Practical Crime Scene Ch. 7
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26 terms
Terms | Definitions |
|---|---|
 The five basic elements of a sketch are: | Heading, Diagram area, Legend, Title block, and Scale and direction notations |
| Heading is a | nation that indicates why the sketch was created (i.e. sketch depicting evidence and measurements or bullet trajectories) |
| Diagram area is the | drawing itself |
| The legend tells viewer | what the various labels used in the diagram depict |
| The title block of the sketch provides | important information relevant to the location of the scene and the creator of the sketch |
| The two annotations, scale and direction, should be present | on the sketch to identify the orientation of the sketch to compass direction as well as to inform the viewer id there is scale of reference |
| It is neither practical nor advisable in all in all situations to create a sketch with north facing the top of the page. | Rather set the diagram area in the most effective orientation to depict the scene and then simply identify where north is in relation to this orientation. |
| The typical crime scene sketch is that of a bird's eye view but there are several variations of the view for the crime scene sketch. These are: | Cross projection or exploded sketch, Elevation sketch, Three-dimensional sketch or view |
| Cross projection or exploded sketch combines the | standard bird's-eye view of the horizontal surface of the room while at the same time "laying down" a wall or walls in order to depict evidence that is present on these vertical surfaces. |
| An elevation sketch is drawn depicting | a side view of some portion of the scene typically an interior wall or similar vertical structure |
| The three dimensional sketch or view offers | an ability to present the crime scene information in a more realistic perspective |
| In practice, no matter which mapping method the technician uses | the technician fixes all evidence first. |
| The rectangular coordinates method is best suited for crime scenes with clear and specific boundaries. It is well suited for interior crime scenes. | Evidence is fixed by measuring at right angles from the evidence to the surrounding walls and surfaces. Rectangular coordinates require only two measurements from any item of evidence, but even with measurements. It is effective but not as precise as other techniques. |
| Triangulation is an effective method for fixing evidence. Items that have a regular shape (furniture, guns, or knives) are fixed using a minimum of four measurements. | Irregularly shaped objects (blood pools, clothing) are documented using two measurements from the center of mass of the item to two distinct landmarks, as well as measurement of the overall width of the items. |
| In triangulation, regularly shaped articles end up with two "triangles" (four measurements), | and irregularly shaped objects end up with one triangle (two measurements) |
| The technician should not triangulate | from items that are themselves fixed in the scene by triangulation |
| Baseline coordinates is best suited for exterior scenes with evident landmarks, it can also be used inside. | The datum point is set by triangulating it to a set of nearby landmarks and then the baseline is extended along a cardinal direction as far as necessary. Measurements are taken from the evidence at a right angle to the baseline. |
| Polar coordinates are based on surveying techniques. Using a sighting device, the technician measures two to three basic measurements from a known point to the evidence in question. These three measurements are the | horizontal angle, the horizontal distance the difference in elevation |
| Horizontal angle, a measurement of 1 to 360 degrees, is measured | as rotation of the sighting instrument from north in the horizontal plane. |
| Horizontal distance is measured as the distance between | the datum point and the evidence item. |
| Elevation is measured as the difference in height from | a benchmark (the datum point evaluation) and the evidence. |
| Two additional steps must be accomplished before recording elevation. | #1 The height of the instrument above the datum point. This distance is subtracted from the elevation reading to establish the actual elevation. (Vertical scale measurement minus the instrument height equals evidence elevation relative to the datum point). |
| Two additional steps must be accomplished before recording elevation. | #2 The technician must properly place the sighting device at a higher elevation htan any evidence items. |
| Datum point can be set by use of a GPS, triangulation to evident landmarks, or by | placing a metal pipe or rebar on the ground. The datum point should be placed in a position from which the majority of known evidence items an be seen. |
| Total-station mapping are automated surveying systems that | uses methods similar to polar coordinates. |
| Once properly leveled in the scene, alignment of the total station to magnetic north is | unnecessary because of the accuracy of the total station. |
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