Cfrgtkky

Given two (A) and (B) 2-D points in tikzpicture environment, I need to collect both angle of the line (A)-(B) with respect to the vector(1,0) and the half of its distance in two variables, say Aab and Dab respectively. SOLVED (see Coordinates A, B: compute |B-A| and angle between +x and (B-A))

documentclass{article}

usepackage{pgf,tikz}

usetikzlibrary{calc}

makeatletter

newcommand{getLengthAndAngle}[2]{%

pgfmathanglebetweenpoints{pgfpointanchor{#1}{center}}

{pgfpointanchor{#2}{center}}

globalletmyanglepgfmathresult % we need a global macro

pgfpointdiff{pgfpointanchor{#1}{center}}

{pgfpointanchor{#2}{center}}

pgf@xa=pgf@x % no need to use a new dimen

pgf@ya=pgf@y

pgfmathparse{veclen(pgf@xa,pgf@ya)/28.45274} % to convert from pt 

 to cm

globalletmylengthpgfmathresult % we need a global macro}

makeatother 



begin{document}

    begin{tikzpicture}

    clip (0,4) rectangle (7,-5);

    coordinate (A) at (1,1);

    coordinate (B) at (3,4);

    getLengthAndAngle{A}{B}    

    draw[help lines,gray] (0,-3) grid (5,5);

    begin{scope}[blue, thick]  

    draw (A) -- (B)--+(mylength,0); 

    draw[rotate around={-myangle:(A)}] (A)--+(mylength,0);

    end{scope}

    draw (B) circle (mylength cm);

    end{tikzpicture} 

end{document}

Here is an alternative solely based on calc, i.e. not using extra macros, and with a little helper that allows you to "export" the length outside the path (and scope).

documentclass{article}

usepackage{pgf,tikz}

usetikzlibrary{calc}

begin{document}

    begin{tikzpicture}[globalize/.code n args={2}{xdef#2{#1}}]

    clip (0,4) rectangle (7,-5);

    coordinate (A) at (1,1);

    coordinate (B) at (3,4);

    draw[help lines,gray] (0,-3) grid (5,5);

    begin{scope}[blue, thick]  

    draw let p1=($(B)-(A)$), n1={veclen(y1,x1)}, n2={veclen(y1,x1)}

     in [globalize={n2}{mylength}] (A) -- (B)--+(n2,0)

     [rotate around={-n1:(A)}] (A)--+(n2,0);

    end{scope}

    draw (B) circle (mylength);

    end{tikzpicture} 

end{document}