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IDL: Plotting Irregularly-Gridded Data

1. Creating a Dataset
2. The TRIANGULATE Procedure
3. Plotting the Results with TRIGRID

Creating a Dataset

1. Open a window for viewing:

window

2. Set seed to the longword value 1. seed is used to generate random points.

seed=1l

3. Set the number of points to be randomly generated.

n=32

4. Create a set of x values for each of the 32 data points.

x=randomu(seed,n)

5. Create a set of y values for each of the 32 data points.

y=randomu(seed,n)

6. Create a set of z values for each of the 32 data points from the x and y values.

z=exp(-3*((x-0.5)^2+(y-0.5)^2))

7. Plot the XY positions of the random points.

plot,x,y,psym=1,title='Random XY Points'

8. Dismiss the graphics window:

wdelete

The TRIANGULATE Procedure

1. Open a window for viewing:

window

2. To return a triangulation in the variable tr, enter the command:

triangulate,x,y,tr

Note: This is not always a 54-element array, it may vary based on the number of points.

3. To produce a plot of the triangulation, shown below, enter the following commands:

plot,x,y,psym=1,title='Triangulation'
for i=0,n_elements(tr)/3 - 1 $
do begin & t=[tr[*, i],tr[0, i]] & plots,x[t],y[t] & endfor

4. Dismiss the graphics window

wdelete

Plotting the Results with TRIGRID

1. Display a surface plot of the gridded data by passing the result of the TRIGRID function to SURFACE, using the default interpolation technique and add a title to the plot, shown below, by entering:

surface,trigrid(x,y,z,tr)
xyouts,.5,.9,'Linear Interpolation',align=.5,/normal

The TRIGRID function can also return a smoothed interpolation. Set the QUINTIC keyword to use a quintic polynomial method when interpolating the grid.

2. Display the results of the quintic gridding method, shown below, by entering:

surface,trigrid(x,y,z,tr,/quintic)
xyouts, .5,.9,'Quintic Interpolation',align=.5,/normal