Tips for creating semi-random blob in tikz

Question

I am somewhat starting to get acustomed to tikz now. But I am trying to reproduce the image below in tikz

I have managed to make the triangle (I think?) using tikz, now I have no idea how to make the woobbly part around the image. I did look into such things as parabolas, but did not make it work. I did som reading about beltzier curves, however that left me even more puzzled.

My code so far

 \documentclass{article}
 \usepackage{mathtools}
 \usepackage{amsfonts}
 \usepackage{amssymb}
 \usepackage{amsmath}
 \usepackage{tikz}
 \usetikzlibrary{calc}
 \usetikzlibrary{backgrounds}
 \usepgflibrary{shapes}
 \usetikzlibrary{through}
 \usetikzlibrary{arrows}
 \usepackage{tkz-euclide}
 \usetkzobj{all}
 \begin{document}

 \begin{tikzpicture}[scale=1.4,label]
 \tkzInit[xmin=-1 , xmax=14 , ymin=-1 , ymax=5]
 \tkzClip
 \tkzDefPoint(0,0){A} \tkzDefPoint(10,0){B}  
 \tkzDefPointBy[rotation= center B angle -15.4](A)
 \tkzGetPoint{C}
 \tkzDefPointBy[rotation= center A angle  69.7](B)
 \tkzGetPoint{D}
 \tkzDrawSegment[very thick](A,B)
 \tkzInterLL(A,D)(C,B) \tkzGetPoint{I}
 \tkzDrawSegments[dashed](A,I I,B)
 \tkzDefMidPoint(A,I) \tkzGetPoint{M}
 \tkzMarkAngle[scale=0.75,dashed](A,I,B)
 \tkzMarkAngle[scale=0.75,dashed](B,A,I)
 \tkzDrawPoints[color=black,shape=circle,fill=red,size=10pt](A,I,B)
 \tkzLabelPoint[left](M){$40.0m$} 
 \tkzLabelPoint[right](B){\Large $B$} 
 \tkzLabelPoint[left](A){\Large $A$} 
 \tkzLabelPoint[above left](I){\Large $C$} 
 \tkzLabelAngle[pos=0.8](A,I,B){ $94.9^{\circ}$ }
 \tkzLabelAngle[pos=0.9 ](B,A,I){ $69.7^{\circ}$ }
 \end{tikzpicture}

 \end{document}     

Could someone please hint or show how to produce an somewhat arbitary shaded blob / polygon in latex? Another problem is that my blob needs to look as close as possible to the one in the image above.

Answer 1

You can use the random steps decoration from the decorations.pathmorphing library, combined with rounded corners to create something similar.

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{decorations.pathmorphing}
\usepackage{tkz-euclide}
\usetkzobj{all}
\begin{document}

 \begin{tikzpicture}[label]
 \tkzInit[xmin=-1.5 , xmax=14 , ymin=-3 , ymax=5]
 \tkzClip
 \tkzDefPoint(0,0){A} \tkzDefPoint(10,0){B}  
 \tkzDefPointBy[rotation= center B angle -15.4](A)
 \tkzGetPoint{C}
 \tkzDefPointBy[rotation= center A angle  69.7](B)
 \tkzGetPoint{D}
 \tkzDrawSegment[very thick](A,B)
 \tkzInterLL(A,D)(C,B) \tkzGetPoint{I}
 \tkzDrawSegments[dashed](A,I I,B)
 \tkzDefMidPoint(A,I) \tkzGetPoint{M}
 \tkzMarkAngle[scale=0.75,dashed](A,I,B)
 \tkzMarkAngle[scale=0.75,dashed](B,A,I)
 \tkzDrawPoints[color=black,shape=circle,fill=red,size=10pt](A,I,B)
 \tkzLabelPoint[left](M){40.0\,m} 
 \tkzLabelPoint[right](B){\Large $B$} 
 \tkzLabelPoint[left](A){\Large $A$} 
 \tkzLabelPoint[above left](I){\Large $C$} 
 \tkzLabelAngle[pos=0.8](A,I,B){ $94.9^{\circ}$ }
 \tkzLabelAngle[pos=0.9 ](B,A,I){ $69.7^{\circ}$ }
 \draw [shade,
        top color=blue,
        bottom color=white,
        fill opacity=.1,
        decoration={random steps,segment length=1cm,amplitude=.5cm},
        decorate,
        rounded corners=.3cm]
     (A) -- (0.4,0.7)  -- (5,3.1) -- (B) -- (10,-1) -- (1.6,-1.5) -- (A);
 \end{tikzpicture}

 \end{document}

As the effect of the decoration is somewhat, well, random, your output may differ from this.

---

If the blob has to be almost identical to the one in your image, it would perhaps be easier to draw the path manually in e.g. Inkscape and export to TikZ code with inkscape2tikz. (There may be other tools that allow you to do this, but I knew about these, so that's what I used.)

The code isn't exactly pretty, and I had to shift and scale it manually to make it fit with the existing drawing, but that didn't take too long.

\documentclass{article}
\usepackage{tikz}
\usepackage{tkz-euclide}
\usetkzobj{all}
\begin{document}

 \begin{tikzpicture}[label]
 \tkzInit[xmin=-1.5 , xmax=14 , ymin=-3 , ymax=5]
 \tkzClip
 \tkzDefPoint(0,0){A} \tkzDefPoint(10,0){B}  
 \tkzDefPointBy[rotation= center B angle -15.4](A)
 \tkzGetPoint{C}
 \tkzDefPointBy[rotation= center A angle  69.7](B)
 \tkzGetPoint{D}
 \tkzDrawSegment[very thick](A,B)
 \tkzInterLL(A,D)(C,B) \tkzGetPoint{I}
 \tkzDrawSegments[dashed](A,I I,B)
 \tkzDefMidPoint(A,I) \tkzGetPoint{M}
 \tkzMarkAngle[scale=0.75,dashed](A,I,B)
 \tkzMarkAngle[scale=0.75,dashed](B,A,I)
 \tkzDrawPoints[color=black,shape=circle,fill=red,size=10pt](A,I,B)
 \tkzLabelPoint[left](M){40.0\,m} 
 \tkzLabelPoint[right](B){\Large $B$} 
 \tkzLabelPoint[left](A){\Large $A$} 
 \tkzLabelPoint[above left](I){\Large $C$} 
 \tkzLabelAngle[pos=0.8](A,I,B){ $94.9^{\circ}$ }
 \tkzLabelAngle[pos=0.9 ](B,A,I){ $69.7^{\circ}$ }
 \begin{scope}[x=0.01cm,y=-0.01cm,shift={(-67,-380)},scale=1.18]
  \path[draw=black,
        shade,
        top color=blue,
        bottom color=white,
        fill opacity=.1] (324.2857,37.4286) .. controls (324.2857,37.4286)
    and (375.7143,8.8571) .. (402.8571,8.8571) .. controls (537.1429,8.8571) and
    (594.9022,229.4892) .. (645.7143,237.4286) .. controls (691.4286,244.5714) and
    (687.1428,196.0000) .. (732.8571,196.0000) .. controls (761.5711,196.0000) and
    (819.9039,267.6222) .. (854.2857,284.5714) .. controls (872.0828,293.3449) and
    (898.1530,287.6641) .. (904.2857,310.2857) .. controls (908.4648,325.7012) and
    (915.4588,428.9108) .. (880.9086,428.5105) .. controls (859.7549,428.2654) and
    (847.9021,422.6772) .. (834.2857,418.8571) .. controls (820.2451,414.9181) and
    (814.2857,393.1429) .. (782.8571,390.2857) .. controls (751.4286,387.4286) and
    (711.4514,402.4931) .. (680.0000,401.7143) .. controls (622.3075,400.2857) and
    (496.2045,334.2248) .. (450.4902,341.3677) .. controls (404.7759,348.5105) and
    (370.8368,402.6229) .. (326.5511,406.8368) .. controls (282.3729,411.0405) and
    (224.1124,380.4590) .. (176.9695,380.4590) .. controls (129.8267,380.4590) and
    (114.2857,408.8571) .. (102.8571,408.8571) .. controls (91.4286,408.8571) and
    (43.7959,397.5021) .. (43.8673,366.6635) .. controls (43.9391,335.6534) and
    (128.3263,212.2045) .. (158.3263,199.3474) .. controls (188.3263,186.4902) and
    (228.5714,164.5714) .. (237.1429,153.1429) .. controls (245.7143,141.7143) and
    (231.4286,86.0000) .. (254.2857,71.7143) .. controls (277.1429,57.4286) and
    (324.2857,37.4286) .. (324.2857,37.4286) -- cycle;
\end{scope}
\end{tikzpicture}

\end{document}