Crime Scene Examination: Polar Coordinate System

Physical and forensic evidence, if properly preserved, collected, maintained, analyzed and reported often is the unimpeachable source of the truth.  Knowing this we also explored the theory of the Locard Exchange Principle and how “every contact leaves a trace” which leads us naturally to the need to properly secure the crime scene to avoid altering it and contaminating the contents of the scene.

One of the methods for crime scene investigation, processing and development that we visited last week was the Cartesian or Rectangular Coordinate System.

The next most popular method and the one most typically used in wide open spaces without clear cut boundaries is the Polar Coordinate System.

Crime Scene Polar Coordinate System
Above pictured is a simple example of a Polar Coordinate System grid where every red mark indicates a uniform interval from the pole

It is a mathematical process whereby we have a central point that is called the pole.  From this central point or pole, we plot out places of interest which are calculated in terms of distance from the pole as well as the angle from the pole in a fixed direction.  This way after the scene is released we have data that is traceable and can be used later to determine where various objects or evidence were relative to one another.

Forensic Science Planimeter
Above pictured is a Planimeter that helps to make a proper Polar Coordinate System model

If we don’t have a mathematical and logical process of preserving, recording and developing a crime scene, then we are reduced to being the functional equivalent of the interested tourist who tramps about and forever alters a scene and contaminates it forever due to the Locard Exchange Principle.

crime scene tourist
"Look honey, isn't that neat? Some blood over there" says the crime scene tourists stepping on top of the shoe prints leading up to the blood
crime scene tourist
"I'm all ready to look for cool stuff at the scene and whatever interests me" says the crime scene tourist
crime scene tourist
"Wow! Lookie here! A bullet hole in the far away wall. I'm going to walk across the carpet to get a quick photo of it for the family album (while I track trace evidence from outside across the scene)" says the crime scene tourist

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