Cross section in BRL-CAD

Making a cross-sectional view of a model in BRL-CAD is very easy and fun. All we have to know is just “rt” command and some of its arguments. Following are quick steps to create cross-section of a model:

  1. Open MGED and create / draw model.
  2. Use command saveview fileName  to save the current view of model in a file(shell script).
  3. Run the file generated in step 2 with rt command as:
    sh fileName -s1024 -k 0,-5,0,2000
  4. Step 3 create image in raw format i.e. pix format.
  5. Convert pix image to png as:
    pix-png -s1024 < fileName.pix > fileName.png

The option ‘k’ of “rt” take input as: xdir, ydir, zdir, distance. Here xdir, ydir and zdir define the orientation of cutting plane. The line through Point(xdir, ydir, zdir) is normal to cutting plane. This normal always points away from the space to be subtracted. Since as in 3D geometry, to define a plane we need a normal to that plane. Same is here.

The “distance” is distance of plane from origin. That is, distance specifies position of plane w.r.t. to origin.


We know there are so many users in Ubuntu system other than our sudo account which are not created by us but by system to cater different tasks in the system. Run the command cat /etc/passwd to see all users in the system. One of them is www-data. Whatever you do from browser, it is recorded as work done as www-data. For example, if you create a file from browser, its owner will be www-data. In simple language, browser is www-data user of your system. It is also called Apache user account or webserver account.If you run command, ps -u www-data you will see  number of Apache processes running and their process ids. This command shows all the running processes under a given user. So by checking the processes of the www-data we can conclude that it is Apache’s account. Continue reading www-data