Locations of Boatslips

In this note are my recollections of how I derived and computed the locations of boatslips around Deep Creek Lake.

Determining the locations of the boatslips around the lake was part of my early efforts in working with R and with geospatial data.

This is a collection of unstructured information that got me to convert and make usable in R the coordinates of the boatslips from latitude/longitude coordinates to the Maryland State Plane Coordinate System.

Coordinate Systems

Typical coordinate values for a point I obtained from the County (Deborah Carpenter) and DNR for the shoreline coordinates looked as folllows: 638486.2/679792.4. This a pair of Northerling/Easterling values or UTM coordinates.

These numbers are in MD State Plane Coordinates and reflect the number of ft from a fixed point. That appeares to be the standard way of specifying locations by surveyors in Maryland.

I had done some work in converting the bathymetric data of the lake in a consistent format with some help from Rich Ort of DNR who had recently made all of the bathymetric measurements. I had converted the bathymetric data in lat/lon format via Google Earth/Excel Conversion algorithm that I wrote to get the latitude/longitude coordinates in UTM coordinates.

Throughout I used the following values: esri:102285 is the Maryland State Plane for NAD 83 with units in meters and epsg:4326 as the standard longitude/latitude coordinate system.

Different conversion systems are described in the following references and paraphrased below.

National Geodetic Survey State Plane Coordinate System

The State Plane Coordinate System (SPCS) is not a projection; rather it is a system for specifying positions of geodetic stations using plane rectangular coordinates. This coordinate system that divides all fifty states of the United States, Puerto Rico and the U.S. Virgin Islands into over 120 numbered sections, referred to as zones. Each zone has an assigned code number that defines the projection parameters for the region.

The main aim in creating the SPCS was to design a conformal mapping system for the entire country while maintaining a maximum scale distortion of 1 part in 10,000. In 1933 this was considered the limit of surveying accuracy. In order to attain this accuracy, the larger states needed to be divided into smaller zones or FIPS. Each zone or FIPS has its own central meridian or standard parallels to maintain accuracy.

The original zones were based upon a network of geodetic control points known as the North American Datum of 1927 (NAD27). With improvements within the last 50 years and the need for compatibility with satellite systems, the origin of the datum was moved and NAD83 was created. Hence ZONE refers to the older NAD27 system and FIPSZone to the newer NAD83.

FIPS = Federal Information Processing Standard

The U.S. State Plane Coordinate System

IPS (SPCS ID) 1900 -> EPSG ID 26985 IPS (SPCS ID) 1900 -> EPSG ID 2893 Maryland (ftUS)

Most state plane zones are based on either a transverse Mercator projection or a Lambert conformal conic projection.

MD023(GARRETT CO.) NAD83 ZONE = 1900 (LAMBERT|ONLY A SINGLE ZONE FOR THIS STATE OR COUNTRY)

MARYLAND FIPSZONE: 1900 ADSZONE: 4126 UTM ZONES: 17 & 18

WGS84 Bounds: -79.8443, 36.2557, -73.3843, 42.2065

PROJCS[“NAD_1983_StatePlane_Maryland_FIPS_1900_Feet”, GEOGCS[“GCS_North_American_1983”, DATUM[“D_North_American_1983”, SPHEROID[“GRS_1980”,6378137.0,298.257222101]], PRIMEM[“Greenwich”,0.0], UNIT[“Degree”,0.0174532925199433]], PROJECTION[“Lambert_Conformal_Conic”], PARAMETER[“False_Easting”,1312333.333333333], PARAMETER[“False_Northing”,0.0], PARAMETER[“Central_Meridian”,-77.0], PARAMETER[“Standard_Parallel_1”,38.3], PARAMETER[“Standard_Parallel_2”,39.45], PARAMETER[“Latitude_Of_Origin”,37.66666666666666], UNIT[“Foot_US”,0.3048006096012192]]

http://spatialreference.org/ref/sr-org/6654/html/

Deep Creek Lake 79°18'56.63"W -79.31573056 39°30'31.66"N 39.50879444

======================================================= Latitude Longitude Datum Zone INPUT = N393031.66 W0791856.63 NAD83 1900

NORTH(Y) EAST(X) AREA CONVERGENCE SCALE METERS METERS DD MM SS.ss

207017.263 200860.407 MD -1 27 12.35 1.00001081

Rockville Latitude: 39° 05’ 02" N Longitude: 077° 09’ 11" W

======================================================= Latitude Longitude Datum Zone INPUT = N390502.0 W0770911.0 NAD83 1900

NORTH(Y) EAST(X) AREA CONVERGENCE SCALE METERS METERS DD MM SS.ss

157329.915 386757.601 MD -0 5 45.83 0.99995642

Easting value (1939 grid) + 512,420 feet = Easting value (1987 grid) Northing value (1939 grid) + 60,750 feet = Northing value (1987 grid).

http://en.wikipedia.org/wiki/Foot_(unit)#Survey_foot “The United States survey foot is defined as exactly 1200⁄3937 meter, approximately 0.3048006096 m” -> or 1 m = 3.280833333 ft One usually finds: 0.3048 m -> or 1 m = 3.280839895 ft

Beginning July 1959 the length of the international yard in the United States and countries of the Commonwealth of Nations was defined as 0.9144 meter. Consequently, the international foot is defined to be equal to exactly 0.3048 meter.

Boatslip Locations.

The boat slip locations were determined from an aerial photograph with Google Earth. That photograph has since disappeared. I did a limited recreation of boatslips with another aerial photograph to validate the process and accuracy of the orginal data set. That validation is described in an other note on this website