OR Land Surveyor flashcards

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

Latitude and departure

Latitude equals distance times the cosine of the azimuth; departure equals distance times the sine of the azimuth. For a closed traverse, the sum of each must be zero before adjustment.

Relative precision

Linear misclosure divided by total traverse length, expressed as a ratio such as 1:10,000. It measures the quality of a traverse and is compared to the standard required for the survey class.

Compass rule

A traverse adjustment that distributes the latitude and departure misclosures in proportion to each course length divided by the perimeter. Also called the Bowditch rule.

Azimuth

A direction measured clockwise from north through 360 degrees. A back azimuth differs by 180 degrees: add 180 if the forward azimuth is under 180, subtract otherwise.

Bearing to azimuth

In the northeast quadrant the azimuth equals the bearing. Southeast is 180 minus the bearing, southwest is 180 plus, and northwest is 360 minus the bearing.

Horizontal curve tangent

The tangent distance from the point of intersection to the point of curvature equals the radius times the tangent of half the central angle: T = R tan(Delta/2).

Degree of curve

With the arc definition, the degree of curve equals 5729.578 divided by the radius in feet. With the chord definition, it equals twice the arcsine of 50 divided by the radius.

Vertical curve equation

Elevation equals the BVC elevation plus g1 times x plus (g2 minus g1) divided by twice L, times x squared, where grades are in decimal form and x is distance from the BVC.

Height of instrument

Height of instrument equals benchmark elevation plus backsight. A new point elevation equals height of instrument minus the foresight reading to that point.

Combined factor

Grid distance equals ground distance times the combined factor, which is the map scale factor multiplied by the elevation factor. The elevation factor is approximately R divided by R plus h.

Curvature and refraction

The combined correction is about 0.0206 times the distance in thousands of feet squared, in feet, and is subtracted from the rod reading. It is canceled by balancing backsight and foresight distances.

Area by coordinates

Twice the area equals the sum over all courses of X sub i times Y sub i plus one minus X sub i plus one times Y sub i. Take the absolute value and divide by two.

Double meridian distance

The first course DMD equals its departure. Each later DMD equals the previous DMD plus the previous departure plus the current departure. Double area equals the sum of DMD times latitude.

State plane coordinates

A conformal projection grid using Lambert conformal conic or transverse Mercator. Grid distances differ from ground distances by the combined factor, which must be applied before computing closures.

GNSS minimum satellites

At least four satellites are needed to solve the three position coordinates plus the receiver clock bias. More satellites and lower PDOP values indicate stronger geometry.

RTK fixed solution

A real-time kinematic solution in which the integer carrier-phase ambiguities are resolved. A fixed solution is far more precise than a float solution and is required for control work.

Error ellipse axes

The semi-major and semi-minor axes are the square roots of the eigenvalues of the two-by-two covariance matrix. The ninety-five percent ellipse has about 2.45 times the standard ellipse area.

Standard error of unit weight

A measure of how well the observation weights match the actual scatter of residuals. A value near one indicates consistent weighting; a large value suggests a blunder or wrong weights.

Helmert transformation

A similarity transformation using translations, rotations, and a scale factor. The two-dimensional version has four parameters and needs at least two common control points.

Monument evidence hierarchy

Generally natural monuments control over artificial monuments, which control over adjoining boundaries, then courses and distances, then area. The exact order can vary by state law.

Adverse possession elements

Possession that is actual, open and notorious, exclusive, hostile, and continuous for the statutory period. The specific elements and period are set by state statute.

Accretion versus avulsion

Accretion is gradual and imperceptible change that moves a water boundary and belongs to the riparian owner. Avulsion is sudden and does not change the boundary.

PLSS township layout

A normal township is six miles square with thirty-six sections of one square mile each, numbered from one at the northeast corner and proceeding back and forth across the township.

Aliquot parts description

A description such as the northeast quarter of the southwest quarter of Section 12. The fractions are read from right to left, and the order changes the parcel identified.

Average end area volume

Volume equals the distance between sections times the average of the two end areas. The prismoidal formula adds a middle area term for a more exact result when areas change rapidly.

Cut and fill

Cut equals existing ground elevation minus design elevation, so a positive cut means excavation. Fill is the opposite: design elevation minus existing ground elevation.

Superelevation equation

The relationship among rate of superelevation e, side friction f, speed V in miles per hour, and radius R in feet is e plus f equals V squared divided by fifteen R.

Sight distance on crest curve

Available stopping sight distance depends on the algebraic grade change, the design speed, and the driver eye and object heights. It is checked against the design stopping sight distance.

Two-peg test

A field check that the line of sight of a level is parallel to the bubble tube. It is performed by comparing rod readings over a fixed distance with the instrument set at two positions.

Reciprocal observations

Measuring an angle in both the direct and reverse faces and averaging cancels collimation and vertical index errors. The mean of the two faces is the accepted value.

US survey foot

A legacy unit equal to 1200 divided by 3937 meters, about two parts per million different from the international foot. The difference matters over long distances and in legacy coordinate data.

Resection danger circle

In the three-point problem, if the instrument station and the three known points lie on one circle, the solution is indeterminate. Points near that circle give weak, unreliable results.