gnuplot-info

[Gnuplot-info] Question on Plots on Non-regular Grid

[Lorenzo I. <lor...@gm...>]

Dear All,
I am fairly new to data plotting and visualization.
My problem should be simple, but it is not straightforward to tackle in 
R or Python.
On the cross section of a pipe (i.e. on a circle) I have a temperature 
reading of the kind: T=T(r,theta).
I would like to make a 2D contour plot using colors such that one can see
that the domain where I am plotting is actually a circle.
Furthermore, I do not have necessarily an equally spaced grid.
For instance, let me consider the case of 5 theta's and 7 radial
position and consequently 35 values of T (just a simple test):

         theta                             
R                                                                T
0.000000000000000000e+00 0.000000000000000000e+00 5.459815003314423620e+01
0.000000000000000000e+00 1.666666666666666574e-01 4.853828855239110851e+01
0.000000000000000000e+00 3.333333333333333148e-01 4.315101251901344881e+01
0.000000000000000000e+00 5.000000000000000000e-01 3.836167151642037965e+01
0.000000000000000000e+00 6.666666666666666297e-01 3.410390059527122020e+01
0.000000000000000000e+00 8.333333333333332593e-01 3.031870066752165016e+01
0.000000000000000000e+00 1.000000000000000000e+00 2.695362096775039973e+01
1.570796326794896558e+00 0.000000000000000000e+00 2.396203225329512776e+01
1.570796326794896558e+00 1.666666666666666574e-01 2.130248067207563523e+01
1.570796326794896558e+00 3.333333333333333148e-01 1.893811334477913277e+01
1.570796326794896558e+00 5.000000000000000000e-01 1.683616770181326316e+01
1.570796326794896558e+00 6.666666666666666297e-01 1.496751749887080329e+01
1.570796326794896558e+00 8.333333333333332593e-01 1.330626922033307302e+01
1.570796326794896558e+00 1.000000000000000000e+00 1.182940327795447999e+01
3.141592653589793116e+00 0.000000000000000000e+00 1.051645503298913731e+01
3.141592653589793116e+00 1.666666666666666574e-01 9.349231221746512333e+00
3.141592653589793116e+00 3.333333333333333148e-01 8.311557855141172624e+00
3.141592653589793116e+00 5.000000000000000000e-01 7.389056098930650407e+00
3.141592653589793116e+00 6.666666666666666297e-01 6.568943029058285532e+00
3.141592653589793116e+00 8.333333333333332593e-01 5.839854501207304871e+00
3.141592653589793116e+00 1.000000000000000000e+00 5.191687680104649871e+00
4.712388980384689674e+00 0.000000000000000000e+00 4.615461046534314882e+00
4.712388980384689674e+00 1.666666666666666574e-01 4.103189942205120566e+00
4.712388980384689674e+00 3.333333333333333148e-01 3.647775927922803252e+00
4.712388980384689674e+00 5.000000000000000000e-01 3.242908421924544982e+00
4.712388980384689674e+00 6.666666666666666297e-01 2.882977255397825012e+00
4.712388980384689674e+00 8.333333333333332593e-01 2.562994933482758420e+00
4.712388980384689674e+00 1.000000000000000000e+00 2.278527524544009530e+00
6.283185307179586232e+00 0.000000000000000000e+00 2.025633220058637107e+00
6.283185307179586232e+00 1.666666666666666574e-01 1.800807713756398032e+00
6.283185307179586232e+00 3.333333333333333148e-01 1.600935643142084031e+00
6.283185307179586232e+00 5.000000000000000000e-01 1.423247420534685892e+00
6.283185307179586232e+00 6.666666666666666297e-01 1.265280855439646635e+00
6.283185307179586232e+00 8.333333333333332593e-01 1.124847036463023642e+00
6.283185307179586232e+00 1.000000000000000000e+00 1.000000000000000000e+00



How would you plot them in order to have a 2D-color plot where one can
understand we are working on a circle (well, maybe it will look like
something different since I have only a few grid points, but the aim
is clear, I hope)?
Despite its simplicity, this has been taking me a long time and I am not 
done yet. Someone has recently suggested to learn VTK, but it may be too 
much for what I have in mind.
Anyone who can give me a simple script to read that data and get a 
contour plot on a pipe's cross section would help  me a lot (I am sure 
it must amount to a few lines).
Kind Regards

Lorenzo

Re: [Gnuplot-info] Question on Plots on Non-regular Grid

[Thomas S. <t.s...@fz...>]

a contour plot is not so easy unless you have your data on a grid.
re-binning a few data points into a grid with 'dgrid3d' doesn't work.

so, either you have a reasonable number of data points - so many,
that 'set dgrid3d' works - or you do the re-binning (= filling a
2d-histogram)
outside of gnuplot.
or, for a very low number of data points, a 'poor man's' solution could be:

set xrange [-1:1]
set yrange [-1:1]
set view map
set mapping cyl
splot 'datafile' using 1:3:2 with points pointtype 5 pointsize 3 palette


Lorenzo Isella wrote:
> 
> Dear All,
> I am fairly new to data plotting and visualization.
> My problem should be simple, but it is not straightforward to tackle in 
> R or Python.
> On the cross section of a pipe (i.e. on a circle) I have a temperature 
> reading of the kind: T=T(r,theta).
> I would like to make a 2D contour plot using colors such that one can see
> that the domain where I am plotting is actually a circle.
> Furthermore, I do not have necessarily an equally spaced grid.
> For instance, let me consider the case of 5 theta's and 7 radial
> position and consequently 35 values of T (just a simple test):
> 
>          theta                             
> R                                                                T
> 0.000000000000000000e+00 0.000000000000000000e+00 5.459815003314423620e+01
> 0.000000000000000000e+00 1.666666666666666574e-01 4.853828855239110851e+01
> 0.000000000000000000e+00 3.333333333333333148e-01 4.315101251901344881e+01
> 0.000000000000000000e+00 5.000000000000000000e-01 3.836167151642037965e+01
> 0.000000000000000000e+00 6.666666666666666297e-01 3.410390059527122020e+01
> 0.000000000000000000e+00 8.333333333333332593e-01 3.031870066752165016e+01
> 0.000000000000000000e+00 1.000000000000000000e+00 2.695362096775039973e+01
> 1.570796326794896558e+00 0.000000000000000000e+00 2.396203225329512776e+01
> 1.570796326794896558e+00 1.666666666666666574e-01 2.130248067207563523e+01
> 1.570796326794896558e+00 3.333333333333333148e-01 1.893811334477913277e+01
> 1.570796326794896558e+00 5.000000000000000000e-01 1.683616770181326316e+01
> 1.570796326794896558e+00 6.666666666666666297e-01 1.496751749887080329e+01
> 1.570796326794896558e+00 8.333333333333332593e-01 1.330626922033307302e+01
> 1.570796326794896558e+00 1.000000000000000000e+00 1.182940327795447999e+01
> 3.141592653589793116e+00 0.000000000000000000e+00 1.051645503298913731e+01
> 3.141592653589793116e+00 1.666666666666666574e-01 9.349231221746512333e+00
> 3.141592653589793116e+00 3.333333333333333148e-01 8.311557855141172624e+00
> 3.141592653589793116e+00 5.000000000000000000e-01 7.389056098930650407e+00
> 3.141592653589793116e+00 6.666666666666666297e-01 6.568943029058285532e+00
> 3.141592653589793116e+00 8.333333333333332593e-01 5.839854501207304871e+00
> 3.141592653589793116e+00 1.000000000000000000e+00 5.191687680104649871e+00
> 4.712388980384689674e+00 0.000000000000000000e+00 4.615461046534314882e+00
> 4.712388980384689674e+00 1.666666666666666574e-01 4.103189942205120566e+00
> 4.712388980384689674e+00 3.333333333333333148e-01 3.647775927922803252e+00
> 4.712388980384689674e+00 5.000000000000000000e-01 3.242908421924544982e+00
> 4.712388980384689674e+00 6.666666666666666297e-01 2.882977255397825012e+00
> 4.712388980384689674e+00 8.333333333333332593e-01 2.562994933482758420e+00
> 4.712388980384689674e+00 1.000000000000000000e+00 2.278527524544009530e+00
> 6.283185307179586232e+00 0.000000000000000000e+00 2.025633220058637107e+00
> 6.283185307179586232e+00 1.666666666666666574e-01 1.800807713756398032e+00
> 6.283185307179586232e+00 3.333333333333333148e-01 1.600935643142084031e+00
> 6.283185307179586232e+00 5.000000000000000000e-01 1.423247420534685892e+00
> 6.283185307179586232e+00 6.666666666666666297e-01 1.265280855439646635e+00
> 6.283185307179586232e+00 8.333333333333332593e-01 1.124847036463023642e+00
> 6.283185307179586232e+00 1.000000000000000000e+00 1.000000000000000000e+00
> 
> 
> 
> How would you plot them in order to have a 2D-color plot where one can
> understand we are working on a circle (well, maybe it will look like
> something different since I have only a few grid points, but the aim
> is clear, I hope)?
> Despite its simplicity, this has been taking me a long time and I am not 
> done yet. Someone has recently suggested to learn VTK, but it may be too 
> much for what I have in mind.
> Anyone who can give me a simple script to read that data and get a 
> contour plot on a pipe's cross section would help  me a lot (I am sure 
> it must amount to a few lines).
> Kind Regards
> 
> Lorenzo
> 
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Re: [Gnuplot-info] Question on Plots on Non-regular Grid

[<HBB...@t-...>]

Lorenzo Isella wrote:

> I am fairly new to data plotting and visualization.

> I would like to make a 2D contour plot using colors such that one can see
> that the domain where I am plotting is actually a circle.

That's going to be a little tricky.  In particular, the seam where theta 
jumps by 2*pi will be apparent in the plot.

> Furthermore, I do not have necessarily an equally spaced grid.

It doesn't have to equally spaced as long as it's topologically 
rectangular, i.e. consists of N rows of M entries.  You have to inform 
gnuplot about where one row ends and the next one begins.  See 'help 
glossary' and 'help datafile' and watch out for 'grid structure'.