How can I use pgf from within TikZTransforming coordinates, so (0,0) from tikzpicture is put in the desired...

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How can I use pgf from within TikZ


Transforming coordinates, so (0,0) from tikzpicture is put in the desired place of the pageTikZ and PGF — Design considerations and approach to sizing pictures?How to calculate intersections of a line defined by a segment and an ellipse in tikzSpherical triangles and great circlesTikZ: Drawing an arc from an intersection to an intersectionDrawing rectilinear curves in Tikz, aka an Etch-a-Sketch drawingLine up nested tikz enviroments or how to get rid of themTikZ: “Clipping problem”Difference between an option's default and its initial valueuse of pgf intersections package for paths













3















Background: I understand that TikZ is built on top of pgf. Both are described in the pgf manual. However, I have been unable to find the section (if it exists at all) of the manual describing how the two are connected. This is a problem to me, as I enjoy the high level constructs of TikZ, yet I notice a number of useful primitives in pgf that I don't know how to access.



As an example, consider this simple picture:



two line segments and the intersection of their extensions



There are two short, non-intersecting line segments. The circle marks the point where the extended lines meet. The line segments and node labels were created with TikZ, the intersection with pgf.



Here is the code, lifted from the manual and adapted slightly:



documentclass[tikz]{standalone}
begin{document}
begin{tikzpicture}[x=20mm,y=20mm]
draw
(.5,0) node[left](A){$A$} -- (1,.8) node[left]{B}
(2,0) node[left](C){$C$} -- (1.5,1) node[right](D){D};
pgfpathcircle{%
pgfpointintersectionoflines
{pgfpointxy{.5}{0}}{pgfpointxy{1}{.8}}
{pgfpointxy{2}{0}}{pgfpointxy{1.5}{1}}}
{2pt}
pgfusepath{stroke}
end{tikzpicture}
end{document}


Clearly, the code is not DRY: The coordinates are repeated in the pgf section. But if the points A–D were them selves the result of calculations, this is not a viable option. Also, I can draw the intersection point, but I cannot use it in further work at the TikZ level. Hence my questions:





  • How do I represent the points A–D in terms that pgfpointintersectionoflines and other pgf constructs can use?

  • And how do I extract the result from the pgf world, for further use in the TikZ world?




Note that I am looking for answers that can be generalised, not a hack applying only to the present problem.










share|improve this question


















  • 1





    For the second part, seems you can do e.g. pgfcoordinate{foo}{ pgfpointintersectionoflines {pgfpointxy{.5}{0}}{pgfpointxy{1}{.8}} {pgfpointxy{2}{0}}{pgfpointxy{1.5}{1}}} to get a coordinate named foo at the intersection.

    – Torbjørn T.
    12 hours ago











  • @TorbjørnT. Indeed, that works. Thanks! (To be clear, it can then be referred to as (foo) later on.)

    – Harald Hanche-Olsen
    12 hours ago
















3















Background: I understand that TikZ is built on top of pgf. Both are described in the pgf manual. However, I have been unable to find the section (if it exists at all) of the manual describing how the two are connected. This is a problem to me, as I enjoy the high level constructs of TikZ, yet I notice a number of useful primitives in pgf that I don't know how to access.



As an example, consider this simple picture:



two line segments and the intersection of their extensions



There are two short, non-intersecting line segments. The circle marks the point where the extended lines meet. The line segments and node labels were created with TikZ, the intersection with pgf.



Here is the code, lifted from the manual and adapted slightly:



documentclass[tikz]{standalone}
begin{document}
begin{tikzpicture}[x=20mm,y=20mm]
draw
(.5,0) node[left](A){$A$} -- (1,.8) node[left]{B}
(2,0) node[left](C){$C$} -- (1.5,1) node[right](D){D};
pgfpathcircle{%
pgfpointintersectionoflines
{pgfpointxy{.5}{0}}{pgfpointxy{1}{.8}}
{pgfpointxy{2}{0}}{pgfpointxy{1.5}{1}}}
{2pt}
pgfusepath{stroke}
end{tikzpicture}
end{document}


Clearly, the code is not DRY: The coordinates are repeated in the pgf section. But if the points A–D were them selves the result of calculations, this is not a viable option. Also, I can draw the intersection point, but I cannot use it in further work at the TikZ level. Hence my questions:





  • How do I represent the points A–D in terms that pgfpointintersectionoflines and other pgf constructs can use?

  • And how do I extract the result from the pgf world, for further use in the TikZ world?




Note that I am looking for answers that can be generalised, not a hack applying only to the present problem.










share|improve this question


















  • 1





    For the second part, seems you can do e.g. pgfcoordinate{foo}{ pgfpointintersectionoflines {pgfpointxy{.5}{0}}{pgfpointxy{1}{.8}} {pgfpointxy{2}{0}}{pgfpointxy{1.5}{1}}} to get a coordinate named foo at the intersection.

    – Torbjørn T.
    12 hours ago











  • @TorbjørnT. Indeed, that works. Thanks! (To be clear, it can then be referred to as (foo) later on.)

    – Harald Hanche-Olsen
    12 hours ago














3












3








3








Background: I understand that TikZ is built on top of pgf. Both are described in the pgf manual. However, I have been unable to find the section (if it exists at all) of the manual describing how the two are connected. This is a problem to me, as I enjoy the high level constructs of TikZ, yet I notice a number of useful primitives in pgf that I don't know how to access.



As an example, consider this simple picture:



two line segments and the intersection of their extensions



There are two short, non-intersecting line segments. The circle marks the point where the extended lines meet. The line segments and node labels were created with TikZ, the intersection with pgf.



Here is the code, lifted from the manual and adapted slightly:



documentclass[tikz]{standalone}
begin{document}
begin{tikzpicture}[x=20mm,y=20mm]
draw
(.5,0) node[left](A){$A$} -- (1,.8) node[left]{B}
(2,0) node[left](C){$C$} -- (1.5,1) node[right](D){D};
pgfpathcircle{%
pgfpointintersectionoflines
{pgfpointxy{.5}{0}}{pgfpointxy{1}{.8}}
{pgfpointxy{2}{0}}{pgfpointxy{1.5}{1}}}
{2pt}
pgfusepath{stroke}
end{tikzpicture}
end{document}


Clearly, the code is not DRY: The coordinates are repeated in the pgf section. But if the points A–D were them selves the result of calculations, this is not a viable option. Also, I can draw the intersection point, but I cannot use it in further work at the TikZ level. Hence my questions:





  • How do I represent the points A–D in terms that pgfpointintersectionoflines and other pgf constructs can use?

  • And how do I extract the result from the pgf world, for further use in the TikZ world?




Note that I am looking for answers that can be generalised, not a hack applying only to the present problem.










share|improve this question














Background: I understand that TikZ is built on top of pgf. Both are described in the pgf manual. However, I have been unable to find the section (if it exists at all) of the manual describing how the two are connected. This is a problem to me, as I enjoy the high level constructs of TikZ, yet I notice a number of useful primitives in pgf that I don't know how to access.



As an example, consider this simple picture:



two line segments and the intersection of their extensions



There are two short, non-intersecting line segments. The circle marks the point where the extended lines meet. The line segments and node labels were created with TikZ, the intersection with pgf.



Here is the code, lifted from the manual and adapted slightly:



documentclass[tikz]{standalone}
begin{document}
begin{tikzpicture}[x=20mm,y=20mm]
draw
(.5,0) node[left](A){$A$} -- (1,.8) node[left]{B}
(2,0) node[left](C){$C$} -- (1.5,1) node[right](D){D};
pgfpathcircle{%
pgfpointintersectionoflines
{pgfpointxy{.5}{0}}{pgfpointxy{1}{.8}}
{pgfpointxy{2}{0}}{pgfpointxy{1.5}{1}}}
{2pt}
pgfusepath{stroke}
end{tikzpicture}
end{document}


Clearly, the code is not DRY: The coordinates are repeated in the pgf section. But if the points A–D were them selves the result of calculations, this is not a viable option. Also, I can draw the intersection point, but I cannot use it in further work at the TikZ level. Hence my questions:





  • How do I represent the points A–D in terms that pgfpointintersectionoflines and other pgf constructs can use?

  • And how do I extract the result from the pgf world, for further use in the TikZ world?




Note that I am looking for answers that can be generalised, not a hack applying only to the present problem.







tikz-pgf






share|improve this question













share|improve this question











share|improve this question




share|improve this question










asked 14 hours ago









Harald Hanche-OlsenHarald Hanche-Olsen

13.1k24762




13.1k24762








  • 1





    For the second part, seems you can do e.g. pgfcoordinate{foo}{ pgfpointintersectionoflines {pgfpointxy{.5}{0}}{pgfpointxy{1}{.8}} {pgfpointxy{2}{0}}{pgfpointxy{1.5}{1}}} to get a coordinate named foo at the intersection.

    – Torbjørn T.
    12 hours ago











  • @TorbjørnT. Indeed, that works. Thanks! (To be clear, it can then be referred to as (foo) later on.)

    – Harald Hanche-Olsen
    12 hours ago














  • 1





    For the second part, seems you can do e.g. pgfcoordinate{foo}{ pgfpointintersectionoflines {pgfpointxy{.5}{0}}{pgfpointxy{1}{.8}} {pgfpointxy{2}{0}}{pgfpointxy{1.5}{1}}} to get a coordinate named foo at the intersection.

    – Torbjørn T.
    12 hours ago











  • @TorbjørnT. Indeed, that works. Thanks! (To be clear, it can then be referred to as (foo) later on.)

    – Harald Hanche-Olsen
    12 hours ago








1




1





For the second part, seems you can do e.g. pgfcoordinate{foo}{ pgfpointintersectionoflines {pgfpointxy{.5}{0}}{pgfpointxy{1}{.8}} {pgfpointxy{2}{0}}{pgfpointxy{1.5}{1}}} to get a coordinate named foo at the intersection.

– Torbjørn T.
12 hours ago





For the second part, seems you can do e.g. pgfcoordinate{foo}{ pgfpointintersectionoflines {pgfpointxy{.5}{0}}{pgfpointxy{1}{.8}} {pgfpointxy{2}{0}}{pgfpointxy{1.5}{1}}} to get a coordinate named foo at the intersection.

– Torbjørn T.
12 hours ago













@TorbjørnT. Indeed, that works. Thanks! (To be clear, it can then be referred to as (foo) later on.)

– Harald Hanche-Olsen
12 hours ago





@TorbjørnT. Indeed, that works. Thanks! (To be clear, it can then be referred to as (foo) later on.)

– Harald Hanche-Olsen
12 hours ago










2 Answers
2






active

oldest

votes


















3














In addition to what Torbjørn T. says you can use existing nodes/coordinates with pgfpointanchor{<name>}{<anchor>}.



documentclass[tikz]{standalone}
begin{document}
begin{tikzpicture}[x=20mm,y=20mm]
draw
(.5,0) node[left](A){$A$} -- (1,.8) node[left](B){B}
(2,0) node[left](C){$C$} -- (1.5,1) node[right](D){D};
pgfcoordinate{aux}{pgfpointintersectionoflines
{pgfpointanchor{A}{east}}{pgfpointanchor{B}{east}}
{pgfpointanchor{C}{east}}{pgfpointanchor{D}{west}}}
pgfpathcircle{pgfpointanchor{aux}{center}}{2pt}
pgfusepath{stroke}
draw (aux) -- (aux|-A.south);
end{tikzpicture}
end{document}


enter image description here






share|improve this answer
























  • Thanks, that is useful. But I had just realised, before seeing your answer, that I messed up a little: I should have let (A) refer to coordinates, not anchors. I.e., I should have used (.5,0) coordinate(A) node{$A$} and similarly for the other points. And then, all the pgfpointanchor macros can be given {center} as their second argument.

    – Harald Hanche-Olsen
    9 hours ago











  • @HaraldHanche-Olsen You haven't "messed up" I think.;-)

    – marmot
    9 hours ago



















1














I did come up with another solution myself. It is not as nice as marmot's answer, but as it is a different approach to the same problem, possibly enabling a different set of options, I offer it here, for the record:



documentclass[tikz]{standalone}
usetikzlibrary{math}
begin{document}
begin{tikzpicture}[x=20mm,y=20mm]
draw
(.5,0) coordinate(A) node[left]{$A$} -- (1,.8) coordinate(B) node[left]{B}
(2,0) coordinate(C) node[left]{$C$} -- (1.5,1) coordinate(D) node[right]{D};
tikzmath{
coordinate A; A = (A);
coordinate B; B = (B);
coordinate C; C = (C);
coordinate D; D = (D); }
pgfcoordinate{E}{
pgfpointintersectionoflines
{pgfpoint{Ax}{Ay}}{pgfpoint{Bx}{By}}
{pgfpoint{Cx}{Cy}}{pgfpoint{Dx}{Dy}}}
draw (E) circle[radius=2pt];
end{tikzpicture}
end{document}


In the process of getting there, I learned the difference between pgfpoint (canvas coordinates?) and pgfpointxy (user coordinates).






share|improve this answer
























  • I knew you would go for tikzmath ;-)

    – marmot
    9 hours ago











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2 Answers
2






active

oldest

votes








2 Answers
2






active

oldest

votes









active

oldest

votes






active

oldest

votes









3














In addition to what Torbjørn T. says you can use existing nodes/coordinates with pgfpointanchor{<name>}{<anchor>}.



documentclass[tikz]{standalone}
begin{document}
begin{tikzpicture}[x=20mm,y=20mm]
draw
(.5,0) node[left](A){$A$} -- (1,.8) node[left](B){B}
(2,0) node[left](C){$C$} -- (1.5,1) node[right](D){D};
pgfcoordinate{aux}{pgfpointintersectionoflines
{pgfpointanchor{A}{east}}{pgfpointanchor{B}{east}}
{pgfpointanchor{C}{east}}{pgfpointanchor{D}{west}}}
pgfpathcircle{pgfpointanchor{aux}{center}}{2pt}
pgfusepath{stroke}
draw (aux) -- (aux|-A.south);
end{tikzpicture}
end{document}


enter image description here






share|improve this answer
























  • Thanks, that is useful. But I had just realised, before seeing your answer, that I messed up a little: I should have let (A) refer to coordinates, not anchors. I.e., I should have used (.5,0) coordinate(A) node{$A$} and similarly for the other points. And then, all the pgfpointanchor macros can be given {center} as their second argument.

    – Harald Hanche-Olsen
    9 hours ago











  • @HaraldHanche-Olsen You haven't "messed up" I think.;-)

    – marmot
    9 hours ago
















3














In addition to what Torbjørn T. says you can use existing nodes/coordinates with pgfpointanchor{<name>}{<anchor>}.



documentclass[tikz]{standalone}
begin{document}
begin{tikzpicture}[x=20mm,y=20mm]
draw
(.5,0) node[left](A){$A$} -- (1,.8) node[left](B){B}
(2,0) node[left](C){$C$} -- (1.5,1) node[right](D){D};
pgfcoordinate{aux}{pgfpointintersectionoflines
{pgfpointanchor{A}{east}}{pgfpointanchor{B}{east}}
{pgfpointanchor{C}{east}}{pgfpointanchor{D}{west}}}
pgfpathcircle{pgfpointanchor{aux}{center}}{2pt}
pgfusepath{stroke}
draw (aux) -- (aux|-A.south);
end{tikzpicture}
end{document}


enter image description here






share|improve this answer
























  • Thanks, that is useful. But I had just realised, before seeing your answer, that I messed up a little: I should have let (A) refer to coordinates, not anchors. I.e., I should have used (.5,0) coordinate(A) node{$A$} and similarly for the other points. And then, all the pgfpointanchor macros can be given {center} as their second argument.

    – Harald Hanche-Olsen
    9 hours ago











  • @HaraldHanche-Olsen You haven't "messed up" I think.;-)

    – marmot
    9 hours ago














3












3








3







In addition to what Torbjørn T. says you can use existing nodes/coordinates with pgfpointanchor{<name>}{<anchor>}.



documentclass[tikz]{standalone}
begin{document}
begin{tikzpicture}[x=20mm,y=20mm]
draw
(.5,0) node[left](A){$A$} -- (1,.8) node[left](B){B}
(2,0) node[left](C){$C$} -- (1.5,1) node[right](D){D};
pgfcoordinate{aux}{pgfpointintersectionoflines
{pgfpointanchor{A}{east}}{pgfpointanchor{B}{east}}
{pgfpointanchor{C}{east}}{pgfpointanchor{D}{west}}}
pgfpathcircle{pgfpointanchor{aux}{center}}{2pt}
pgfusepath{stroke}
draw (aux) -- (aux|-A.south);
end{tikzpicture}
end{document}


enter image description here






share|improve this answer













In addition to what Torbjørn T. says you can use existing nodes/coordinates with pgfpointanchor{<name>}{<anchor>}.



documentclass[tikz]{standalone}
begin{document}
begin{tikzpicture}[x=20mm,y=20mm]
draw
(.5,0) node[left](A){$A$} -- (1,.8) node[left](B){B}
(2,0) node[left](C){$C$} -- (1.5,1) node[right](D){D};
pgfcoordinate{aux}{pgfpointintersectionoflines
{pgfpointanchor{A}{east}}{pgfpointanchor{B}{east}}
{pgfpointanchor{C}{east}}{pgfpointanchor{D}{west}}}
pgfpathcircle{pgfpointanchor{aux}{center}}{2pt}
pgfusepath{stroke}
draw (aux) -- (aux|-A.south);
end{tikzpicture}
end{document}


enter image description here







share|improve this answer












share|improve this answer



share|improve this answer










answered 11 hours ago









marmotmarmot

105k4126241




105k4126241













  • Thanks, that is useful. But I had just realised, before seeing your answer, that I messed up a little: I should have let (A) refer to coordinates, not anchors. I.e., I should have used (.5,0) coordinate(A) node{$A$} and similarly for the other points. And then, all the pgfpointanchor macros can be given {center} as their second argument.

    – Harald Hanche-Olsen
    9 hours ago











  • @HaraldHanche-Olsen You haven't "messed up" I think.;-)

    – marmot
    9 hours ago



















  • Thanks, that is useful. But I had just realised, before seeing your answer, that I messed up a little: I should have let (A) refer to coordinates, not anchors. I.e., I should have used (.5,0) coordinate(A) node{$A$} and similarly for the other points. And then, all the pgfpointanchor macros can be given {center} as their second argument.

    – Harald Hanche-Olsen
    9 hours ago











  • @HaraldHanche-Olsen You haven't "messed up" I think.;-)

    – marmot
    9 hours ago

















Thanks, that is useful. But I had just realised, before seeing your answer, that I messed up a little: I should have let (A) refer to coordinates, not anchors. I.e., I should have used (.5,0) coordinate(A) node{$A$} and similarly for the other points. And then, all the pgfpointanchor macros can be given {center} as their second argument.

– Harald Hanche-Olsen
9 hours ago





Thanks, that is useful. But I had just realised, before seeing your answer, that I messed up a little: I should have let (A) refer to coordinates, not anchors. I.e., I should have used (.5,0) coordinate(A) node{$A$} and similarly for the other points. And then, all the pgfpointanchor macros can be given {center} as their second argument.

– Harald Hanche-Olsen
9 hours ago













@HaraldHanche-Olsen You haven't "messed up" I think.;-)

– marmot
9 hours ago





@HaraldHanche-Olsen You haven't "messed up" I think.;-)

– marmot
9 hours ago











1














I did come up with another solution myself. It is not as nice as marmot's answer, but as it is a different approach to the same problem, possibly enabling a different set of options, I offer it here, for the record:



documentclass[tikz]{standalone}
usetikzlibrary{math}
begin{document}
begin{tikzpicture}[x=20mm,y=20mm]
draw
(.5,0) coordinate(A) node[left]{$A$} -- (1,.8) coordinate(B) node[left]{B}
(2,0) coordinate(C) node[left]{$C$} -- (1.5,1) coordinate(D) node[right]{D};
tikzmath{
coordinate A; A = (A);
coordinate B; B = (B);
coordinate C; C = (C);
coordinate D; D = (D); }
pgfcoordinate{E}{
pgfpointintersectionoflines
{pgfpoint{Ax}{Ay}}{pgfpoint{Bx}{By}}
{pgfpoint{Cx}{Cy}}{pgfpoint{Dx}{Dy}}}
draw (E) circle[radius=2pt];
end{tikzpicture}
end{document}


In the process of getting there, I learned the difference between pgfpoint (canvas coordinates?) and pgfpointxy (user coordinates).






share|improve this answer
























  • I knew you would go for tikzmath ;-)

    – marmot
    9 hours ago
















1














I did come up with another solution myself. It is not as nice as marmot's answer, but as it is a different approach to the same problem, possibly enabling a different set of options, I offer it here, for the record:



documentclass[tikz]{standalone}
usetikzlibrary{math}
begin{document}
begin{tikzpicture}[x=20mm,y=20mm]
draw
(.5,0) coordinate(A) node[left]{$A$} -- (1,.8) coordinate(B) node[left]{B}
(2,0) coordinate(C) node[left]{$C$} -- (1.5,1) coordinate(D) node[right]{D};
tikzmath{
coordinate A; A = (A);
coordinate B; B = (B);
coordinate C; C = (C);
coordinate D; D = (D); }
pgfcoordinate{E}{
pgfpointintersectionoflines
{pgfpoint{Ax}{Ay}}{pgfpoint{Bx}{By}}
{pgfpoint{Cx}{Cy}}{pgfpoint{Dx}{Dy}}}
draw (E) circle[radius=2pt];
end{tikzpicture}
end{document}


In the process of getting there, I learned the difference between pgfpoint (canvas coordinates?) and pgfpointxy (user coordinates).






share|improve this answer
























  • I knew you would go for tikzmath ;-)

    – marmot
    9 hours ago














1












1








1







I did come up with another solution myself. It is not as nice as marmot's answer, but as it is a different approach to the same problem, possibly enabling a different set of options, I offer it here, for the record:



documentclass[tikz]{standalone}
usetikzlibrary{math}
begin{document}
begin{tikzpicture}[x=20mm,y=20mm]
draw
(.5,0) coordinate(A) node[left]{$A$} -- (1,.8) coordinate(B) node[left]{B}
(2,0) coordinate(C) node[left]{$C$} -- (1.5,1) coordinate(D) node[right]{D};
tikzmath{
coordinate A; A = (A);
coordinate B; B = (B);
coordinate C; C = (C);
coordinate D; D = (D); }
pgfcoordinate{E}{
pgfpointintersectionoflines
{pgfpoint{Ax}{Ay}}{pgfpoint{Bx}{By}}
{pgfpoint{Cx}{Cy}}{pgfpoint{Dx}{Dy}}}
draw (E) circle[radius=2pt];
end{tikzpicture}
end{document}


In the process of getting there, I learned the difference between pgfpoint (canvas coordinates?) and pgfpointxy (user coordinates).






share|improve this answer













I did come up with another solution myself. It is not as nice as marmot's answer, but as it is a different approach to the same problem, possibly enabling a different set of options, I offer it here, for the record:



documentclass[tikz]{standalone}
usetikzlibrary{math}
begin{document}
begin{tikzpicture}[x=20mm,y=20mm]
draw
(.5,0) coordinate(A) node[left]{$A$} -- (1,.8) coordinate(B) node[left]{B}
(2,0) coordinate(C) node[left]{$C$} -- (1.5,1) coordinate(D) node[right]{D};
tikzmath{
coordinate A; A = (A);
coordinate B; B = (B);
coordinate C; C = (C);
coordinate D; D = (D); }
pgfcoordinate{E}{
pgfpointintersectionoflines
{pgfpoint{Ax}{Ay}}{pgfpoint{Bx}{By}}
{pgfpoint{Cx}{Cy}}{pgfpoint{Dx}{Dy}}}
draw (E) circle[radius=2pt];
end{tikzpicture}
end{document}


In the process of getting there, I learned the difference between pgfpoint (canvas coordinates?) and pgfpointxy (user coordinates).







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answered 9 hours ago









Harald Hanche-OlsenHarald Hanche-Olsen

13.1k24762




13.1k24762













  • I knew you would go for tikzmath ;-)

    – marmot
    9 hours ago



















  • I knew you would go for tikzmath ;-)

    – marmot
    9 hours ago

















I knew you would go for tikzmath ;-)

– marmot
9 hours ago





I knew you would go for tikzmath ;-)

– marmot
9 hours ago


















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