How to plot (x,y,z) points showing their density

Question

My data file is a set of (x,y,z) points located around the axis origin. They represent points where a kind of measure has failed. These points are in this link.

Gnuplot can plot them,

set encoding iso_8859_1
set term postscript eps enhanced color size 4.7in,4in
set xlabel "X"
set ylabel "Y"
set zlabel "Z"
set output "test_gp.eps"
set style line 1 lc rgb '#0060ad' pt 7 ps 0.5 lt 1 lw 0.5 # --- blue
set style fill  transparent solid 0.15 noborder
splot "data.dat" u 1:2:3 w p ls 1 title "P_{error}"

with the resulting plot

The problem is that the figure does not show where the error is more likely to occur. I would like to show the variations in the density of points if it is possible.

I do not know if it is possible to vary the color of the points or give them transparency and try to represent the locations with the most density of points.

If a representation of the density of 3D points is not possible, another way could be to make a projection density of the points in the three planes (x=0,y,z), (x,y=0,z), (x,y,z=0).

Regards

EDIT:

I can plot with different colors the success (0) and error (1) point locations of my experiment. The file in this link has a 4th column with all data samples ( 0's and 1's).

The splot figure

splot "data_all.dat" u 1:2:3:4 w points ls 1 palette title "P_{error}"

is

but this figure is not showing the density of points. For example, in Mathematica the density plot of these data samples is

How could I get the density plot with Gnuplot?. It is likely that Mathematica is doing an interpolation of the points in the middle and give them values between 0 and 1, but I do not know how to achieve it with Gnuplot.

with your code your datapoints are not transparent. Instead set linecolor for example to rgb '#cc0060ad', according to the scheme #aarrggbb. aa will be the alpha channel. About calculating the density, I don't know how Mathematica does it or how it could be done in gnuplot but basically it is counting the points in a certain small volume and assigning a color to it. This reminds me to smooth frequency and binning, but in 3D. — theozh
@theozh I believe this is not possible in Gnuplot. I can make a 2D density plot making a matrix. Each position of the matrix is a xy bin (a 2D bin), and the value is the count of xy numbers that fall in that 2D bin. In link stackoverflow.com/questions/46159983/… The solution shows how to generate that matrix of numbers from a xy data samples. With the matrix is possible to make the heatmap like in the first example of gnuplot.sourceforge.net/demo/heatmaps.html — user1993416
@theozh The problem here is similar but with 3D bins are more difficult to generate, and there is no example of doing 3D heatmaps with Gnuplot. Therefore, I believe Gnuplot does not implement a way to do it. A workaround would be make a heat map for the three coordinates planes (x,y, z=0), (x,y=0, z), (x =0 ,y, z). And represent the three heatmaps together in the XYZ coordinates system (like projections). I can generate the three heat maps (although I did not try it yet I believe is possible), but I do not know how to join the three of them in the coordinates system. — user1993416

theozh theozh · Accepted Answer · 2018-12-12T13:31:23

@user1993416, I guess you can do something with gnuplot. You might need to play with the parameter Delta. With my 8 year old computer 1000 points need approx. 2 minutes.

The followig code:

### 3D density plot
reset session
set term wxt

N = 1000      # number of datapoints
Delta = 2    # half boxwidth

TimeStart = time(0.0)
# create dummy some dummy data
set samples N
set table $Data
    plot '+' u (invnorm(rand(0))):(invnorm(rand(0))):(invnorm(rand(0))) with table
unset table

# put the datafile/dataset into arrays
stats $Data nooutput
RowCount = STATS_records
array ColX[RowCount]
array ColY[RowCount]
array ColZ[RowCount]
array ColC[RowCount]
do for [i=1:RowCount] {
set table $Dummy
    plot $Data u (ColX[$0+1]=$1,0):(ColY[$0+1]=$2,0):(ColZ[$0+1]=$3,0) with table
unset table
}

# look at each datapoint and its sourrounding
do for [i=1:RowCount] {
    print sprintf("Datapoint %g of %g",i,RowCount)
    x0 = ColX[i]
    y0 = ColY[i]
    z0 = ColZ[i]
    # count the datapoints with distances <Delta around the datapoint of interest
    set table $Occurrences
        plot $Data u ((abs(x0-$1)<Delta) & (abs(y0-$2)<Delta) & (abs(z0-$3)<Delta) ? 1 : 0):(1) smooth frequency
    unset table
    # extract the number from $Occurrences which will be used to color the datapoint
    set table $Dummmy
        plot $Occurrences u (c0=$2,0):($0) every ::1::1 with table
    unset table
    ColC[i] = c0
}

# put the arrays into a dataset again
set print $Data
do for [i=1:RowCount] {
    print sprintf("%g\t%g\t%g\t%g",ColX[i],ColY[i],ColZ[i],ColC[i])
}
set print

TimeEnd = time(0.0)
print sprintf("Duration: %.3f sec",TimeEnd-TimeStart)

set palette rgb 33,13,10
splot $Data u 1:2:3:4 w p ps 1 pt 7 lc palette z notitle

set terminal gif animate delay 30
set output "Density.gif"
Amin = 40
Amax = 60
AFrames = 25
do for [i=0:AFrames] {
    print sprintf("Frame %g, Angle: %.1f", i, sin(2*pi*i/AFrames)*(Amax-Amin)+Amin)
    set view 45,(sin(2*pi*i/AFrames)*(Amax-Amin)+Amin)
    replot
}
set output

should result in:

How to plot (x,y,z) points showing their density

1 Answers