11

I need to make quite a few "first-angle projection" in Tikz (see Wikipedia ) for an exercise sheet, so I was wondering if there is a routine to make them?

By this I mean that I could give a certain number of 3d coordinates for points, define the edges (and perhaps the surfaces too) and then get the 6 required planar projections (without having to change each time the code for the planar coordinates of the projected points, ideally without having to specify which edges/surfaces are above the other).

Of course, the solution for just one planar projection would be enough...

Here is an example of such a solid. Of course I could write the planar projections by hand, but that would be very tedious to do that for all the others again.

\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{calc}
\begin{document}
\tikzset{
MyPersp/.style={scale=1,x={(-0.35355cm,-0.35355cm)},y={(1cm,0cm)}, z={(0cm,1cm)}}
}
\begin{tikzpicture}[line cap=round, rounded corners=.1mm,MyPersp]
 % vertices
\coordinate (A) at (0,0,0);
\coordinate (B) at (2,0,0);
\coordinate (C) at (2,2,0);
\coordinate (D) at (0,2,0);
\coordinate (E1) at (0,0,1);
\coordinate (E2) at (0,1,2);
\coordinate (E3) at (1,0,2);
\coordinate (F) at (2,0,2);
\coordinate (G) at (2,2,2);
\coordinate (H) at (0,2,2);
% edges and surfaces
\fill[white,opacity=.5,draw=black,thick] (A) -- (D) -- (H) -- (E2) -- (E1) -- (A);
\fill[white,opacity=.5,draw=black,thick] (A) -- (B) -- (C) -- (D) -- (A);
\fill[white,opacity=.5,draw=black,thick] (E1) -- (E2) -- (E3) -- (E1);
\fill[white,opacity=.5,draw=black,thick] (A) -- (B) -- (F) -- (E3) -- (E1) -- (A);
\fill[white,opacity=.5,draw=black,thick] (C) -- (D) -- (H) -- (G) -- (C);
\fill[white,opacity=.5,draw=black,thick] (B) -- (C) -- (G) -- (F) -- (B);
\fill[white,opacity=.5,draw=black,thick] (F) -- (G) -- (H) -- (E2) -- (E3) -- (F);
% names
\draw (A) node{A};
\draw (B) node{B};
\draw (C) node{C};
\draw (D) node{D};
\draw (F) node{F};
\draw (G) node{G};
\draw (H) node{H};
\end{tikzpicture}
\end{document}
  • 1
    An orthographic projection can be done similar as your MyPersp style (Sidenote: your projection is not a perspective view but a cabinet projection). You can use a style orthographic view/.style={x={(0cm,0cm)},y={(1cm,0cm)},z={(0cm,1cm)}} and define views by rotating around axes, e.g. left view/.style={orthographic view,rotate around z=90}. Note that commands that are issued later still get drawn on top, even if they should be in the back with the current view. – Max Aug 31 '18 at 9:02
  • Ver nice, but there are still a few problems: 1- I need to start a new tikzpicture and redefine the coordinates (i.e. copy and paste) for each projection. How do I use these "views" inside a scope (I tried "\begin{scope}[left view, transform canvas={xshift = 5cm}]" and it did not work). 2- I need to change the order of the drawing of the faces in each new view individually. In my example, the left and the right view will both be respresented as squares (if you put opacity to 1), because the last side to be drawn is the square one. This is still a lot of tedious case checking... – ARG Aug 31 '18 at 10:30
  • Please see my answer below. That should be a more convenient method than the styles from my comment. – Max Aug 31 '18 at 10:32
11

Using Tikz, there is no easy way to determine what to draw and what is hidden behind other faces. Fortunately, the pgfplots package is capable of exactly that:

enter image description here

\documentclass[tikz,margin=2mm]{standalone}
\usepackage{tikz,pgfplots,pgfplotstable,filecontents}

\usepgfplotslibrary{patchplots}

\pgfplotsset{compat=1.16,
    projection/.style={
        hide axis,
        enlargelimits=false,
        scale only axis,
        width=4cm,
        height=4cm,
        axis equal,
        view={115}{30},
        clip=false,
    },
    front view/.style={projection,view={90}{0},title={Front view}},
    back view/.style={projection,view={-90}{0},title={Back view}},
    right view/.style={projection,view={180}{0},title={Right view}},
    left view/.style={projection,view={0}{0},title={Left view}},
    top view/.style={projection,view={90}{90},title={Top view}},
    bottom view/.style={projection,view={90}{-90},title={Bottom view}},
    patch plot style/.style={
        patch,
        patch type=polygon,
        vertex count=5,
        patch table with point meta={PatchesTable.dat},
        white,
        opacity=0.5,
        thick,
        faceted color=black,
    },
}

\begin{filecontents*}{PatchesTable.dat}
%pt1 pt2 pt3 pt4 pt5 meta
   0   3   9   5   4    1 % (A)  -- (D)  -- (H)  -- (E2) -- (E1) -- (A);
   0   1   2   3   3    1 % (A)  -- (B)  -- (C)  -- (D)  -- (A);
   4   5   6   6   6    1 % (E1) -- (E2) -- (E3) -- (E1);
   0   1   7   6   4    1 % (A)  -- (B)  -- (F)  -- (E3) -- (E1) -- (A);
   2   3   9   8   8    1 % (C)  -- (D)  -- (H)  -- (G)  -- (C);
   1   2   8   7   1    1 % (B)  -- (C)  -- (G)  -- (F)  -- (B);
   7   8   9   5   6    1 % (F)  -- (G)  -- (H)  -- (E2) -- (E3) -- (F);
\end{filecontents*}
\begin{filecontents*}{PointsTable.dat}
    x y z
    0 0 0 % 0 (A) 
    2 0 0 % 1 (B) 
    2 2 0 % 2 (C) 
    0 2 0 % 3 (D) 
    0 0 1 % 4 (E1)
    0 1 2 % 5 (E2)
    1 0 2 % 6 (E3)
    2 0 2 % 7 (F) 
    2 2 2 % 8 (G) 
    0 2 2 % 9 (H) 
\end{filecontents*}

\begin{document}

\pgfplotstableread{PointsTable.dat}\PointsTable

\begin{tikzpicture}
    \begin{axis}[projection,at={(5cm,5cm)}]
        \addplot3 [patch plot style] table {\PointsTable};
    \end{axis}

    \foreach \view/\x/\y in {
        left view/-5/0,
        front view/0/0,
        right view/5/0,
        back view/10/0,
        top view/0/5,
        bottom view/0/-5
    }{
        \begin{axis}[\view,at={(\x cm,\y cm)}]
            \addplot3 [patch plot style] table {\PointsTable};
        \end{axis}
    }
\end{tikzpicture}
\end{document}

Edit
Because we use Tikz and pgfplots to make things look stunning, I had to try marmot's comment. This indeed looks very nice, and it made me discover that the right view and back view are not entirely correct. This seems to be due to the painter's algorithm that pgfplots uses to determine what is one top. An (ugly) fix to this could be to change the right and back view to:

back view/.style={projection,view={-90}{0.02},title={Back view}},
right view/.style={projection,view={180}{0.02},title={Right view}},

Thus with a very small elevation angle. This very slightly stretches the line widths of the horizontal lines, but does help the drawing order. The results is:

enter image description here

  • 3
    That's really great! If you remove white from the patch plot style and give the third face a different meta, say 2, the result looks even more spectacular IMHO. – user121799 Aug 31 '18 at 12:51
  • 1
    ah... thanks for the fix! I was trying this out and noted the right/back view problem. Also, the color improvement is really great! "we use Tikz and pgfplots to make things look stunning" Amen! – ARG Aug 31 '18 at 13:42
  • Small bug? when I run your code I always get a "finished with exit code 1" error... – ARG Aug 31 '18 at 13:48
  • @ARG I can't reproduce, and I don't know what that error means. – Max Aug 31 '18 at 13:51
  • @Max: no worries, found it. My compiler did not know what you meant with "compat=1.16". I probably just need to update to the latest Ubuntu version... Many thanks again for this awesome solution! – ARG Aug 31 '18 at 14:54
4

This is not an answer, but work in progress and to pay tribute to Max' stellar answer: a partly successful attempt to arrange the projections in a 3D-like manner around the shape. (UPDATE: Fixed the alignment of some texts, big thanks to ARG!)

\documentclass[tikz,margin=2mm]{standalone}
\usepackage{tikz,tikz-3dplot,pgfplots,pgfplotstable,filecontents}
\usetikzlibrary{3d}
% small fix for canvas is xy plane at z % https://tex.stackexchange.com/a/48776/121799
\makeatletter
\tikzoption{canvas is xy plane at z}[]{%
    \def\tikz@plane@origin{\pgfpointxyz{0}{0}{#1}}%
    \def\tikz@plane@x{\pgfpointxyz{1}{0}{#1}}%
    \def\tikz@plane@y{\pgfpointxyz{0}{1}{#1}}%
    \tikz@canvas@is@plane}
\makeatother

\newsavebox\mybox
\newsavebox\mainbox
\usepgfplotslibrary{patchplots}

\pgfplotsset{compat=1.16,
    projection/.style={
        hide axis,
        enlargelimits=false,
        scale only axis,
        width=4cm,
        height=4cm,
        axis equal,
        view={115}{30},
        clip=false,
    },
    front view/.style={projection,view={90}{0},title={Front view}},
    %back view/.style={projection,view={-90}{0},title={Back view}},
    %right view/.style={projection,view={180}{0},title={Right view}},
    left view/.style={projection,view={0}{0},title={Left view}},
    top view/.style={projection,view={90}{-90},title={Top view},
    title style={at={(0.5,-0.25)},yscale=-1}},
    bottom view/.style={projection,view={90}{-90},title={Bottom view},
    title style={at={(0.5,-0.25)},scale=-1}},
    back view/.style={projection,view={90}{0},title={Back view},
    title style={xscale=-1}}, % adjusted
    right view/.style={projection,view={0}{0.02},title={Right view},
    title style={xscale=-1}},    
    patch plot style/.style={
        patch,
        patch type=polygon,
        vertex count=5,
        patch table with point meta={PatchesTable.dat},
        %white,
        opacity=0.2,
        thick,
        faceted color=black,
    },
}

\begin{filecontents*}{PatchesTable.dat}
%pt1 pt2 pt3 pt4 pt5 meta
   0   3   9   5   4    1 % (A)  -- (D)  -- (H)  -- (E2) -- (E1) -- (A);
   0   1   2   3   3    1 % (A)  -- (B)  -- (C)  -- (D)  -- (A);
   4   5   6   6   6    2 % (E1) -- (E2) -- (E3) -- (E1);
   0   1   7   6   4    1 % (A)  -- (B)  -- (F)  -- (E3) -- (E1) -- (A);
   2   3   9   8   8    1 % (C)  -- (D)  -- (H)  -- (G)  -- (C);
   1   2   8   7   1    1 % (B)  -- (C)  -- (G)  -- (F)  -- (B);
   7   8   9   5   6    1 % (F)  -- (G)  -- (H)  -- (E2) -- (E3) -- (F);
\end{filecontents*}
\begin{filecontents*}{PointsTable.dat}
    x y z
    0 0 0 % 0 (A) 
    2 0 0 % 1 (B) 
    2 2 0 % 2 (C) 
    0 2 0 % 3 (D) 
    0 0 1 % 4 (E1)
    0 1 2 % 5 (E2)
    1 0 2 % 6 (E3)
    2 0 2 % 7 (F) 
    2 2 2 % 8 (G) 
    0 2 2 % 9 (H) 
\end{filecontents*}

\begin{document}

\pgfplotstableread{PointsTable.dat}\PointsTable

\begin{tikzpicture}
    \begin{lrbox}{\mainbox}
    \begin{axis}[projection]
        \addplot3 [patch plot style] table {\PointsTable};
    \end{axis}
    \end{lrbox}
\tdplotsetmaincoords{115}{-30}
\path[use as bounding box] (-5,-5) rectangle (5,5);
\begin{scope}[tdplot_main_coords]

    \foreach \view/\x/\y/\Canvas in {
        left view/x/-2.5/yz,
        back view/y/-2.5/xz,
        bottom view/z/-2.5/xy%
    }{
        \begin{lrbox}{\mybox}
        \begin{axis}[\view]
            \addplot3 [patch plot style] table {\PointsTable};
        \end{axis}
        \end{lrbox}
        \begin{scope}[canvas is \Canvas\space plane at \x=\y,transform shape]
          \node[scale=0.75] at (0,0) {\usebox{\mybox}};
        \end{scope}
    }
    %
    \begin{scope}[canvas is xz plane at y=3]
          \node at (0,0) {\usebox{\mainbox}};
    \end{scope}
    %
    \foreach \view/\x/\y/\Canvas in {
        front view/y/5/xz,
        right view/x/5/yz,
        top view/z/5/xy%
    }{
        \begin{lrbox}{\mybox}
        \begin{axis}[\view]
            \addplot3 [patch plot style] table {\PointsTable};
        \end{axis}
        \end{lrbox}
        \begin{scope}[canvas is \Canvas\space plane at \x=\y,
        transform shape]
          \node[scale=0.75] at
          (0,0) {\usebox{\mybox}};
        \end{scope}
    }
\end{scope} 
\end{tikzpicture}
\end{document}

enter image description here

  • 1
    +1 Nice! And now we wait for the animation of the virtual box unfolding :) – Max Sep 2 '18 at 9:08
  • 1
    very cool! it's a very nice example of stunning things to do with tikz! – ARG Sep 2 '18 at 12:05
  • Hey, I actually found a small problem: the rigth view is identical to the left view. This goes also for top and bottom as well as front and back. It's not dramatix, it's just that the edges which should be soft (because they are hidden) are strong, and vice-versa. I had to fix this by returning to the previous views and use xscale=-1 (or yscale=-1) in order to mirror them. But now the text for the corresponding view is way off. Any idea how to solve this without going into too much trouble? – ARG Sep 12 '18 at 11:28
  • @ARG I tried to fix it, is this what you want? And yes, the views in 3D are a bit tricky. I was actually surprised to see that one can get that far so easily. Of course, if you start shifting and flipping things, you will feel the full effects of the non-Abelian nature of the 3D Euclidean group. ;-) – user121799 Sep 12 '18 at 14:25
  • 1
    For the record: Jake's patch is now incorporated in v3.1 of TikZ. – Stefan Pinnow Jan 15 at 18:59

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