Shift line connecting anchors

How can I shift a line the endpoints of which are defined by anchors like this?

\draw (i0) -- (i1);


The following approach does not work:

\draw[xshift=2pt] (i0) -- (i1);

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The question are ambiguous. You write anchors like anchors of node (tikz's notion) or you use another definition. I would like to know if anchors are coordinate \coordinate (i0) at (A.north west); or if anchors are nodes like in Marco's answer because the answer is not the same –  Alain Matthes Jan 2 '12 at 14:39

Approach 1

You can work with the library calc:

\draw[green] (i0) -- ($(i1)+(1,2)$);


Approach 2

Another approach based on the let operation. An example is given in the question TikZ: Node at same x-coordinate as another node, but specified y-coordinate?

\draw[blue] let \p1 = (i0) in (2,\y1) -- (i1);


Approach 3

Jake mentioned another approach. You set the shift to the coordinate directly. (this method is documented in the manual section 13 "Specifying Coordinates")

\draw ([xshift=2pt]i0) -- ([xshift=2pt]i1);


Note: By using this method will work fine if you define i0 and i1 with \coordinate. If you define i0 and i1 with \node you must give an anchor

\draw ([xshift=2pt]i0.center) -- ([xshift=2pt]i1.center);


This limitation isn't relevant for the other approaches.

Complete example with result

\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{calc}
\begin{document}
\verb+Calc+
\begin{tikzpicture}
\node at (0,0) (i0){};
\node at (2,2) (i1){};
\draw[red] (i0) -- (i1);
\draw[blue] ($(i0)+(2,0)$) -- (i1);
\draw[green] (i0) -- ($(i1)+(1,2)$);
\end{tikzpicture}

\verb+let+
\begin{tikzpicture}
\node at (0,0) (i0){};
\node at (2,2) (i1){};
\draw[red] (i0) -- (i1);
\draw[blue] let \p1 = (i0) in (2,\y1) -- (i1);
\draw[green] let \p1 = (i1) in (i0) -- (\x1,4);

\draw[black] let \p0 = (i0), \p1=(i1) in (\x0,2) -- (\x1,3);
\end{tikzpicture}

\verb+shift+ 1
\begin{tikzpicture}
\node at (0,0) (i0){};
\node at (2,2) (i1){};
\draw[red] (i0) -- (i1);
\draw[blue]([xshift=2cm]i0.center) --  (i1);
\draw[green] (i0) -- ([yshift=2cm,xshift=1cm]i1.center);
\end{tikzpicture}

\verb+shift+ 2
\begin{tikzpicture}
\coordinate (i0) at (0,0) ;
\coordinate (i1) at (2,2) ;
\draw[red] (i0) -- (i1);
\draw[blue]([xshift=2cm]i0) --  (i1);
\draw[green] (i0) -- ([yshift=2cm,xshift=1cm]i1);
\end{tikzpicture}
\end{document}


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A different approach would be to add the transformation to the coordinate specification (so \draw ([xshift=2pt]i1) -- ([xshift=2pt]i2);). Maybe you could flesh out your answer to show examples for all three approaches? –  Jake Jan 2 '12 at 11:38
I just tried the experiment and found that the syntax ([shift={(1,2)}]A) only works for positioning nodes. Strangely, ([shift={(1,2)}]0,0) works for arbitrary paths. I have no idea why this would be so, it seems rather illogical to me. –  Andrew Stacey Jan 2 '12 at 12:18
Ah, I see that the answer has been edited and that it works if an explicit anchor is given. This could be a bug in how the point-on-the-perimeter is computed for a translated node. Or one could say that translating a node coordinate without a specific anchor is open to different interpretations on which anchor should be used, so translating without an anchor should not be used. –  Andrew Stacey Jan 2 '12 at 12:22
@Altermundus and Marco Daniel: "anchors" are specified points on a shape, like north east, base west, 135, and so on. If you don't supply an anchor to a coordinate specification, but only a node name (like i0), an anchor on the edge the node that lies in the direction of the path is used. Only if i0 happens to be a node of the coordinate shape (created using \coordinate ... or \node [coordinate] ...), this is equivalent to the center anchor. So the original question is indeed ambiguous, as Altermundus noted. I guess it's another example of why MWEs are useful... –  Jake Jan 3 '12 at 9:33
(ctd) until they see the possible solutions, whereupon they will decide which behaviour they want and choose accordingly. –  Andrew Stacey Jan 3 '12 at 9:33

For me the shifting line is like the blue one

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{calc}
\begin{document}

\begin{tikzpicture}
\draw [help lines] (0,0) grid (3,2);
\node[draw](i0) at (0,0) {};
\node[draw](i1) at (2,2) {};
\draw[red] (i0) -- (i1) coordinate[pos=0] (j0) coordinate[pos=1] (j1);

\draw[thick,blue] ([xshift=1cm]j0) --  ([xshift=1cm]j1);
\draw[thick,purple] let \p0=(i0),\p1=(i1) in
([xshift=.5cm]\x0,\y0) --  ([xshift=.5cm]\x1,\y1);
\end{tikzpicture}

\end{document}


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