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2004 May 04 17:59

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Re: [vox-tech] Has anyone done cartography on Linux?
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Re: [vox-tech] Has anyone done cartography on Linux?



hi henry,

sounds like a 4-6 hour SDL programming project (2-3 hours for bill).

collect a bunch of mouse clicks, and it's not too difficult to calculate
a perimeter using the coordinates, assuming you only have piecewise
straight lines and a scaling.  just the good old pythagorean theorem
(except for the degenerate vertical line case).

i took graduate differential geometry with dr. thurston at UCD.  one of
the things i learned (he was surprised that nobody in the class knew
this, but i don't know where we'd see it) was that you can calculate the
area of an arbitrary n sided polygon (an n-gon) using a rank n
determinant.

i forget the exact details, but it shouldn't be too hard to find.

what else would you need?

there's nothing out there that does this?

pete


On Tue 04 May 04,  1:49 PM, Henry House <hajhouse@houseag.com> said:
> Has anyone here worked with maps on Linux? I periodically need to work with
> simple maps and I am continually frustrated with the tools that I have
> tried. Here is an example of something that I want to do:
> 
> 1. Scan an aerial photo or existing map
> 2. Mark some key points on it, connect them with lines or curves, make
>    areas, etc. These might be fields or fences.
> 3. Calculate lengths and areas (for example, number of acres in a field or
>    number of miles long that a fence extends).
> 
> I don't have databases of geospacial data or GPS receiver data, so I don't
> think a heavyweight GIS system what I want. The scales are normally small so
> map projections are not a major issue. Anyway, what I want to do is so
> simple that I don't think it is worth learning a complex system like GRASS
> (<http://packages.debian.org/testing/science/grass>) since I can do a crude
> job with pencil, ruler, and compensating polar planimiter* in not much time.
> Still, there is surely a better way. I am interested in any suggestions.
> 
> * A mechanical device that, when adjusted for scale, calculates the area of
>   any shape that one traces on a map or photograph.
> 
> -- 
> Henry House
> The unintelligible text that may follow is a digital signature.
> See <http://hajhouse.org/pgp> to find out how to verify it.
> My OpenPGP key: <http://hajhouse.org/hajhouse.asc>.
> 



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