Draw Shadow to a plan

Question

I want to draw something like this picture:

As the shadow is curved, i decided to draw a trapezium and then draw a shadow on it. The problem is i want the coordinates of the trapezium corners. here is my code

\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{shapes.geometric}

\usetikzlibrary{shadows}
\usetikzlibrary{shapes.symbols}
\definecolor{mycolor}{rgb}{0.55,0.9,0.55}
\begin{document}
\begin{tikzpicture}[y=.3cm, x=1.2cm,font=\sffamily]
%\node[circle,fill=black] at (0,0) {};
\node[circle,fill=black] at (5.59,-8.3) {};
\node[circle,fill=black] at (-2.1,-8.3) {};
\node[circle,fill=black] at (-5.59,8.3) {};
%rotate = -140
\node[trapezium, minimum width=10cm,trapezium left angle=130, trapezium right angle=50, minimum height = 5cm,fill=mycolor]  at (0,0){};

\filldraw[fill=gray]
(5.55,-8.3) -- (5.55,-8) -- (-2.1,-8) -- (-5.6,8) -- (-5.59,8.3) -- (-2.1,-8.3) -- cycle;

\end{tikzpicture}
\end{document}

I tried to figure out the coordinates by drawing circles in the arbitrary locations and correct them manually.

Is there away to find these coordinates accurately?, and am i thinking a hard way and there is an easy way to do this?.

Answer 1

You can draw the shape inside a pic definition, and then use that pic to reuse the figure at any place/scale/angle. This pic feature requires a recent version of Tikz/PGF.

This is an example:

\documentclass{article}
\usepackage{tikz}

\tikzset{
  patch/.pic = {
    \draw[fill=green!30] (-2,0) to[out=10, in=190] (0,1)
            to (2,0)
            to[out=-140, in=45] (0,-1)
            to[out=145, in=-35] (-2,0)
            -- cycle;
    \draw[fill=black!60] (0,-1) 
            to[out=145, in=-35] (-2,0)
            -- (-2,-.2) -- (0,-1.5) -- cycle;
    \draw[fill=black!30] (2,0)        
            to[out=-140, in=45] (0,-1)
            -- (0,-1.5) -- (2, -.2) -- cycle;
    },
}  

\begin{document}
\begin{tikzpicture}
\pic at (0,0) {patch};
\pic[scale=0.5, rotate=20] at (2,2) {patch};
\pic[scale=0.5, rotate=-20] at (-2,2) {patch};
\end{tikzpicture}
\end{document}

This is the result: