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I'm trying to draw something like this: enter image description here

How would I go about it in tikZ? For example, how do I draw the curved gray manifold?

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It depends how accurate you want the rendering to be. It is simple enough to draw something that looks okay, but you need to remember that TikZ/PGF is fundamentally a 2D system and so getting lighting and so forth exactly right is going to be ... complicated. – Loop Space Nov 5 '12 at 11:18
As a starting point \shade[left color=white,right color=gray] (0,0) to[bend left] (1,-0.5) -- (2,1) to[bend right] (1,2) -- cycle; I'm completely guessing the numbers. – percusse Nov 5 '12 at 11:21
Mh, 3d-curved manifold? Isn't it rather a surface (2d)? – c.p. Nov 6 '12 at 0:46
@JorgeCampos: You're right, it is a surface. On it, one would only need $\mathbb{R}^2$. I meant that because it's curved someone not on it might describe it in $\mathbb{R}^3$ – mac389 Nov 7 '12 at 7:43
up vote 19 down vote accepted

Here's one possibility:





% the bottom left border of the surface
\path[name path=border1] (0,0) to[out=-10,in=150] (6,-2);
% the upper right border of the surface
\path[name path=border2] (12,1) to[out=150,in=-10] (5.5,3.2);
% a path for a line crossing both borders
\path[name path=redline] (0,-0.4) -- (12,1.5);
% intersections between the borders and the lines
\path[name intersections={of=border1 and redline,by={a}}];
\path[name intersections={of=border2 and redline,by={b}}];

% we draw the surface
\shade[left color=gray!10,right color=gray!80] 
  (0,0) to[out=-10,in=150] (6,-2) -- (12,1) to[out=150,in=-10] (5.5,3.7) -- cycle;
% we draw the red line
\draw[red,line width=1.5pt,shorten >= 3pt,shorten <= 3pt] 
  (a) .. controls (6,-0.2) and (5,3.5) ..
  coordinate[pos=0.22] (cux1) 
  coordinate[pos=0.57] (cux2) 
  coordinate[pos=0.88] (cux3) (b);
% we draw the curved black line on top
\draw (-0.3,3.5) to[out=-10,in=225] 
  coordinate[pos=0.27] (aux1) 
  coordinate[pos=0.52] (aux2) 
  coordinate[pos=0.75] (aux3) (10,7.5);
% we draw the dashed line on the surface
\draw[dashed] (a) .. controls (6,1.5) and (7,2) .. 
  coordinate[pos=0.2] (bux1) 
  coordinate[pos=0.5] (bux2) 
  coordinate[pos=0.8] (bux3) (b);

% we draw the dashed lines from the curved line on top to the 
% dashed line on the surface
\foreach \coor in {1,2,3}
  \draw[dashed] (aux\coor)to[bend left] (bux\coor);
% we draw the markers on the top line and place the labels
\foreach \coor/\subs in {1/-1,2/,3/1}
  \draw[fill=white] (aux\coor) circle (3pt);
  \node[label=above:$t_{\subs}$] at (aux\coor) {};
% we draw the filled red circles on the red line
\foreach \coor in {1,2,3}
  \draw[fill=red] (cux\coor) circle (3pt);
% we draw the filled black circles near the red line
\draw[fill] ([xshift=-20pt,yshift=10pt]cux1) circle (3pt);
\draw[fill] ([xshift=20pt,yshift=-10pt]cux2) circle (3pt);
\draw[fill] ([xshift=5pt,yshift=-15pt]cux3) circle (3pt);

%  we place the "x" labels
\node (dux1) [xshift=30pt,yshift=-15pt,font=\sffamily,rotate=30] at (cux1) {x};
\node (dux2) [xshift=-24pt,yshift=12pt,font=\sffamily,rotate=30] at (cux2) {x};
\node (dux3) [xshift=-30pt,yshift=15pt,font=\sffamily,rotate=30] at (cux3) {x};

% we draw the blue and gray arrows
every node/.style={
  inner sep=0pt,
  single arrow,
  single arrow head extend=2pt}
\node[fill=black!70,anchor=west,rotate=152,xshift=5pt] at (dux1) 
\node[fill=black!70,anchor=west,rotate=-25,xshift=5pt] at (dux2) 
\node[fill=black!70,anchor=west,rotate=-25,xshift=5pt] at (dux3) 

\node[fill=blue!70,anchor=west,rotate=-2,xshift=10pt] at (a) 
\node[fill=blue!70,anchor=west,rotate=48,xshift=10pt] at (cux1) 
\node[fill=blue!70,anchor=west,rotate=22,xshift=10pt] at (cux2) 

% we add some labels
\node[rotate=30] at (6.2,-1.5) {$E_r$};
\node[rotate=30] at (9.2,6) {$E_N$};
\node[font=\color{red}] at (10,2.2) {MAP};

\node at ([yshift=-1cm]current bounding box.south) {
\tikz\draw (0,0) circle (2pt); & Underlying model & \sffamily x & Prediction \\ 
\tikz\draw[fill=red] (0,0) circle (2pt); & Filter (MAP estimate) 
  & \tikz\draw[fill] (0,0) circle (2pt); & MLE



enter image description here

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