TikZ PGF – How to Draw an Infinitesimal Portion of a Surface

diagramstikz-pgf

I'm trying to draw the following figures using TikZ, and I've found some issues :

Here's my attempt :

    \begin{tikzpicture}
\def\a{2} 
\def\b{1} 
\def\h{6}
\draw[->] (0,0)--(-\a,0) node[midway, above]{$r$};
\filldraw (0,0) circle(1pt); 
\filldraw (0,\h) circle(1pt); 
\draw[dashed, ->] (0,\h)--(0,\h+2) node[left] {$d\vec{S}$};
\draw[blue, thick] (\a,0)--(\a,\h) (-\a,0)--(-\a,\h);
\draw[dashed,blue, thick] (\a,0) arc [x radius=\a, y radius=\b, start angle=0, end angle=180];
\draw[blue, thick] (-\a,0) arc [x radius=\a, y radius=\b, start angle=180, end angle=360];
\draw[blue, thick]  (0,\h) ellipse (\a cm and \b cm);
\draw[->] (0,\h)--(3,\h) node[above, midway] {$\vec{E}$}; 
\draw[ultra thick] (0,0)--(0,\h) node[midway, left] {$\lambda >0$};
\end{tikzpicture}

And I need to draw some other figures, such as :

My problem is always that surface portion. Any thoughts ?

Best Answer

Old notation: circle(1pt) and new notation: circle[radius=1 pt]. You make me anxious when you mix them.

\documentclass[tikz, border=1 cm]{standalone}
\begin{document}
\begin{tikzpicture}
\def\a{2} 
\def\b{1} 
\def\h{6}
\draw[->] (0,0)--(-\a,0) node[midway, above]{$r$};
\filldraw (0,0) circle[radius=1 pt]; 
\filldraw (0,\h) circle[radius=1 pt]; 
\draw[dashed, ->] (0,\h)--(0,\h+2) node[left] {$d\vec{S}$};
\draw[blue, thick] (\a,0)--(\a,\h) (-\a,0)--(-\a,\h);
\draw[dashed,blue, thick] (\a,0) arc[x radius=\a, y radius=\b, start angle=0, end angle=180];
\draw[blue, thick] (-\a,0) arc[x radius=\a, y radius=\b, start angle=180, end angle=360];
\draw[blue, thick]  (0,\h) ellipse[x radius=\a, y radius=\b];
\draw[->] (0,\h)--(3,\h) node[above, midway] {$\vec{E}$}; 
\draw[ultra thick] (0,0)--(0,\h) node[midway, left] {$\lambda >0$};
\draw[red, thick, fill=pink, opacity=0.5]
  ({\a*cos(-80)},{\b*sin(-80)+4}) arc[x radius=\a, y radius=\b, start angle=-80, end angle=-60] --
  ({\a*cos(-60)},{\b*sin(-60)+3.4}) arc[x radius=\a, y radius=\b, start angle=-60, end angle=-80] -- cycle;
\draw[red, thick, ->] ({\a*cos(-70)},{\b*sin(-70)+3.7}) -- ({2*\a*cos(-70)},{2*\b*sin(-70)+3.7}) node[above right, midway]{$\vec{E}$};
\end{tikzpicture}
\end{document}

Related Solutions

[Tex/LaTex] Drawing rectilinear curves in Tikz, aka an Etch-a-Sketch drawing

\draw (20,12) -- ++(2,0) -- ++(0,2) -- ++(-3,0) -- ++(45:3);

Use ++ before each new incremental coordinate to make it relative to the last one and put the pencil there.

Here's a complete example:

\documentclass{article}
\usepackage{tikz}
\begin{document}
\tikz\draw (20,12) -- ++(2,0) -- ++(0,2) -- ++(-3,0) -- ++(30:3) {[rounded corners=10pt]-- ++(5,0) -- ++(0,-6)} -- ++(-7,0) -- cycle;
\end{document}

Of course, combining this with the -| or |- path operators can simplify the code even further; the following two pieces of code produce the same result:

\tikz\draw (20,12) -- ++(2,0) -- ++(0,2) -- ++(3,0) -- ++(0,1) -- ++(1,0) -- ++(0,-3) -- ++(2,0);\par\bigskip

and

\tikz\draw (20,12) -| ++(2,2) -| ++(3,1) -- ++(1,0) |- ++(2,-3);

I don't think that defining commands in this case adds anything; in fact, I think it reduces the functionality of the existing syntax (which is already simple). The example demonstrates that you can use, for example, polar coordinates and modify (up to TikZ limitations) the path attributes midways; even if the current question doesn't require this, it's a good thing to have the possibility to do those kind of modification if they are required.

TikZ-PGF – Creating a Document Header with TikZ

\documentclass[tikz,border=2pt]{standalone}
\usetikzlibrary{chains, positioning, shapes.symbols}
\usepackage{xcolor}
\definecolor{darkblue}{RGB}{9,72,90}
\definecolor{lightblue}{RGB}{124,184,201}

\begin{document}
\begin{tikzpicture}[
    node distance = 2pt,
    start chain = going right,
    start/.style = {signal, 
                    draw=darkblue, 
                    fill=lightblue,
                    text width=2cm, 
                    minimum height=1cm, 
                    font=\scriptsize,
                    text=white,
                    signal pointer angle=120, on chain},
    cont/.style = {start, 
                    signal from=west}
    ]
    
    \node[start,](a) {\bfseries Construction de l'image};
    \node[above=0.6cm of a.west, anchor=south west,
            rectangle, 
            draw=darkblue, 
            fill=darkblue,
            minimum height=2cm,
            minimum width=13cm,
            text=white,
            inner sep=1pt]
            (titre){\large{La photographie numérique}};
    \node[cont] {\bfseries Métadonnées EXIF};
    \node[cont](b) {\bfseries Step3};
    \node[right=5.4cm of titre.north east, anchor=north east,
            rectangle,
            draw=darkblue,
            fill=darkblue,thick,
            rounded corners,
            minimum height=3cm,
            text width=5cm,
            text=white]
            (competences){Identifier les étapes de la construction de l'image finale};
\end{tikzpicture}
\end{document}

Best Answer

Related Solutions

[Tex/LaTex] Drawing rectilinear curves in Tikz, aka an Etch-a-Sketch drawing

TikZ-PGF – Creating a Document Header with TikZ

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