1. Triangulation Method
The triangulation method uses two fixed points (A and B) to measure the locations of evidence. These fixed points are often permanent structures or markers that are unlikely to move.
Mainly used: Commonly used in indoor crime scenes with well-defined points of reference.
Procedure:
- Measure the distance from point A to the evidence (point x and y).
- Measure the distance from point B to the evidence.
- This creates a triangle, allowing for precise plotting of the evidence on a sketch.
Advantages:
- Highly accurate, especially for indoor scenes or where fixed points are readily available.
- Useful for plotting irregularly shaped areas or multiple items of evidence.
Examples:
- Indoor Crime Scene: In a room where a robbery occurred, fixed points A and B could be the corners of the room. The positions of a broken vase and a dropped wallet are measured from these points, creating a triangle for each piece of evidence.
- Vehicle Collision Scene: At a car crash site, two fixed points can be the positions of lamp posts on the street. The locations of skid marks and vehicle debris are measured from these points.
2. Baseline Method
The baseline method involves establishing a straight line between two fixed points (A and B). Measurements are taken along this line and perpendicular to it to locate evidence.
Mainly Used: Ideal for outdoor crime scenes or where a clear, straight reference line can be established.
Procedure:
- Draw a baseline between two fixed points.
- Measure the distance from point A along the baseline to a point directly perpendicular to the evidence (x).
- Measure the perpendicular distance from the baseline to the evidence (y).
Advantages:
- Simple and quick to use.
- Effective for outdoor scenes or large areas with few fixed points.
Examples:
- Outdoor Crime Scene: At a park where an assault took place, a baseline is established between two trees. The locations of a weapon and a piece of clothing are measured along this baseline and at right angles to it.
- Warehouse Scene: In a large warehouse where theft occurred, a baseline is set between two walls. Evidence such as footprints and dropped items are measured along this baseline.
3. Polar Coordinate Method
The polar coordinate method uses a fixed point and measures the distance and angle from this point to the evidence.
Mainly used: Commonly used in outdoor scenes where establishing a straight baseline is difficult or impractical.
Procedure:
- Establish a fixed point (e.g., Wall A).
- Measure the distance from the fixed point to the evidence (X).
- Measure the angle (e.g., 40° Northeast) using a compass or transit.
Advantages:
- Useful for large or irregularly shaped crime scenes.
- Effective when evidence is scattered over a wide area.
Examples:
- Forest Crime Scene: In a forest where a body is found, a large tree is used as the fixed point. The distance and angle to the body and a nearby piece of clothing are measured from this tree.
- Field Scene: In an open field where a crime occurred, a barn wall serves as the fixed point. Evidence such as a discarded weapon and a set of tire tracks are measured using distances and angles from the barn wall.
4. Rectangular Coordinate Method
The rectangular coordinate system is useful in scenes where there are perpendicular landmarks, such as two walls, two curb lines, and two edges of a building.
- It can be used even with non-perpendicular landmarks if a fixed reference point is chosen (telephone pole, utility box, fire hydrant).
- Measurements taken in cardinal directions (north/east, north/west, south/east, south/west).
- Ideal for indoor scenes or areas with clear, straight boundaries.
- Rectangular coordinate method is less accurate than triangulation method due to potential for perpendicularity errors.
5. Cross-Projection Method
- Cross-Projection Method is useful when the items or locations of interest are on or in the wall surfaces as well as elsewhere in an enclosed space.
- The walls, windows, and doors in a cross-projection sketch are drawn as though the walls had been folded flat on the floor.
- The measurements from a given point on the floor to the wall are then sketched.
Examples
- Hotel Room Murder: In a small hotel room where a body is found, the cross projection method is used. The floor plan shows the bed with the victim, while the unfolded walls display a blood spatter pattern on the north wall, a broken lamp on the east wall, and fingerprints on the door handle on the south wall.