gtoc is a simple library that converts a geographic coordinate to a Cartesian coordinate in Ruby.

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Overview

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This library converts a geographic coordinate that consists of a north latitude and an east longitude, to a Cartesian coordinate that consists of a reference geographic coordinate, an x coordinate and a y coordinate. The unit of latitude and longitude is decimal degree. The unit of x and y is meter. Unfortunately this library currently supports Japanese coordinate only. Most of the equations are referred from this web page.

QuickStart

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This software works on Ruby. After installing Ruby, a sample in bin directory works simply as follows:

ruby bin/gtoc *args

You can check the arguments of the application. For example, you want to get the x-y coordinates of 33.0 north latitude and 129.5 east longitude, executes the application as follows:

ruby bin/gtoc -e 33.0 -n 129.5 -m 1

-m option specifies the reference geographic coordinate. If you want to know the details, please check this web page. (The web page is in Japanese, but you can set your reference geographic coordinate as library use.) You can get an x-y coordinate in world geodetic datum if -t option is specified.

ruby bin/gtoc -e 33.0 -n 129.5 -m 1 -t "world"

The default value of -t option is "japan".

How to Use

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An easiest way to know how to use the library, is to check bin/gtoc.

require 'gtoc'
include Geographic

gtoc(latitude: 33.0, longitude: 129.5, number: 1, type: "world")
=> {x:=>0.0, y:=>0.0, m:=>0.9999}

gtoc returns a hash including a x coordinate, a y coordinate and a point scale factor. As explained above, latitude is a north latitude, longitude is an east longitude, number is a reference geographic coordinate number and type is a type of geodetic datum. If you want to specify your own reference geographic coordinate,

gtoc(latitude: 33.0, longitude: 129.5, default_latitude: 32.9, default_longitude: 129.4)
=> {x:=>11093.689031, y:=>9344.3898872, m=>0.9999011}

If the inputted arguments are invalid or the point scale factor is too large, gtoc returns nil and the point scale factor.

gtoc(latitude: 33.0, longitude: 129.5, number: 0)
=> {x:=>nil, y:=>nil, m=>nil}

gtoc(latitude: 33.0, longitude: 139.5, default_latitude: 32.9, default_longitude: 129.4)
=> {x:=>nil, y:=>nil, m=>1.0194529}

Document

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Rdoc document can be generated as follows:

rake rdoc

Test

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Unit test can be done as follows:

rake test

Reference

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Equations used in codes: http://vldb.gsi.go.jp/sokuchi/surveycalc/algorithm/

Reference geographic coordinates: http://vldb.gsi.go.jp/sokuchi/patchjgd/download/Help/jpc/jpc.htm