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.project

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+<?xml version="1.0" encoding="UTF-8"?>
+<projectDescription>
+	<name>tikz-3dplot-circleofsphere</name>
+	<comment></comment>
+	<projects>
+	</projects>
+	<buildSpec>
+		<buildCommand>
+			<name>net.sourceforge.texlipse.builder.TexlipseBuilder</name>
+			<arguments>
+			</arguments>
+		</buildCommand>
+	</buildSpec>
+	<natures>
+		<nature>net.sourceforge.texlipse.builder.TexlipseNature</nature>
+	</natures>
+</projectDescription>

.texlipse

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+#TeXlipse project settings
+#Thu Jul 26 13:19:27 CEST 2018
+markTmpDer=true
+builderNum=2
+outputDir=
+makeIndSty=
+bibrefDir=
+outputFormat=pdf
+tempDir=
+mainTexFile=tikz-3dplot-circleofsphere.tex
+outputFile=tikz-3dplot-circleofsphere.pdf
+langSpell=en
+markDer=true
+srcDir=

_tester.tex

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+\documentclass{standalone}
+\usepackage[dvipsnames]{xcolor}
+\usepackage{tikz-3dplot-circleofsphere}
+
+\begin{document}
+
+  \def\elev{  30} \pgfmathsetmacro{\tdpTheta}{90-\elev}
+  \def\azim{  35} \pgfmathsetmacro{\tdpPhi}{90+\azim}
+  \def\R{3}
+  \tdplotsetmaincoords{\tdpTheta}{\tdpPhi}
+  \begin{tikzpicture}[scale=1,tdplot_main_coords]
+    \begin{scope}[black!30,name=auxiliary]
+      \draw[tdplot_screen_coords] (0,0,0) circle (\R);
+      \draw[->] (-1.3*\R,0,0) -- (1.3*\R,0,0) node[anchor=north east]{$x$};
+      \draw[->] (0,-1.3*\R,0) -- (0,1.3*\R,0) node[anchor=north west]{$y$};
+      \draw[->] (0,0,-1.3*\R) -- (0,0,1.3*\R) node[anchor=south]{$z$};
+      \tdplotCsDrawCircleOfSphere{\R}{0}{0}{0};
+    \end{scope}
+    \begin{scope}
+%      \tdplotCsDrawLatCircle[tdplotCsDrawAux]{\R}{-30}
+      % --
+      % Bug: Front and back side arcs swapped!
+      \tdplotCsDrawCircleOfSphere[tdplotCsDrawAux]{\R}{0}{30}{30}
+      % --
+%      \tdplotCsDrawCircleOfSphere[tdplotCsDrawAux]{\R}{-45}{45}{30}
+      % --
+%       \foreach \a in {0,15,...,345} 
+%         { \tdplotCsDrawCircleOfSphere[very thin,gray]{\R}{\a}{90}{0} }
+%       \foreach \a in {-75,-60,...,75} 
+%         { \tdplotCsDrawCircleOfSphere[very thin,gray]{\R}{0}{0}{\a} }
+      % -- Pathologic cases -->
+%       \tdplotCsDrawCircleOfSphere{\R}{35}{60}{0}
+      % <--
+    \end{scope}
+  \end{tikzpicture}
+
+\end{document}

examples/frontpage1.tex

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+\documentclass{standalone}
+\usepackage{tikz-3dplot-circleofsphere}
+\begin{document}
+  \centering
+  \def\R{3}
+  \tdplotsetmaincoords{60}{125}
+  \begin{tikzpicture}[tdplot_main_coords]
+    \draw[tdplot_screen_coords,very thin,gray] (0,0,0) circle (\R);
+    \tdplotCsDrawLatCircle%
+      [thick,tdplotCsFill/.style={opacity=0.05}]{\R}{0}
+    \tdplotCsDrawGreatCircle%
+      [red,thick,tdplotCsFill/.style={opacity=0.1}]{\R}{105}{-23.5}
+    \foreach \a in {-75,-60,...,75} 
+      {\tdplotCsDrawLatCircle[very thin,gray]{\R}{\a}}
+    \foreach \a in {0,15,...,165} 
+      {\tdplotCsDrawLonCircle[very thin,gray]{\R}{\a}}
+  \end{tikzpicture}
+\end{document}

examples/frontpage2.tex

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+\documentclass{standalone}
+\usepackage{tikz-3dplot-circleofsphere}
+\begin{document}
+  \centering
+  \def\R{3}
+  \tdplotsetmaincoords{60}{125}
+  \begin{tikzpicture}[tdplot_main_coords]
+    \def\e{80};
+    \draw[tdplot_screen_coords,very thin] (0,0,0) circle (\R);
+    \foreach \a in {0,5,...,175} {
+      \tdplotCsDrawGreatCircle%
+        [very thin, tdplotCsBack/.style={very thin,blue!40}]%
+        {\R}{\a}{90*sin(\a)*sin(\e)}
+    }
+  \end{tikzpicture}
+\end{document}

examples/minimalistcode.tex

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+\documentclass{standalone}
+\usepackage{tikz,tikz-3dplot}
+%% >> MINIMALIST CIRCLE OF SHPERE DRAWING CODE _______________________________________________________________________
+\newcommand\scircle[4]{%
+  \tdplotsetrotatedcoords{#2}{#3}{0}                                            % Rotate coordinate system
+  \let\a\tdplotalpha                                                            % alpha (rotated coord. system)
+  \let\b\tdplotbeta                                                             % beta (rotated coord. system)
+  \let\p\tdplotmainphi                                                          % phi (main coord. system)
+  \let\t\tdplotmaintheta                                                        % theta (main coord. system)
+  \pgfmathsetmacro\azx{cos(\a)*cos(\b)*sin(\p)*sin(\t) - sin(\b)*cos(\t) - cos(\b)*cos(\p)*sin(\a)*sin(\t)}
+  \pgfmathsetmacro\azy{-cos(\a)*cos(\p)*sin(\t) - sin(\a)*sin(\p)*sin(\t)}
+  \pgfmathsetmacro\azz{cos(\b)*cos(\t) + cos(\a)*sin(\b)*sin(\p)*sin(\t) - cos(\p)*sin(\a)*sin(\b)*sin(\t)}
+  \pgfmathsetmacro\Re {#1*cos(#4)}                                              % Radius of circle
+  \pgfmathsetmacro\ze {#1*sin(#4)}                                              % z-coordinate of drawing plane
+  \pgfmathsetmacro\coX{\ze*cos(#2)*sin(#3)}                                     % x-coordinate offset for ze
+  \pgfmathsetmacro\coY{\ze*sin(#2)*sin(#3)}                                     % y-coordinate offset for ze
+  \pgfmathsetmacro\coZ{\ze*cos(#3)}                                             % z-coordinate offset for ze
+  \coordinate (coffs) at (\coX,\coY,\coZ);                                      % Offset as coordinate value
+  \tdplotsetrotatedcoordsorigin{(coffs)}                                        % Offset coordinate system
+  \begin{scope}[tdplot_rotated_coords]                                          % Drawing scope >>
+    \pgfmathsetmacro\tanEps{tan(#4)}                                            %   Tangent of elevation angle
+    \pgfmathsetmacro\bOneside{((\tanEps)^2)>=(((\azx)^2+(\azy)^2)/(\azz)^2)}    %   Circle entirely on one side?
+    \ifthenelse{\bOneside=1}{%                                                  %   Circle on one side of sphere >>
+      \pgfmathsetmacro\bFrontside{(\azx*\Re+\azz*\ze)>=0}                       %     Circle entirely on front side?
+       \ifthenelse{\bFrontside=1}                                               %     |
+         {\draw (0,0) circle (\Re);}                                            %     Draw on front side
+         {\draw[dashed] (0,0) circle (\Re);}                                    %     Draw on back side
+    }{%                                                                         %   << Circle on both sides >>
+      \pgfmathsetmacro\u{\azy}                                                  %     Substitution u=...
+      \pgfmathsetmacro\v{sqrt( (\azx)^2 + (\azy)^2 - (\azz)^2*(\tanEps)^2 )}    %     Substitution v=...
+      \pgfmathsetmacro\w{\azx - \azz*\tanEps}                                   %     Substitution w=...
+      \pgfmathsetmacro\aPhiBf{2*atan2(\u-\v,\w)}                                %     Back->front crossing angle
+      \pgfmathsetmacro\aPhiFb{2*atan2(\u+\v,\w)}                                %     Front->back crossing angle
+      \pgfmathsetmacro\bUnwrap{(\aPhiFb-\aPhiBf)>360}                           %     Unwrap front->back angle?
+      \ifthenelse{\bUnwrap=1}{\pgfmathsetmacro\aPhiBf{\aPhiBf+360}}{}           %     Unwrap front->back angle
+      \draw[dashed] (\aPhiFb:\Re) arc (\aPhiFb:{\aPhiBf+360}:\Re);              %     Draw back side arc
+      \draw (\aPhiBf:\Re) arc (\aPhiBf:\aPhiFb:\Re);                            %     Draw back side arc
+    }                                                                           %   <<
+  \end{scope}                                                                   % << (Drawing scope)
+}
+%% << ________________________________________________________________________________________________________________
+\begin{document}
+  \tdplotsetmaincoords{60}{125}                                                 % Set main coordintate system
+  \begin{tikzpicture}[tdplot_main_coords]                                       % TikZ picture >>
+    \begin{scope}[black!30]                                                     %   Draw in gray >>
+      \draw[tdplot_screen_coords] (0,0,0) circle (3);                           %    Sphere outline
+      \scircle{3}{0}{0}{0}                                                      %    Equator
+    \end{scope}                                                                 %   <<
+    \scircle{3}{0}{40}{30}                                                    %   Draw another sphere circle
+  \end{tikzpicture}                                                             % <<
+\end{document}

tikz-3dplot-circleofsphere.bib

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+@Misc{Hei12,
+  author       = {Jeff Hein},
+  title        = {The \texttt{tikz-3dplot} Package},
+  howpublished = {Online: \url{https://mirror.hmc.edu/ctan/graphics/pgf/contrib/tikz-3dplot/tikz-3dplot_documentation.pdf}. Retrieved July 20, 2018},
+  year         = {2012}
+}
+
+@Misc{Tan15,
+  author       = {Till Tantau},
+  title        = {TikZ \& PGF - Manual for Version 3.0.1a},
+  howpublished = {Online: \url{https://mirror.reismil.ch/CTAN/graphics/pgf/base/doc/pgfmanual.pdf}. Retrieved July 22, 2018},
+  year         = {2015}
+}