Particle tracking using IDL
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mkpov.pro

This routine helps you make 3D pictures from your data, using the public domain 3D rendering routine POV-Ray. See also:

Introduction/IDL routines (you are here)
Stepping through a POV-Ray file
Running POV-Ray on a Linux computer
Running POV-Ray on a Windows computer

POV-Ray is a standalone program that runs on a variety of operating systems. The mkpov routine generates a text file that is interpreted by POV-Ray to produce a picture. mkpov has a variety of options to help you make a nice picture. POV-Ray is a powerful program and can make beautiful and realistic pictures. Having it simply draw spheres is vast overkill, but it works. Furthermore, it makes it easy to change the color & size of each sphere individually.

Basic syntax:
IDL> pts=fltarr(3,1000)
IDL> t=findgen(1000)/1000*3.14159*2*30
IDL> pts(0,*)=10*cos(t/3)
IDL> pts(1,*)=10*sin(t/5)
IDL> pts(2,*)=10*sin(t/2)
IDL> mkpov,pts,'img01.pov'
center of data at: 11.0000 11.0000 30.0000 camera at: 11.0000 11.0000 64.0000
IDL> $x-povray +Iimg01.pov +D 2>err

The mkpov command creates the file "img01.pov". The last command calls the linux routine x-povray which generates the picture. This is a three-dimensional Lissajous figure. Larger values of x are at the left of the picture. Larger values of y are at the top of the picture. Larger values of z are closer to you.

mkpov keywords: (Brief listing here, see examples below)

/NOBOX: Don't draw the blue box around the points.
MARGIN = 0: The default, when drawing the box, is to have it closely fitted to the data. Use the MARGIN keyword to extend the box in all directions. For example, MARGIN=2 makes the box extend spatially by 2 units in each direction; see below.
COLOR: Use to pass color information about each sphere; see below.
RADIUS: Use to set the radius of each sphere. If this is a scalar, then the same radius is used for each particle. If this is a vector, then each particle can have its own radius; see below.
CAMERA = [x,y,z]: Control the position of the POV-Ray "camera". The default tries to pick something reasonable, but occasionally gets it wrong. mkpov prints out the default camera location if the CAMERA keyword isn't used, as shown in the example above.
LOOKAT = [x,y,z]: Controls where the POV-Ray camera looks at. The default is the center of the data, which is printed out each time mkpov is called, as shown in the example above. Sometimes you want to compare different data sets with slightly different centers, so it can help to fix the camera position & "lookat" to be the same for the different data sets, rather than taking the defaults.
/BW: force picture to be in black & white. Is overridden if you use the COLOR keyword (in which case only the box is done in grey scale).

More examples:

	Using color: Starting with the array pts defined in the first example: IDL> col=fltarr(3,1000) IDL> col(0,)=findgen(1000)/10000.6+0.2 IDL> col(1,)=col(0,) IDL> col(2,)=col(0,) IDL> mkpov,pts,'img02.pov',color=col,/nobox IDL> $x-povray +Iimg02.pov +D 2>err Here I've made an array col which is in one-to-one correspondence with the data array (pts). I've filled it with greyscale values between 0 and 1, or in this case, actually between 0.2 and 0.8. Also, I've used the /nobox keyword to turn off the bounding box.
	To be more colorful: IDL> col=bw2rgb(t) IDL> mkpov,pts,'img03.pov',color=col,/nobox IDL> $x-povray +Iimg03.pov +D 2>err Now I'm using the program bw2rgb which converts an array of greyscale values into red/green/blue values. (Here, my greyscale array is the original t array defined in the first example at the top of this page.)
	Different coloring: IDL> col=bw2rgb2(t) IDL> mkpov,pts,'img04.pov',color=col,/nobox IDL> $x-povray +Iimg04.pov +D 2>err bw2rgb2 has slightly more intense colors.
	Different coloring: IDL> col=bw2hotcold(t) IDL> mkpov,pts,'img05.pov',color=col,/nobox IDL> $x-povray +Iimg05.pov +D 2>err bw2hotcold maps 0 to blue, 1 to red.
	Changing particle size: IDL> rad=(sin(t/6)+1.5)0.4 IDL> mkpov,pts,'img06.pov',radius=rad,/nobox IDL> $x-povray +Iimg06.pov +D 2>err Here I've defined the array rad* which specifies the radius of each particle. The units for radius are the same as the input data.
	Changing camera angle: IDL> col=bw2rgb2(t) IDL> mkpov,pts,'img07.pov',color=col,/nobox,camera=[34,11,54] IDL> $x-povray +Iimg07.pov +D 2>err I've moved the camera to a larger x value and slightly smaller z value. This is sort of like rotating the image to the right. See also the next example.
	Changing the box margin: IDL> mkpov,pts,'img08.pov',color=col,camera=[34,11,70],margin=2 IDL> $x-povray +Iimg08.pov +D 2>err I've moved the camera again, further away and closer to the original angle; and also added a margin of 2 units to the box size.
	Slightly different camera angle: IDL> mkpov,pts,'img09.pov',color=col,camera=[11,34,70],margin=2 IDL> $x-povray +Iimg09.pov +D 2>err I've moved the camera again.

Extras

More info:

Stepping through a POV-Ray file. This page describes what each line of the POV file is doing, so that if you want to further enhance your pictures, you know where to start. It uses img01.pov as an example file (which corresponds to the very first picture on this webpage).
Running POV-Ray from Linux -- my very brief tutorial
POV-Ray home page
Programs:
download all in a zip file
POV-Ray input files from examples above:
img01.pov
img02.pov
img03.pov
img04.pov
img05.pov
img06.pov
img07.pov
img08.pov
img09.pov

Contact us

Eric Weeks: weeks(at)physics.emory.edu (He wrote this page, and mkpov.)