ID Land Surveyor flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Linear misclosure

The straight-line distance between the computed endpoint and the starting point of a closed traverse, found as the square root of the sum of squared latitude and departure misclosures.

Relative precision

Linear misclosure divided by total traverse perimeter, expressed as a fraction 1:N. A smaller misclosure relative to perimeter means higher precision.

Compass rule

A traverse adjustment that distributes latitude and departure misclosures in proportion to each course length, so longer legs receive larger corrections. Also called the Bowditch rule.

Transit rule

A traverse adjustment distributing misclosure in proportion to the magnitude of each latitude or departure rather than leg length, used when angles are more reliable than distances.

Latitude and departure

Latitude is the northing change of a course, distance times the cosine of bearing angle; departure is the easting change, distance times the sine. Sums close to zero in a closed traverse.

Double meridian distance

Twice the distance from a traverse vertex to the reference meridian, used to compute area as the sum of DMD times latitude. First leg DMD equals its departure.

Coordinate area formula

The shoelace method: twice the area equals the sum of each X coordinate times the difference of the adjacent Y coordinates, taken in order around the traverse.

Degree of curve

The central angle subtended by a 100-foot arc under the arc definition, related to radius by D = 5729.578/R. Chord definition uses a 100-foot chord instead.

Tangent distance

The straight distance from the point of intersection to the point of curvature or tangency on a horizontal curve, computed as R times the tangent of half the intersection angle.

Middle ordinate

The distance from the midpoint of a horizontal curve to the midpoint of its long chord, equal to R times one minus the cosine of half the intersection angle.

External distance

The distance from the point of intersection to the midpoint of a horizontal curve, equal to R times the secant of half the intersection angle minus R.

Vertical curve K value

Curve length divided by algebraic grade change in percent; a larger K gives a flatter, longer curve and is used to check stopping-sight-distance design criteria.

Vertical curve turning point

The station where grade becomes zero, located at x equals negative g1 times L divided by the grade change, measured from the beginning of the vertical curve.

Leveling arithmetic check

The sum of backsights minus the sum of foresights must equal the final elevation minus the initial elevation, confirming no booking or reduction error occurred.

Curvature and refraction

Combined correction to level rod readings, about 0.0206 times the square of the distance in thousands of feet, subtracted because the line of sight curves downward.

Interior angle closure

The measured sum of interior angles of a closed polygon should equal n minus two times 180 degrees; the difference is the angular misclosure, distributed equally among the angles.

Elevation factor

A reduction factor approximately equal to Earth radius divided by Earth radius plus orthometric height, converting ground distances to the ellipsoid before applying the grid scale factor.

Lambert conformal conic

A map projection using two standard parallels where scale is exact, well suited to zones with a dominant east-west extent; scale is smaller between the parallels.

Transverse Mercator projection

A conformal projection using a central meridian with exact scale, suited to north-south zones. Scale increases with distance east or west of the central meridian.

Standard error of mean

The standard deviation of individual measurements divided by the square root of the number of observations; precision improves with the square root of sample size.

Error propagation sum

For a quantity computed as a sum or difference of independent measurements, the variance equals the sum of the individual variances; standard deviations do not simply add.

Bearing to azimuth

Convert a quadrant bearing by adding or subtracting from 0, 180, or 360 degrees depending on quadrant: NE as is, SE from 180, SW plus 180, NW from 360.

Backsight and foresight

A backsight is a rod reading on a known point after instrument setup; a foresight is a reading on a point whose elevation is being determined.

Height of instrument

The elevation of the level line of sight, equal to the known point elevation plus its backsight reading; foresight readings are subtracted to obtain new elevations.

Horizontal curve length

The arc distance from point of curvature to point of tangency, equal to radius times intersection angle in radians, or 100 times the intersection angle divided by degree of curve.

Point on tangent offset

For staking by offsets, the offset from a tangent to a curve at distance x equals x squared divided by twice the radius for flat curves.

Traverse station angle

A horizontal angle measured at a traverse station between the backsight and foresight; angle condition and side condition together define traverse geometric closure.

Three-point resection

Determining an unknown instrument position from angles to three known points; the position is indeterminate on the circumcircle through those three points.

Datum and benchmark

A datum is the reference surface for elevations, such as the North American Vertical Datum of 1988; a benchmark is a stable monument of known elevation.

Random versus systematic error

Random errors are equally likely positive or negative and average out; systematic errors bias results consistently and cannot be reduced by repetition alone.

Grid versus ground distance

Grid distance equals ground distance multiplied by the elevation factor and the map projection scale factor, placing measured distances on the state plane coordinate grid.

Sight distance on curve

The clear distance along a curve, checked against design speed; on horizontal curves, roadside obstructions are measured by the middle ordinate needed for the sight chord.