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is used to communicate between org.lcsim objects and its HepRep representations. For each type of element you want to display, you will have to create a HepRepType. The name can be the name of the collection in the EventHeader (as is the case in the example) or any string you want. Please make sure it is unique.
We then add some properties to the representation. A complete list of available options and parameters is posted elsewhere.
Finally, for each element in the list of org.lcsim objects (Hep3Vector in this case) we create a HepRepInstance object. It inherits its properties from the HepRepType it belongs to, but you can overwrite the properties. You might, for example want to assign certain colors to different instances, grouping them by momentum, parent, distance, or whatever you can think of. Now that we have created a HepRepInstance, we want to draw it. In order to do that we need to create one (or more) HepRepPoint instances. In this example, where we draw the Hep3Vector as a point, one HepRepPoint is sufficient, but there may be cases where you want to create a more complex representation that requires more points to draw.
Please have a look at the classes in the package org.lcsim.util.heprep for further inspiration.