Javad TRIUMPH-LS, User Manual

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Coordinate Systems
Geodetic Distance (measured along ellipsoid)
Offsets, Projecting to a Line 1
This application in CoGo>Offsets calculates the distance a
point (P3) is from a line formed by two other points (P1 and
P2). Once solved the user can then store a point (P4) on the
line between P1 and P2 at the perpendicular intersection of
P3>P1-P2. In a geodetic sense, this line could be a geodesic
line or a grid line if a projection is current (such as State
Plane, UTM, etc.). J-Field determines which definition to use
based on the current Coordinate System.
If a geodetic system (latitude and longitude) is current or
a geocentric Cartesian system (ECEF/XYZ) is current, J-Field
uses the geodesic definition of the line P1-P2. If a map
projection; e.g., State Plane, UTM, etc. is used, then
J-Field
uses the grid definition of the line. Over short P1-P2 line
distances, the difference between these two definitions
is minimal; over longer offset distances the difference
becomes more noticeable. J-Field affords the user the
flexibility to choose which definition to use simply by
the selection of the current coordinate system, such that
the results will be consistent with the coordinate system
definition.
Note that this intersection is based on the Grid definition of
the direction of the line from P1 (S104) and P2 (BP1). This is
because a State Plane system was current. Had this system
been geodetic, such as NAD83(2011), the solution would
have been based on the geodesic definition of the direction
from P1 to P2. The distances reported can still be toggled to
reflect the different distance types down line and the offset
from the line regardless of the current coordinate system.