Unit 2 Fundamentals of Surveying Flashcards
What is the Science of Surveying
Surveying determines the relative location of points on or near the earth’s surface.
The science of measuring horizontal and vertical distances between objects, measuring angles between lines, determining line direction, and establishing points based on angular and linear measurements.
What are the methods of surveying
Geodetic and Plane
What is Geodetic surveying
Have highest precision and cover large areas. More precise instruments and procedures are required than for plane surveys.
How are positions expressed in Geodetic surveys
Expressed as latitude/longitude or as Northing/Easting
What is latitude
angular distance North or south of the equator
What is longitude
angular distance east or west of prime meridian
What is Plane surveying
Surveys we are most involved with. When extent of survey is smaller than 250 km and limited accuracy is required. Earth is assumed to be flat surface. Calculations are made using geometry and trigonometry. Examples: highway and railroad surveys considered plane surveys
What are the types of surveying?
Optical and GPS
What is Optical surveying
Revolves around the concept of a known position, distance, and direction. Direction is expressed in angular unit of measurement known as a degree. Degrees are broken into minutes, Minutes broken into seconds
What tools are used for optical surveying
Total station and Auto-level
What does Auto-level use to get measurements?
Philly Rod (determines the differences in height between objects
What are typical optical errors?
Calibration, Parallax, Refraction, Prism offset, human error. Most common is human error
What is parallax?
When instrument is not properly adjusted, resulting in a poor sighting of objects
What is refraction?
bending of light rays which causes poor sighting or poor survey shots. Prevent by avoiding excessively long shots
What is prism offset
All prisms have an offset regardless of how small, impossible for prism to sit directly over top of a point and provide 360 degree coverage
What are common human errors
Fat fingering buttons/numbers, improper notes, not setting up job correctly
Describe GPS Surveying
A passive, all weather, 24 hour Global Navigational Satellite System (GNSS) operated and maintained by the DOD. Consists of no less than 24 satellites in orbit. Ground based static or roving GPS receiver is a range measurement device. Distances measured between receiver antenna and four or more satellites in view, position determined from the adjusted intersections of the signals.
What are the three segments of GPS
space segment, control, user segment
What does space segment of GPS Surveying consist of?
Designed with four satellites in each of six orbital planes inclined at 55 degrees to the equator. Number of satellites varies on time of day and their locations. Satellites are 20,200 km altitude and have 11 hour 58 min orbital periods.
What space satellite systems are available?
GNSS (USA), GLONASS (Russia), GALILEO (Europe), CNSS (China)
Describe the Control Segment of GPS surveying
Consists of Master Control Station and six monitoring stations located throughout the world. Master Control Station located in Schriever AFB, CO. Backup station is located in Vandenburg AFB, CA. Info from monitoring stations that track satellites is used in controlling the satellites and predicting their orbits. All data from tracking stations are transmitted to Master Control Station. Ephemerides, clock corrections, and other message data are then transmitted back to monitoring stations. Ephemeris data used to calculate precisely where the satellite was at the start of message. GPS almanac is also transmitted which includes health of entire GPS satellite constellation.
Describe User Segment of GPS Surveying
Represents the ground based GPS receiver units that process the GPS satellite signals and compute the position and/or velocity of the user.
What are typical GPS Errors?
Multipath, Position dilution of Precision (PDOP), Atmospheric effects, Human Error
What is multipath
when GPS signal (ephemeris) is reflects off a hard object such as building or car. Causing error due to signal not following direct path
What is PDOP
when satellites are all clustered in one location in the sky. Causes poor triangulation
What are Atmospheric Effects
Can delay and distort the ephemeris (GPS Signal). Ionosphere contains many electrically charged particles that causes GPS signal to be reflected. Troposphere holds water molecules which causes signal to be reflected
What are GPS human errors
Fat fingering, inputting wrong data, not taking enough observations to calculate accurate point
What is a datum
Point of origin
What are the two types of datums
local and geocentric
What is local datum
Reference point that is situated on the earth surface with the ellipsoid or geoid being referenced around that. Local datums are more accurate
What is Geocentric Datum
Reference point is the center mass of Earth
What horizontal datum does the US use?
NAD 83
What vertical datum does the US use?
NAVD 88
What datum is tied to GPS and used by DOD and defined by NGA
WGS 84
What is a geoid model
Accounts for the differences between the ellipsoid shape and the actual shape of the earth. Geoid is defined as the hypothetical shape of the Earth’s surface at mean sea level. It is perpendicular to the direction of gravity pull
What is ellipsoid
Also known as spheroid. Ellipsoid has a center, or datum, to which the ellipsoid is referenced from. Geoid is irregular shape which makes calculating distances/angles difficult. SMWs created work around using mathematical shape to best represent the shape of earth using an ellipsoid.
What are Coordinate Grid Systems (GCS)
Uses 3-D spherical surface to define locations on the earth. Datums are part of a GCS. GCS includes angular unit of measure, a prime meridian, and a datum. Lat and Long are considered a GCS.
What is projected coordinate system
Defined on a flat, 2-D surface. Has constant lengths, angles, and areas across the two dimensions. Always based on a GCS that is sphere or spheroid
What is Universal Transverse Mercator Coordinate system?
UTM is a projected coordinate system using Cartesian coordinates. Divides the earth into 60 zones by longitude (vertical) lines. Each zone has its own Cartesian coordinate system independent of other zones. UTM is military’s primary coordinate system.
What is MGRS?
Grid reference system based upon the UTM coordinate system and its zones. Used by NATO to reference earth.
What is Continuously Operating Reference Systems (CORS)?
Used to correct data for GPS surveys. Comprised of several sub networks operated by more than 200 organizations
Define accuracy per surveys
closeness of a measured value to a standard or known value
Define precision per survey
closeness of two or more measurements to each other
What is order of accuracy
Specifications are based on the minimum degree of accuracy allowed for a particular survey, and the range between the allowed degrees is called the order of accuracy. Measurements for first order accuracy surveys are most accurate. Construction surveys require a minimum 3rd order of accuracy
Describe high order surveys
Surveys requiring accuracies of First Order (1:100,000) or better should be performed using FGDC geodetic standards and specifications. These Surveys must be adjusted or evaluated by NGS if official certification relative to the national network is required.
