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RE: Re: Map Projection with Mathematica

  • To: mathgroup at smc.vnet.net
  • Subject: [mg40330] RE: [mg40293] Re: Map Projection with Mathematica
  • From: "Wolf, Hartmut" <Hartmut.Wolf at t-systems.com>
  • Date: Wed, 2 Apr 2003 04:33:50 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

Thiery,

as I understand you, you are going to experiment and to learn. Studying
WorldPlot is a good way to do so, but stay critical.  I have had a look into
it, once, to do some fixes, but then came to the conclusion not to spent the
time.

To my opinion the data structure describing geographical objects,
"countries", is a bit too weak, say: although it allows to describe New
Zealand, with its isles, it would not allow for the EC with Switzerland as a
whole in it, or Russia with the Baikal Sea. It is not consistent treating
orientation (which would allow to cut out the Baikal Sea e.g.). Boundaries
between countries should also be described by a single instance, etc.

Of course there is much to be learnt from it, but compare to a modern text
on GIS (geographica data systems) for the data structures, and an any (old
or not so old) text on geodesy (for the mathematics). Knowledges on
geometrical algorithms, e.g. polygon triangulation, clipping, is helpful.

The Mathematica database should be fixed up a bit (write a program to do
that!): identify points closer than ... (find out), close open lines, orient
the countries. Think about 180 degrees west/east.

For the algorithms, have a look at them. You'll see the thoughts, decisions,
and problems of the author, perhaps you can find out alternatives.  Fix up
the clipping algorithm!

--
Hartmut


>-----Original Message-----
>From: Bill Rowe [mailto:listuser at earthlink.net]
To: mathgroup at smc.vnet.net
>Sent: Sunday, March 30, 2003 11:09 AM
>To: mathgroup at smc.vnet.net
>Subject: [mg40330] [mg40293] Re: Map Projection with Mathematica
>
>
>On 3/29/03 at 5:20 AM, thiery.balser at gmx.net (Thiery Balser) wrote:
>
>>I'm wondering whether there's a smart way to do map projections with
>>mathematica.
>
>>I know that mathematica comes along with the package `WorldPlot. So is
>>there anyway to access the data they're using there? They even got
>>some different projections options but the point is that I want to do
>>in on my own.
>
>>Has anyone got experience in this?
>
>Have you opened the file WorldPlot.m that comes with 
>Mathematica using a text editor or something else that can 
>display ASCII? If you do this you will find you can review the 
>code used to implement each of the functions. Additionally, 
>there is information regarding the sources used to develop 
>this package.
>
>As far as accessing the data used, the first line of code 
>after the comments is
>
>BeginPackage["Miscellaneous`WorldPlot`","Miscellaneous`WorldNames`",
>        "Miscellaneous`WorldData`","Utilities`FilterOptions`"]
>
>suggesting the file WorldData.m contains the data of interest. 
>And that file contains the comment
>
>(* :Source:
>    These data are derived from what was originally a CIA database,
>    released into the public domain by the Freedom of Information
>    Act.  I acquired a copy of these data, and rearranged them
>    to the form below.  The copy I found was from the Amiga
>    Fish disks, a public-domain distribution of software for the
>    Amiga computer, under the name WorldDataBank.  Note that these
>    data (in the original format) are available at higher resolution
>    from this source.
>*)
>
>Looking at the packages that were distributed with Mathematica 
>is a very good way to learn by example many useful techniques.
>




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