Monday, March 28, 2011

Bushwalking Navigation | A Glossary of Frequently Used Terms

Have you ever wondered what SOG and VMG mean in the context of navigation? What is a breadcrumb trail? What is the difference between a backbearing and a resection? What are waypoints and how do they differ from a  grid reference?
Glossary Terms Description
.kml The KML file specifies a set of features (place marks, images, polygons, 3D models, textual descriptions, etc.) for display in Google Earth, Maps and Mobile, or any other 3D Earth browser (geobrowser) implementing the KML encoding. Each place always has a longitude and a latitude. KML files are very often distributed in KMZ files, which are zipped files with a .kmz extension.
Aiming off Used to find an objective on a feature which is straight eg river, mountain ridge, road.
Deliberately aim to strike the feature 10 ° to right or left of feature and then turn along feature to reach objective (also called
Stefansson method or intentional error)
Attack point A feature, which is near but much easier to find than your objective.
Back Bearing Used to see if you have deviated from the intended path. Face starting point. Check that south end of needle is centred on mark.
Bearing or Course A bearing is the angle between a line connecting two points and a north-south line.
Breadcrumb trail  A track is a compilation of samples or “breadcrumbs” taken over a period of time.
Calibration The process of inputting the grid references of known points, usually the four corners of a map.
Catching feature Prominent features which are beyond your
objective but
can act as safety net. A bearing on prominent feature at
90 ° to direction of travel can be used.
Coordinates In 3D latitude, longitude and elevation
Easting, Northing The terms easting and northing are geographic Cartesian coordinates for a point. Easting refers to the eastward-measured distance (or the x-coordinate), while northing refers to the northward-measured distance (or the y-coordinate). (Wikipedia)
Escape Route These are the routes you will take back to safety if anything prevents your progress to your destination. This could be an injury,
the weather, too slow progress or physical blocking of your route by a landslide, avalanche, bushfire or flooded river.
Grid Reference Numerical grid references consist of an even number of digits. Eastings are given before Northings. Thus in a 6 digit grid reference 123456, the Easting component is 123 and the Northing component is 456. (Wikipedia)
Handrail Definite features which are roughly aligned with direction of travel and which make navigation easier. Don't use creeks or gullies but may run parallel to them.
Heading Compass heading or course measured from true or magnetic north.
Map Datum The horizontal datum is the model used to measure positions on the earth. A specific point on the earth can have substantially
different coordinates, depending on the datum used to make the measurement.
Naismiths Rule A rule of thumb that helps in the planning of a walking or hiking expedition by calculating how long it will take to walk the route including ascents. (Wikipedia)
Pacing A pace is the distance between each right foot hitting ground. For 1.8m person, with
pack, ≈ 1.5m ie 660 paces to 1km.
POI Points of Interest. Often downloaded in advance of a walk.
Raster Map Made up of a grid of pixels also known as bitmap
Resection Used to describe process of drawing three intersecting transect bearings to find your present location. Select features which are at a maximum angle to each other. eg 120 °
Route Two or more waypoints
Route Card The planned route is broken down into a series of legs, each of which begins and ends at a clearly defined feature, and which can be followed on a single compass bearing. In addition, distances, height gains
and losses and times calculated using Naismith’s rule are included.(Wikipedia)
SOG Speed over ground. The speed at which you are moving over the surface of the earth.
Topographic Map A type of map characterized by large-scale detail and quantitative representation of relief, usually using contour lines.
Track A track is a compilation of samples or “breadcrumbs” taken over a period of time. (MotionX GPS)
Transect Bearing Useful to locate exact position on a handrail., by identifying a prominent feature and drawing a back bearing on the map to intersect the handrail.
UTM Universal Transverse Mercator coordinate system; a grid-based method of mapping locations on the surface of the Earth
Vector map Scaleable, small file size, where lines are specified by coordinates not pixels; not raster or bitmap.
VMG Velocity made good. Effective speed at which you are approaching your waypoint.
Waypoint Sets of coordinates which identify a point in space, often given as a grid reference.

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Bushwalking Navigation

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