You have requested a report of controlling monuments that Nevada Department of Transportation (NDOT) has surveyed or tied in the past. It is our intent to explain the data, its meaning and our expected positional tolerances of the monument position. Perhaps the most critical element in this report may be the physical monument description at a given point in time. A thorough review of the data presented in this report will assist laymen or professionals in the completion of their duties or tasks. Further we hope to perpetuate the location of monuments by making this information accessible to all. Please note that we are documenting positions of monuments and not necessarily corners. They may be one and the same or not and that is the responsibility of the trained professional to make that judgment. We welcome you to use this data to facilitate your project, but first our disclaimer:
This geodetic data was developed for use by the Nevada Department of Transportation (NDOT) under controlled conditions of software maintenance, input quality, processing configurations and output data utilization. Any use of this data by other than NDOT would be under conditions not necessarily subject to such controls. Therefore, NDOT makes no warranties, expressed or implied, concerning the accuracy, completeness, reliability, or suitability for any particular purpose of the data furnished.
NDOT does include a brief description of monuments to assist in the evaluations of said monument locations but makes no claim to their absolute authenticity.
Comments or concerns may be directed to:
Station: This is the name of the geodetic corner and
is unique to that point. It may be NGS's name or NDOT's assigned name but should
never be duplicated if the physical description of the monument remains unchanged.
A full explanation of NDOT's naming convention is given in the Consultant Handbook
for Survey and Mapping. The letter appended to the end of each name is a monument
type indicator.
Geodetic/N: Position measured from the Equator (latitude)
using the shape of the Earth as defined by a given geodetic datum. North is positive.
Geodetic/E: Position measured from Greenwich (longitude)
using the shape of the Earth as defined by a given geodetic datum. East is positive.
UTM-11/N: UTM zone 11 northing coordinates typically
used in NDOT's GIS if horizontal datum is NAD83/94.
UTM-11/E: UTM zone 11 easting coordinates typically used
in NDOT's GIS if horizontal datum is NAD83/94
State Plane/N: True state plane Northing (Y) coordinates.
State Plane/E: True state plane Easting (X) coordinates.
kf: Grid scale factor at a given point on the ellipsoid
of the earth used to obtain grid distances from ellipsoid distances and reflect
the linear distribution occurring during that process. Grid scale factors are variable
from point to point and are dependent upon the distance east and west of a zone
central meridian. The ratio of grid distance to the ellipsoid distance.
hf: Elevation scale factor at a given point on the ellipsoid
of the earth used to obtain Ellipsoid distances from observed distances (ground).
NAD 27 sea level distances and ellipsoid distances have traditionally been considered
the same. Elevation scale factors are variable from point to point and are dependent
upon elevations and geoid height separations. The ratio of ellipsoid distance to
the ground distance. NDOT uses a mean radius of Nevada of 6373000 meters in their
calculations.
Ground: Northing and Easting coordinates are modified
state plane coordinates. They are modified in the sense of having an Area Factor
applied to state plane coordinates thus reflecting more precise ground distances
with State Plane bearings. These coordinates are used to design and construct with,
and are the coordinate values used in Design and Right-of-Way Divisions. Ground
Coordinates x Area Factor = State Plane coordinates
Ortho Elevation: The geometrical distance between
the geoid (MSL) and a point on the surface of the earth. Because the geoid is gravity
based or at least everywhere normal to gravity, water seems to flow down hill. NDOT
Vertical datum's used are NGVD29 and NAVD88.
Ellipsoid Elevation: Ellipsoid height measured
from the ellipsoid of the earth using the shape of the Earth as defined by a given
geodetic datum and a modeled geoid.
This number is calculated using the difference model (Geoid ht) and the orthometric
elevation. Because of the uncertainty in the geoid model the ellipsoid elevation
also has a uncertainty (see Geoid Ht).
Geoid Ht: This is the amount of the Geoid-Ellipsoid
separation and is negative in Nevada.
Ortho Elevation = Ellipsoid elevation - Geoid Ht
Ortho Elevation + Geoid Ht = Ellipsoid Elevation
Geoid Hts are determined using a model and as such there is an uncertainty with this number. Rule of thumb is that geoid ht separations determined prior to 2004 have an uncertainty approximating .1 meter. After 2004and using model geoid 2003 that uncertainty is about .05m. Again, the uncertainty in the model is reflected in the listed NDOT ellipsoid Ht.
Convergence: The difference between state plane grid north
and geodetic true north. Commonly referred to as the map angle at NDOT.
Grid Azimuth = Geodetic Azimuth - Convergence angle
sf: Point Combination grid factor is the product of kf and
hf and is used to obtain grid distances from observed ground distances at a given
point. Combined grid factors are variable from point to point and are dependent
upon the elevations and distance from the zone central meridian.
Area cf: This is a combination grid factor developed
for a specific area of survey interest or Location project. Division of grid distances
by this factor results in a near true ground distances at a ratio usually exceeding
1:20000. Mountainous terrain occasionally makes this ratio difficult to achieve.
NDOT does not subtract given amounts from the resulting ground coordinate system.
All surveys at NDOT are adjusted on the grid before conversion to ground.
V Datum: This identifies the vertical reference frame used for a given Project. Navd88 and Ngvd29 are the names of the orthometric NGS vertical datum's commonly in use in Nevada and by NDOT and are commonly based upon mean sea level.
H Datum: This identifies the geodetic reference frame
used such as NAD83,(GRS80) and also epoch date of the adjustment. An example would
be NAD83/94. The 1929 datum does not have an epoch date associated with it.
Zone: The zone where the monument is located as defined
by the Nevada Coordinate System (SP) in Nevada. They are East, Central or West and
are further defined by which county they are in. Each Zone has a specific origin
with unique beginning coordinates values assigned at that geographic location as
defined in NRS327. Occasionally we may also use UTM-11 as defined by NGS.
Units: This reflects the units of the Ground coordinates.
They may be in meters or US Survey feet. Meters x 39.37/12 = US Survey feet.
Date: This date reflects the mean date when the actual
field data measurements occurred.
LPN: This is the Location Project Number assigned to a
specific geographic project or can be thought of as specific data set. Further this
number is the first 3 or 4 numbers of a stamped monument name, using the standard
NDOT naming convention, when setting NDOT monuments.
H-Acc: This is a quality indicator of the horizontal positional
tolerance at 95% confidence in meters. As an example: H-Acc = .02
H-Rel: This is an indicator of how horizontal positions were acquired and of the confidence of the acquisition. Acquisition methods are GPS, Conventional Surveying and Quad scaled. Acquisition confidence indicators are Adjusted, Checked and Unchecked. Options available would then be GA, GC, GU, CA, CC, CU, QA, QC and QU and are determined from the network solution and are the result of the procedures of the survey performed.
| GA = | GPS Adjusted |
| GC = | GPS Checked |
| GU = | GPS Unchecked |
| CA = | Conventional Adjusted |
| CC = | Conventional Checked |
| CU = | Conventional Unchecked |
| QA = | Quad Scaled Adjusted |
| QC = | Quad Scaled Checked |
| QU = | Quad Scaled Unchecked |
V-Acc: This is a quality indicator of the vertical positional
tolerance at 95% confidence in meters. As an example; V-Acc = .005
V-Rel: Vertical acquisition methods at NDOT are GPS, VA(Vertical Angle) or SL(Spirit Level). Confidence levels are indicated by the methods used in the acquisition method and reflect those confidences that have been traditionally indicated over time. This order of confidence is SL, GPS and lastly VA. As a note Spirit Levels are run with precise procedures (3-wire) and exceed 3rd order Class 1 NGS requirements.
Description: The physical description of a monument written by the survey crew at the time of occupation.