Hi Hans, Aditya, and all,
Me:
>>>> I’d like to use the mp-geo Metapost package with ConTeXt to draw simple
>>> globes viewed from various directions. The package is here:
>>>>
>>>> https://melusine.eu.org/syracuse/poulecl/mp-geo/
>>>> <https://melusine.eu.org/syracuse/poulecl/mp-geo/>
Aditya:
>> Actually the data files are fairly simple:
>> no_of_points
>> <list of coordinates>
>> So, it would be much simpler to read and parse it via lua rather than
>> scantokens. Rest of the code simply determines a "view" of what to show. So,
>> it can be a good exercise in lua-MP interface.
Hans:
> I was wondering about that too. I admit that I looked into maps years ago but
> never could find quality data files.
This is great fun! I slightly altered Hans’ code to produce the most basic area
preserving projection of North America (code and map below). If anyone else is
playing with the mp-geo data, it is in arc minutes, so divide by 60 to get
degrees.
For my book I only want 5cm diameter globes with continents, so the map data in
the mp-geo package is far more detailed than I need. The code is so fast, the
detail doesn’t seem to be a problem.
I just started learning Metapost a month ago, and it’s great. I know almost
nothing about Lua, but this looks like a fun project for learning more!
Thanks!
Gavin
P.S. I marked the location of our local ConTeXt users group on the map, in case
any of you want to visit.
\starttext
\startluacode
function mp.maptopath(filename)
local t = { cycle = true }
for phi, theta in
string.gmatch(io.loaddata(filename),"%(([%+%-%d]+),([%+%-%d]+)%)") do
t[#t+1] = { math.cosd(tonumber(phi)/60)*tonumber(theta+6125)/12,
tonumber(phi)/12 }
end
mp.inject.path(t)
end
\stopluacode
\startMPpage
fill lua.mp.maptopath("data/usa1.dat");
fill lua.mp.maptopath("data/usa2.dat") ;
fill lua.mp.maptopath("data/mexique.dat") ;
fill lua.mp.maptopath("data/canada.dat") ;
fill fullcircle scaled 5 shifted (0, 203) withcolor white;
\stopMPpage
\stoptext
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