THE DEFLEC99 README FILE ------------------------ Version: January 12, 2000 das/drr The DEFLEC99 DEFLECTION OF THE VERTICAL MODELS ---------------------------------------------- You have received these models on CD-ROM, or downloaded them from the National Geodetic Survey (NGS) web site or the NGS FTP site. Files you may have received include: INTD.EXE (PC) or The deflection interpolation program (source code is INTD (Sun) INTD.FOR (PC) or INTD.F (Sun)) XNTD.EXE (PC) or Program for extracting, translating (ascii/binary) XNTD (Sun) and yielding statistics of deflection files (source code is XNTD.FOR (PC) or INTD.F (Sun)) DOSXMSF.EXE (PC) 32-bit DOS extender (needed for running INTD.EXE on a 386 PC) The following file names are valid for PC or Sun (if, however, you downloaded the ASCII versions of these files, the suffix will be ".asc" rather than ".bin"): x1999u01.bin & e1999u01.bin DEFLEC99 grids #1 for CONUS (40-58N, 230-249E) x1999u02.bin & e1999u02.bin DEFLEC99 grids #2 for CONUS (40-58N, 247-266E) x1999u03.bin & e1999u03.bin DEFLEC99 grids #3 for CONUS (40-58N, 264-283E) x1999u04.bin & e1999u04.bin DEFLEC99 grids #4 for CONUS (40-58N, 281-300E) x1999u05.bin & e1999u05.bin DEFLEC99 grids #5 for CONUS (24-42N, 230-249E) x1999u06.bin & e1999u06.bin DEFLEC99 grids #6 for CONUS (24-42N, 247-266E) x1999u07.bin & e1999u07.bin DEFLEC99 grids #7 for CONUS (24-42N, 264-283E) x1999u08.bin & e1999u08.bin DEFLEC99 grids #8 for CONUS (24-42N, 281-300E) x1999a01.bin & e1999a01.bin DEFLEC99 grids #1 for Alaska (60-72N, 172-204E) x1999a02.bin & e1999a02.bin DEFLEC99 grids #2 for Alaska (60-72N, 202-234E) x1999a03.bin & e1999a03.bin DEFLEC99 grids #3 for Alaska (49-61N, 172-204E) x1999a04.bin & e1999a04.bin DEFLEC99 grids #4 for Alaska (49-61N, 202-234E) x1999h01.bin & e1999h01.bin DEFLEC99 grids #1 for Hawaii (18-24N, 199-206E) x1999p01.bin & e1999p01.bin DEFLEC99 grids #1 for Puerto Rico/VI (15-21N, 291-296E) To Install: 1) Make a subdirectory on your hard disk. 2) Copy the various deflection files into that subdirectory. You need not put the deflection files in the same directory as the programs. 4) If you are using a PC, check your AUTOEXEC.BAT and CONFIG.SYS files to insure compliance with the following notes: Note 1: If you are running a 16-bit PC (such as a 386), then DOSXMSF.EXE must either be present in the same directory as INTD.EXE, or, it must be in a directory in your DOS PATH environment variable (such as: c:\dos). DOSXMSF.EXE may be freely reproduced and distributed, without royalty. Note 2: You must have a statement FILES=35 (or a number greater than 35) in your CONFIG.SYS file. To Execute (PC or Sun) Type INTD , and follow the prompts. To Terminate You can stop the program at any time by the Control C key combination. BUT, PLEASE DON'T START YET. PLEASE KEEP READING THIS DOCUMENT. Check The Byte Counts of all Downloaded Files --------------------------------------------- Before beginning, it will be useful to ensure that all files you have received are the correct size. (Download problems are often manifested by incorrect byte counts in the files). Check with the list below to make sure your files match these numbers exactly. PC or Sun Data (counts are good for e1999***.bin files too): x1999u**.bin 4,933,728 bytes x1999a**.bin 5,540,208 bytes x1999h01.bin 607,968 bytes x1999p01.bin 434,688 bytes ASCII Data (counts are good for e1999***.bin files too): x1999u**.asc 12,488,896 bytes (uncompressed) x1999a**.asc 14,024,273 bytes (uncompressed) x1999h01.asc 1,539,044 bytes (uncompressed) x1999p01.asc 1,100,429 bytes (uncompressed) PC executables: INTD.EXE 194,048 bytes XNTD.EXE 165,888 bytes DOSXMSF.EXE 393,942 bytes Sun executables: INTD 148,012 bytes XNTD 67,852 bytes How Program INTD Works ----------------------- The various deflection grids are stored in the ".bin" files. Program INTD will prompt you for the name of the directory where you have chosen to store the .bin files, as well as prompting you for which deflection model you wish to use. You can operate with as few as one pair of .bin files, or as many as 14 pairs. When the program interpolates a given point, it checks an internal list of .bin boundaries, and uses the earliest list entry whose boundaries contain that point (EXCEPTION: In the northwest USA, there is a small overlap between the CONUS x1999u01.bin/e1999u01.bin files and the Alaska x1999a04.bin/e1999a04.bin files In this case, if the CONUS files are available, they will take precedence over the Alaska files). The order in which the .bin file names appear on the opening screen indicates the order in which the .bin files are searched. When running program INTD.EXE (PC) or INTD (Sun), the latitude and longitude of each point must be input. The DEFLEC99 models are relative to the NAD 83 ellipsoid. However, latitudes and longitudes in the ITRF97/GRS-80 and WGS84(G873) systems are very close to those of the NAD 83 system (with only 1-2 meters of horizontal shift.) So any of these types of latitude and longitude (NAD 83, ITRF97, WGS84) may be input, without affecting the interpolated deflection value. This does *not* imply that the deflections are relative to a different ellipsoid. Using NAD 83 latitudes and longitudes interchangeably with ITRF97/GRS-80 or WGS84 latitudes and longitudes is merely an acceptable horizontal approximation. DEFLEC99 deflections, will always be relative to the NAD83 ellipsoid. Do *NOT* use NAD 27 latitudes and longitudes. The horizontal shifts between NAD 83 and NAD 27 can exceed 100 meters, causing a noticeable difference in the interpolated deflection value. To convert from NAD 27 to NAD 83 latitudes and longitudes you may use programs NADCON or CORPSCON, available from NGS. Data Input ---------- You can key data by hand, point by point, or you can create an input file using a text editor. Several file formats are provided, including the NGS "Blue Book" format. These formats are detailed in a "Help" menu option which appears if you specify that you wish to use an input file. Data Output ----------- Results may be collected into an output file. There is no default output file name. The format of the output file is linked to the format of the input file to maintain consistency. If, however, you input your data by keyboard, and ask for an output file, the format of that output file will be in the format known as "Free Format, Type 1". ========================> THE SENSE OF THE SIGNS <=========================== A positive meridian component of deflection of the vertical (Xi) indicates that the astronomic latitude will fall to the north of the corresponding geodetic latitude of the point. A positive prime-vertical component of deflection of the vertical (Eta) indicates that the astronomic longitude will fall to the east of the corresponding geodetic longitude of the point. The computed Laplace correction (Hor.Laplace) should be ADDED to a clockwise astronomic azimuth, to obtain a "near-geodetic" Laplace azimuth. Note: the deflection correction is usually negligible, yielding a geodetic azimuth. Note: in many textbooks, the Laplace correction is shown with the opposite sign and is subtracted from astronomic azimuth. The DEFLEC96 Model ------------------ The DEFLEC96 model was computed by first computing geoid slopes from the GEOID99 model, to get deflections of the vertical at the geoid. In order to have the deflections refer to the surface of the Earth (and not to sea level), a correction for the curvature of the plumbline was included. The Laplace Correction ---------------------- An azimuth measured with a theodolite is an astronomic azimuth. It refers to an azimuth expressed in a local horizon coordinate system aligned along the local gravity vector (line of the plumb bob). A geodetic azimuth, on the other hand, is expressed about a local normal to the ellipsoid. An astronomic azimuth is converted into a geodetic azimuth by applying the Laplace correction. The Laplace correction typically takes one of two forms: The Simplified Laplace Correction (Hor. Laplace) : - Eta x Tangent(Geodetic Latitude) The Complete (Extended) Laplace Correction: - Eta x Tangent(Geodetic Latitude) - [Xi x Sine(Azimuth) - Eta x Cosine(Azimuth)] x Cotangent(Zenith Dist.) The second term is known as the deflection correction, and it is negligible for horizontal lines of sight. The output from INTD provides not only the Xi and Eta components of deflection of the vertical, but also provides the horizontal (simplified) Laplace correction. The sense of the sign is such that one should ADD the correction from program INTD (Hor. Laplace) to an astronomic azimuth that is measured clockwise, thereby obtaining a "Laplace Azimuth." Such an azimuth does not contain the deflection correction, and is suitable for encoding into a *60* "Horizontal Blue-Book" record. The XNTD Utility Program ------------------------ The XNTG program can perform various functions, none of which are required to use the INTD program. The functions of XNTD are the extraction of sub-grids from the provided deflection grids, the translation between ASCII and binary grids, and the reporting of basic statistics for deflection grids. Future Plans ------------ Due to the quickly expanding availability of GPS data on leveled bench marks in the NGS database, there is some incentive to providing annual geoid models, and their associate deflection models, which reflect the latest GPS/BM data. For More Information -------------------- For Products Available From the National Geodetic Survey: Information Services Branch National Geodetic Survey, NOAA, N/NGS12 301-713-3242 fax: 301-713-4172 For Information on DEFLEC99 and Future Research: Dr. Dru A. Smith National Geodetic Survey, NOAA, N/NGS5 301-713-3202 Internet: dru@ngs.noaa.gov Dr. Daniel R. Roman National Geodetic Survey, NOAA, N/NGS5 301-713-3202 Internet: droman@ngs.noaa.gov Visit our web site: http://www.ngs.noaa.gov/DEFLEC/DEFLEC99/deflec99.html