Horizontal and Vertical Geodetic Control Data for the Unites States.

The National Geodetic Survey produces geodetic data. Geodetic data comprise the results of geodetic surveys to determine, among other things, latitude, longitude, height, scale, and orientation control. The National Geodetic Survey original field survey project observations and final reports are accessioned into records system of the National Archives and Records Administration of the U.S.A. These surveys provide information valuable for a variety of uses in the mapping, charting and surveying community. The NGS' final product is the geodetic data sheet. Geodetic data sheets are comprehensive summaries of all published information for a given geodetic reference point, including: the geographic position and/or height based on the current reference datum, condition of the survey mark when it was last visited, a description of where the point is located and how to reach it, and an explanation of the terms used in the data sheet. In support of these geodetic data, the NGS provides software, publications, and various user services, including geodetic advisor program, instrument calibration, surveying standards, and technical workshops. This dataset contains certain information extracted from the above mentioned data sheet.

The geodetic data must be submitted in the digital formats specified in the FGCS (formally FGCC) publication "Input Formats and Specifications of the National Geodetic Survey Data Base" which describes the formats and procedures for submission of data for adjustment and assimilation into the National Geodetic Survey Data Base. Separate volumes of this publication refer to horizontal (volume 1), vertical (volume 2), and gravity (volume 3) control, and are available from NOAA, National Geodetic Survey, 1315 East-West Hwy, Code N/CGS1, Silver Spring, MD, 20910 (1-301-713-3242). Note guidelines for submission of three-dimensional Global Positioning System (GPS) relative positioning data are contained in annex L to volume 1.

The current attributes and their meaning are shown below.

#FeatureId
Temporary unique ID assigned to this station.

DATA_DATE-
The date when this information was retrieved from the NGS database.

DATA_SRCE-
Data Source where the information for the mark came from.
You should use this link to obtain a full datasheet for the mark
or obtain the datasheets from http://www.ngs.noaa.gov/cgi-bin/datasheet.prl
if you intend to use the data for survey control.

DEC_LONG-
Decimal equivalent of the LONGITUDE
Always displayed to 10 decimal places, but you should
see POS_SRCE and POS_ORDER to determine the true accuracy.

DEC_LAT-
Decimal equivalent of the LATITUDE

PID-
Permanent Identifier assigned by NGS to each mark

NAME-
Station Name (a.k.a. Designation)

STATE-
State Code

COUNTY-
County Name

QUAD-
USGS Topographic Quad Map Name

LATITUDE-
Latitude in Deg-Min-Sec format

LONGITUDE-
Longitude in Deg-Min-Sec format

POS_DATUM-
Datum of the LATITUDE,LONGITUDE
Should always be NAD83

DATUM_TAG-
Datum Tag of the LATITUDE,LONGITUDE
NAD83 (1986) indicates positions on the NAD83 datum for the
North American Adjustment, completed in 1986.
NAD83 (nnnn) indicates positions on the NAD83 datum for the
North American Adjustment, but readjusted to a State High
Accuracy Reference Network (HARN) on the date shown in (nnnn).
NAD83 (CORS) indicates positions which are part of the CORS
network.

POS_SRCE-
Position Source for the LATITUDE,LONGITUDE

ADJUSTED = Least squares adjustment.
(Lat,Lon Rounded to 5 decimal places.)

HD_HELD1 = Differentially corrected hand held GPS observations.
(Lat,Lon Rounded to 2 decimal places.)

HD_HELD2 = Autonomous hand held GPS observations.
(Lat,Lon Rounded to 1 decimal places.)

SCALED   = Scaled from a topographic map.
(Lat,Lon Rounded to 0 decimal places.)

ORTHO_HT-
Present if available.
The Orthometric Height in METERS indicating the height above the Geoid.

VERT_DATUM-
Datum of the ORTHO_HT

VERT_SRCE-
Vertical Source for the ORTHO_HT

ADJUSTED = Direct Digital Output from Least Squares Adjustment
of Precise Leveling.
(Rounded to 3 decimal places.)

ADJ UNCH = Manually Entered (and NOT verified) Output of
Least Squares Adjustment of Precise Leveling.
(Rounded to 3 decimal places.)

POSTED   = Pre-1991 Precise Leveling Adjusted to
the NAVD 88 Network After Completion of
the NAVD 88 General Adjustment of 1991.
(Rounded to 3 decimal places.)

READJUST = Precise Leveling Readjusted as Required
by Crustal Motion or Other Cause.
(Rounded to 2 decimal places.)

N HEIGHT = Computed from Precise Leveling Connected
at Only One Published Bench Mark.
(Rounded to 2 decimal places.)

RESET    = Reset Computation of Precise Leveling.
(Rounded to 2 decimal places.)

COMPUTED = Computed from Precise Leveling Using
Non-rigorous Adjustment Technique.
(Rounded to 2 decimal places.)

LEVELING = Precise Leveling Performed by Horizontal
Field Party.
(Rounded to 2 decimal places.)

H LEVEL  = Level between control points not connected
to bench mark.
(Rounded to 1 decimal places.)

GPS OBS  = Computed from GPS Observations.
(Rounded to 1 decimal places.)

VERT ANG = Computed from Vertical Angle Observations.
(Rounded to 1 decimal place;
If No Check, to 0 decimal places.)

SCALED   = Scaled from a Topographic Map.
(Rounded to 0 decimal places.)

U HEIGHT = Unvalidated height from precise leveling
connected at only one NSRS point.
(Rounded to 2 decimal places.)

VERTCON  = The NAVD 88 height was computed by applying the
VERTCON shift value to the NGVD 29 height.
(Rounded to 0 decimal places.)

ELLIP_HT-
Present if available.
The ellipsoid height in METERS referenced to GRS80 ellipsoid.

POS_ORDER-
Order of accuracy for the LATITUDE,LONGITUDE
Should be one of the following-
A,B,1,2,3

Order and class for Orders 1, 2, and 3
are defined in the Federal Geodetic Control Committee publication
"Standards and Specifications for Geodetic Control Networks".

In addition-
Order A stations have a relative accuracy of
5 mm +/- 1-10,000,000 relative to other A-order stations.

Order B stations have a relative accuracy of
8 mm +/- 1- 1,000,000 relative to other A- and B-order stations.

VERT_ORDER-
Order of accuracy for the ORTHO_HT
Should be 1,2, or 3 for Vertical Control Stations.
Will be blank for stations used for Horizontal Control only.

Also see attribute DIST_RATE which is used for some
vertical control stations.

Vertical order and class for 1, 2, and 3
are defined in the Federal Geodetic Control
Committee publication "Standards and Specifications for Geodetic
Control Networks".  In addition-

Vertical control which were determined only for the purpose of
supplying a height for Horizontal Distance Reductions are
assigned an order of 3.

Class 0 is used for special cases of
orthometric vertical control as follows-

Vertical Order/Class               Tolerance Factor
--------------------               ----------------
1    class 0                   2.0 mm or less
2    class 0                   8.4 mm or less
3    class 0                  12.0 mm or less

VERT_CLASS-
Should be 0, 1, or 2
See details under ELEV_ORDER

DIST_RATE-
Distribution rate for POSTED and READJUSTED benchmarks
which do not have an Order and Class are as follows
"Posted bench marks" are vertical control points in the NGS data
base which were excluded from the NAVD 88 general adjustment.
Some of the bench marks were excluded due to large adjustment
residuals, possibly caused by vertical movement of the bench marks
during the time interval between different leveling epochs.
Adjusted NAVD 88 are computed for posted bench marks by
supplemental adjustments.

A range of mean distribution rate corrections is listed for each
posted bench mark in the data portion of the publication.
A summary table of the mean distribution rates and their codes is
listed below.  The mean distribution rate corrections which were
applied to the original leveling observations is a good
indication of the usefulness of the posted bench marks' adjusted
NAVD 88 heights.

Distribution                     Distribution
Rate Code                      Rate Correction
------------                    ---------------
"a"                        0.0 thru 1.0 mm/km
"b"                        1.1 thru 2.0   "
"c"                        2.1 thru 3.0   "
"d"                        3.1 thru 4.0   "
"e"                        4.1 thru 8.0   "
"f"                        greater than 8.0 mm/km

POSTED BENCH MARKS SHOULD BE USED WITH CAUTION.  As is the case for
all leveling projects, the mandatory FGCS check leveling two-mark or
three-mark tie procedure will usually detect any isolated movement
(or other problem) at an individual bench mark.  Of course, regional
movement affecting all the marks equally is not detected by the two-
or three-mark tie procedure.

FIRST_RECV-
Date when the station was first monumented
or in the case of landmarks, first observed.

LAST_RECV-
Date when the station was last recovered.

LAST_COND-
Last recovered condition of the mark.
Should be one of the following-
MONUMENTED
FIRST OBSERVED
GOOD
POOR
MARK NOT FOUND
SEE DESCRIPTION
DESTROYED

LAST_RECBY-
Agency who reported the last condition of the mark.

STABILITY-
The stability of the mark may have 1 of 4 codes as indicated below-
A = MOST RELIABLE AND EXPECTED TO HOLD POSITION/ELEVATION WELL
B = PROBABLY HOLD POSITION/ELEVATION WELL
C = MAY HOLD, BUT OF TYPE COMMONLY SUBJECT TO SURFACE MOTION
- E.G. FROST HEAVE, ETC
D = MARK OF QUESTIONABLE OR UNKNOWN STABILITY

HT_MOD-
Designates if this site is a Height Modernization site. Y - Yes.

CORS_ID-
Continuously Operating Reference Stations (CORS) site ID.

PACS_SACS-
Designates whether this is a Primary Airport Control
Station (PACS) or Secondary Airport Control Station (SACS).

GEOID_HT-
Present if available.  The geoid height in METERS referenced
to the geoid model attribute.

N_ACC_HZ-
Horizontal network accuracy at the 95 percent confidence level (cm).

N_ACC_EL-
Ellipsoid height network accuracy at the 95 percent confidence level (cm).

N_ACC_STD_N-
North component of coordinate standard deviation (latitude), used to compute horizontal network accuracy (cm).

N_ACC_STD_E-
East component of coordinate standard deviation (longitude), used to compute horizontal network accuracy (cm).

N_ACC_STD_H-
Up component of coordinate standard deviation (ellipsoid height), used to compute ellipsoid height network accuracy (cm).

N_ACC_CORR-
Correlation coefficient between north and east components of coordinate standard deviation (latitude and longitude), used to compute horizontal network accuracy (unitless).

ECEF_X-
The computed Earth-Centered, Earth-Fixed X position.

ECEF_Y-
The computed Earth-Centered, Earth-Fixed Y position.

ECEF_Z-
The computed Earth-Centered, Earth-Fixed Z position.

SPC_ZONE-
The State Plane Coordinate Zone.

SPC_NORTH-
The State Plane Coordinate Northing.

SPC_EAST-
The State Plane Coordinate Easting.

SPC_CONV-
The State Plane Coordinate Convergence Angle.

SPC_CSF-
The State Plane Coordinate Combined Scale Factor.

UTM_ZONE-
The Universal Transverse Mercator Zone.

UTM_NORTH-
The Universal Transverse Mercator Northing.

UTM_EAST-
The Universal Transverse Mercator Easting.

UTM_CONV-
The Universal Transverse Mercator Convergence Angle.

UTM_CSF-
The Universal Transverse Mercator Combined Scale Factor.

DYNAMIC_HT-
The computed dynamic height at a bench mark using the
orthometric height referenced the NAVD 88 and a gravity value.

MODELEDGRAV-
The interpolated gravity value which was used in the
NAVD 88 general adjustment.

MARKER-
Identifies the type of marker.

SETTING-
Identifies the type of setting.

STAMPING-
Identifies the stamping on the disk.

All values were obtained from the NGA Datasheet
available at <http://www.ngs.noaa.gov/cgi-bin/datasheet.prl>