From octave-sources-request at bevo dot che dot wisc dot edu Mon Jan 27 14:10:47 2003
Subject: area2metric.m
From: Stefan Burger <s dot burger at debitel dot net>
To: octave-sources at bevo dot che dot wisc dot edu
Date: Mon, 27 Jan 2003 07:44:36 -0600


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## Copyright (C) 2003 Stefan Burger
##
## This file is part of Octave.
##
## Octave is free software; you can redistribute it and/or modify it
## under the terms of the GNU General Public License as published by the
## Free Software Foundation; either version 2, or (at your option) any
## later version.
##
## Octave is distributed in the hope that it will be useful, but WITHOUT
## ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
## FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
## for more details.
##
## You should have received a copy of the GNU General Public License
## along with Octave; see the file COPYING.  If not, write to the Free
## Software Foundation, 59 Temple Place, Suite 330, Boston, MA 02111 USA.

## -*- texinfo -*-
##  at deftypefn {Function File} {} area2metric (@var{unitstr}, @var{val}, @var{metstr}, )
## Converts metric measures to non-SI or US area measures  .
## Input:
##  at var{val} 	; Value to be converted,
##  at var{unitstr}	: unit to be converted to,
##  at var{metstr} 	: unit to be converted from, optional, defaults to 'm', meters.
##
## Currently, the following units are supported:
## in2, squareinch, ft2, squarefoot, USsurvey-squarefoot, yd2, squareyard, mi2, squaremile,
## USsurvey-squaremile, acre
##
## Metric units:
## km2, m2, dm2, cm2, mm2, um2, nm2.
##
## References:
## See NIST Guide to SI units, Appendix B8,
## at www.nist.gov/Pubs/SP811/appenB8.html
##
##  at end deftypefn
##  at seealso{metric2area, len2metric and vol2metric}

## Author: Stefan Burger <Stefan dot Burger at stud dot tu-muenchen dot de>
## Description: converts area values to SI (metric) area units.

function v = area2metric (unitstr, val, metstr)

  if (nargin ==1)
   val = 1.0;
   metstr = "m2";
   %% if no value given, default to one.
   %% if no metric string given, default to meters.
   %% reason: usage val * len2metric("inch")
  endif

  if (nargin == 2)
   metstr = "m2";
   %% if not specified, default to meters
  elseif (nargin < 1 || nargin > 3 )
    usage("area2metric(unitstr [, val, metstr])");
  endif

  if (! (isstr(unitstr) && isstr(metstr)))
    usage("area2metric(unitstr [, val, metstr])");
  endif

  switch (unitstr)
    %% determine conversion value from input unit
    %% to standard meters squared
    case {"in2", "square-inch"}
      fv = ( len2metric("inch") )^2;
    case {"ft2", "square-foot"}
      fv = ( len2metric("foot") )^2;
    case {"USsurvey-squarefoot"}
      fv = ( len2metric("USsurvey-foot") )^2;
    case {"mi2", "square-mile"}
      fv = ( len2metric("mile") )^2;
    case {"USsurvey-squaremile"}
      fv = ( len2metric("USsurvey-mile") )^2;
    case {"acre"}
      fv = 160 * ( len2metric("rod") )^2;
      %%  or, alternatively,
      %%  fv = 43560* (len2metric("USsurvey-foot", 1, m) )^2;
      %% 1 acre = 160 rod squared = 160 * 272.25 USsurveyfoot ^2
    case {"circular-mil"}
      fv = ( len2metric("inch") / 2000 ) ^ 2 *pi;
      %% area of circle with diameter 1 mil
      %% thus, 1 mil = inch/1000,
      %% radius = diameter / 2,
      %% area = radius ^ 2 * PI.
    case {"squareyard"; "yd2"}
      fv = len2metric("yard",1,"m")^2;
    case {"section"}
      fv = (len2metric("USsurvey-mile")) ^2;
      %% basically another name for US-survey-square-mile.
    case {"township"}
     fv = 36 * (len2metric("USsurvey-mile")) ^2;
     %% 1 township equals 36 sections.
    case {"homestead"}
      fv = 160 * (160 * ( len2metric("rod") )^2);
      %% 1 homestead equals 160 acre.
      %% Area of land granted by the 1862 Homestead Act of the United States Congress
      %%
      %% The following units are not-so-common units based on the metric system.
    case {"are"}
      fv = 1E2;
      %% 1 are equals 100 square meters
    case {"hectare"}
      fv = 1E4;
      %% 1 hectare equals 100 are, equals 1/100 kilometer squared.
      %%
      %% also allow for metric units to be converted from.
    case {"m2"}      %% meter squared
      fv = 1;
    case {"km2"}     %% kilometer squared
      fv = 1E6;
    case {"dm2"}     %% decimeter squared
      fv = 01E-2;
    case {"cm2"}     %% centimeter squared
      fv = 1E-4;
    case {"mm2"}    %% millimeter squared
      fv = 1E-6;
    case {"um2"}    %% micrometer squared
      fv = 1E-12;
    case {"nm2"}    %% nanometer squared
      fv = 1E-18;
    otherwise
      disp (unitstr)
      error ("area2metric: unrecognized option");
  endswitch

  switch (metstr)
    %% determine conversion value from standard meters squared
    %% to unit desired.
    case {"m2"}      %% meter squared
      fm = 1;
    case {"km2"}     %% kilometer squared
      fm = 1E-6;
    case {"dm2"}     %% decimeter squared
      fm = 1E2;
    case {"cm2"}     %% centimeter squared
      fm = 1E4;
    case {"mm2"}    %% millimeter squared
      fm = 1E6;
    case {"um2"}    %% micrometer squared
      fm = 1E12;
    case {"nm2"}    %% nanometer squared
      fm = 1E18;
    otherwise
      disp (metstr)
      error("area2metric: unrecognized option");
  endswitch

  v = val * fv * fm;

endfunction

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