and flat pole maps. Let's see,
cylindricals, pseudocylindricals, conics, globulars, ... . Even general
oblique projections are no problem other than odd boundaries. I managed to
make plots of the above with libproj4 as it now stands. See manual.
Please list a few provided there is a url to a picture of the listed
> And if there are many
> projections with other kinds of boundaries, would you explain again how it
> is that the ellipsoidal transverse Mercator is somehow unique in that
> I don't care if you don't implement a global ellipsoidal transverse
> Mercator. If you don't want to implement it, then don't implement it.
> Surely no one can begrudge that — no one's paying you to, as far as I know.
> I just don't see the point of rationalizing that decision with sophistry,
> or why you'd expect your audience to swallow the rationalizations. I
> suggest just stating that you're not convinced of the value of the work, or
> that you hate the ellipsoidal transverse Mercator, or that you're tired,
> and be done with it. Which reminds me: once again, I am tired of these
> sorts of conversations, and am done with this one.
Oh gee. But this is so much fun! Please don't go.
> -- daan Strebe
The whole religious complexion of the modern world is due
to the absence from Jerusalem of a lunatic asylum.
-- Havelock Ellis (1859-1939) British psychologist
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