This image can be completely generated by the following source code. If you have the gnu compiler collection installed, the programm can be compiled by the following commands:
It creates file Sphere_wireframe.svg in working directory. This file can be viewed using rsvg-view program :
/* sphere - creates a svg vector-graphics file which depicts a wireframe sphere
*
* Copyright (C) 2008 Wikimedia foundation
*
* This program 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.
*
* This program 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 this program; if not, you can either send email to this
* program's author (see below) or write to:
* The Free Software Foundation, Inc.
* 51 Franklin Street, Fifth Floor
* Boston, MA 02110-1301 USA
*/
/* The expressions in this code are not proven to be correct.
* Hence this code probably contains lots of bugs. Be aware! */
#include<iostream>
#include<cmath>
#include<cstdlib>
#include<cstring>
usingnamespacestd;
constdoublePI=3.1415926535897932;
constdoubleDEG=PI/180.0;
/********************************* settings **********************************/
intn_lon=18;// number of latitude fields (18 => 10° each)
intn_lat=18;// half number of longitude fields (18 => 10° each)
doublelon_offset=2.5*DEG;// offset of the meridians
doublew=52.5*DEG;// axial tilt (0° => axis is perpendicular to image plane)
doublestripe_grad=0.5*DEG;// width of each line
intimage_size=400;// width and height of the image in pixels
doubleback_opacity=0.25;// opacity of the sphere's backside
charcolor[]="#334070";// color of lines
intistep=2;// svg code indentation step
/*****************************************************************************/
doublesqr(doublex)
{
return(x*x);
}
// commands for svg-code:
voidindent(intn,boolin_tag=false)
{
n*=istep;
if(in_tag)n+=istep+1;
for(inti=0;i<n;i++)cout<<" ";
}
voidM()
{
cout<<"M ";
}
voidZ()
{
cout<<"Z ";
}
voidxy(doublex,doubley)
{
cout<<x<<",";
cout<<y<<" ";
}
voidarc(doublea,doubleb,doublex_axis_rot,boollarge_arc,boolsweep)
{// draws an elliptic arc
if(b<0.5E-6)
{// flat ellipses are not rendered properly => use line
cout<<"L ";
}
else
{
cout<<"A ";
cout<<a<<",";// semi-major axis
cout<<b<<" ";// semi-minor axis
cout<<x_axis_rot<<" ";
cout<<large_arc<<" ";
cout<<sweep<<" ";
}
}
voidcircle(boolclockwise)
{
M();
xy(-1,0);
arc(1,1,0,0,!clockwise);
xy(1,0);
arc(1,1,0,0,!clockwise);
xy(-1,0);
Z();
}
voidstart_svg_file()
{
cout<<"<?xml version=\"1.0\" encoding=\"UTF-8\" standalone=\"no\"?>\n";
cout<<"<svg id=\"Sphere_wireframe\"\n";
cout<<" version=\"1.1\"\n";
cout<<" baseProfile=\"full\"\n";
cout<<" xmlns=\"http://www.w3.org/2000/svg\"\n";
cout<<" xmlns:xlink=\"http://www.w3.org/1999/xlink\"\n";
cout<<" width=\""<<image_size<<"\"\n";
cout<<" height=\""<<image_size<<"\">\n\n";
cout<<" <title>Sphere wireframe</title>\n\n";
cout<<" <desc>\n";
cout<<" about: http://commons.wikimedia.org/wiki/Image:Sphere_wireframe.svg\n";
cout<<" rights: GNU Free Documentation license,\n";
cout<<" Creative Commons Attribution ShareAlike license\n";
cout<<" </desc>\n\n";
cout<<" <g id=\"sphere\" transform=\"scale("<<0.5*image_size;
cout<<", "<<-0.5*image_size<<") translate(1, -1)\">\n";
}
voidend_svg_file()
{
cout<<" </g>\n</svg>\n";
}
intmain(intargc,char*argv[])
{
// accept -lat and -lon as parameter
for(inti=2;i<argc;i++)
{
if(isdigit(argv[i][0])||(sizeof(argv[i])>sizeof(char)
&&isdigit(argv[i][1])
&&(argv[i][0]=='.'||argv[i][0]=='-')))
{
if(strcmp(argv[i-1],"-lon")==0)
{
lon_offset=atof(argv[i])*DEG;
}
if(strcmp(argv[i-1],"-lat")==0)
{
w=atof(argv[i])*DEG;
}
}
}
doublecosw=cos(w),sinw=sin(w);
doubled=0.5*stripe_grad;
start_svg_file();
intind=2;// initial indentation level
indent(ind);
cout<<"<g id=\"sphere_back\" transform=\"rotate(180)\" ";
cout<<"opacity=\""<<back_opacity<<"\">\n";
indent(++ind);
cout<<"<g id=\"sphere_half\">\n";
// meridians
indent(++ind);cout<<"<g id=\"meridians\"\n";
indent(ind++,true);
cout<<"style=\"stroke:none; fill:"<<color<<"; fill_rule:evenodd\">\n";
doublea=abs(cos(d));
for(inti_lon=0;i_lon<n_lat;i_lon++)
{// draw one meridian
doublelongitude=lon_offset+(i_lon*180.0/n_lat)*DEG;
doublelon[2];
lon[0]=longitude+d;
lon[1]=longitude-d;
indent(ind);
cout<<"<path id=\"meridian";
cout<<i_lon<<"\"\n";
indent(ind,true);
cout<<"d=\"";
doubleaxis_rot=atan2(-1.0/tan(longitude),cosw);
if(sinw<0)
axis_rot+=PI;
doublew2=sin(longitude)*sinw;
doubleb=abs(w2*cos(d));
doublesinw1=sin(d)/sqrt(1.0-sqr(sin(longitude)*sinw));
if(abs(sinw1)>=1.0)
{// stripe covers edge of the circle
doublew3=sqrt(1.0-sqr(w2))*sin(d);
circle(false);
// ellipse
M();
xy(sin(axis_rot)*w3-cos(axis_rot)*a,
-cos(axis_rot)*w3-sin(axis_rot)*a);
arc(a,b,axis_rot/DEG,0,0);
xy(sin(axis_rot)*w3+cos(axis_rot)*a,
-cos(axis_rot)*w3+sin(axis_rot)*a);
arc(a,b,axis_rot/DEG,0,0);
xy(sin(axis_rot)*w3-cos(axis_rot)*a,
-cos(axis_rot)*w3-sin(axis_rot)*a);
Z();
}
else
{// draw a disrupted ellipse bow
doublew1=asin(sinw1);
M();
xy(-cos(axis_rot+w1),-sin(axis_rot+w1));
arc(a,b,axis_rot/DEG,1,0);
xy(cos(axis_rot-w1),sin(axis_rot-w1));
arc(1,1,0,0,1);
xy(cos(axis_rot+w1),sin(axis_rot+w1));
arc(a,b,axis_rot/DEG,0,1);
xy(-cos(axis_rot-w1),-sin(axis_rot-w1));
arc(1,1,0,0,1);
xy(-cos(axis_rot+w1),-sin(axis_rot+w1));
}
Z();
cout<<"\" />\n";
}
indent(--ind);cout<<"</g>\n";
cout<<endl;
// circles of latitude
indent(ind);cout<<"<g id=\"circles_of_latitude\"\n";
indent(ind,true);
cout<<"style=\"stroke:none; fill:"<<color<<"; fill_rule:evenodd\">\n";
ind++;
for(inti_lat=1;i_lat<n_lon;i_lat++)
{// draw one circle of latitude
doublelatitude=(i_lat*180.0/n_lon-90.0)*DEG;
doublelat[2];
lat[0]=latitude+d;
lat[1]=latitude-d;
doublex[2],yd[2],ym[2];
for(inti=0;i<2;i++)
{
x[i]=abs(cos(lat[i]));
yd[i]=abs(cosw*cos(lat[i]));
ym[i]=sinw*sin(lat[i]);
}
doubleh[4];// height of each point above image plane
h[0]=sin(lat[0]+w);
h[1]=sin(lat[0]-w);
h[2]=sin(lat[1]+w);
h[3]=sin(lat[1]-w);
if(h[0]>0||h[1]>0||h[2]>0||h[3]>0)
{// at least any part visible
indent(ind);
cout<<"<path id=\"circle_of_latitude";
cout<<i_lat<<"\"\n";
indent(ind,true);
cout<<"d=\"";
for(inti=0;i<2;i++)
{
if((h[2*i]>=0&&h[2*i+1]>=0)
&&(h[2*i]>0||h[2*i+1]>0))
{// complete ellipse
M();
xy(-x[i],ym[i]);// startpoint
for(intz=1;z>-2;z-=2)
{
arc(x[i],yd[i],0,1,i);
xy(z*x[i],ym[i]);
}
Z();
if(h[2-2*i]*h[3-2*i]<0)
{// partly ellipse + partly circle
doubleyp=sin(lat[1-i])/sinw;
doublexp=sqrt(1.0-sqr(yp));
if(sinw<0)
{
xp=-xp;
}
M();
xy(-xp,yp);
arc(x[1-i],yd[1-i],0,
sin(lat[1-i])*cosw>0,cosw>=0);
xy(xp,yp);
arc(1,1,0,0,cosw>=0);
xy(-xp,yp);
Z();
}
elseif(h[2-2*i]<=0&&h[3-2*i]<=0)
{// stripe covers edge of the circle
circle(cosw<0);
}
}
}
if((h[0]*h[1]<0&&h[2]<=0&&h[3]<=0)
||(h[0]<=0&&h[1]<=0&&h[2]*h[3]<0))
{
// one slice visible
inti=h[0]<=0&&h[1]<=0;
doubleyp=sin(lat[i])/sinw;
doublexp=sqrt(1.0-yp*yp);
M();
xy(-xp,yp);
arc(x[i],yd[i],0,sin(lat[i])*cosw>0,cosw*sinw>=0);
xy(xp,yp);
arc(1,1,0,0,cosw*sinw<0);
xy(-xp,yp);
Z();
}
elseif(h[0]*h[1]<0&&h[2]*h[3]<0)
{
// disrupted ellipse bow
doublexp[2],yp[2];
for(inti=0;i<2;i++)
{
yp[i]=sin(lat[i])/sinw;
xp[i]=sqrt(1.0-sqr(yp[i]));
if(sinw<0)xp[i]=-xp[i];
}
M();
xy(-xp[0],yp[0]);
arc(x[0],yd[0],0,sin(lat[0])*cosw>0,cosw>=0);
xy(xp[0],yp[0]);
arc(1,1,0,0,0);
xy(xp[1],yp[1]);
arc(x[1],yd[1],0,sin(lat[1])*cosw>0,cosw<0);
xy(-xp[1],yp[1]);
arc(1,1,0,0,0);
xy(-xp[0],yp[0]);
Z();
}
cout<<"\" />\n";
}
}
for(inti=0;i<3;i++)
{
indent(--ind);
cout<<"</g>\n";
}
indent(ind--);
cout<<"<use id=\"sphere_front\" xlink:href=\"#sphere_half\" />\n";
end_svg_file();
}
