HTDP USER'S GUIDE
(Software Version 2.9)
December 19, 2006
Richard A. Snay
National Geodetic Survey, NOAA
1315 East-West Highway, Room 9115
Silver Spring, Maryland 20910
tel: 301-713-3202 (ext. 154)
fax: 301-713-4327
email: Richard.Snay@noaa.gov
INTRODUCTION
The HTDP (Horizontal Time-Dependent Positioning) software enables users to predict horizontal displacements and/or horizontal velocities related to crustal motion in the United States and its territories. The software also enables users to update positional coordinates and/or geodetic observations to a user-specified date. HTDP supports these activities for coordinates in the North American Datum of 1983 (NAD_83) as well as in all official realizations of the International Terrestrial Reference Frame (ITRF) [Altamimi et al., 2002] and all official realizations of the World Geodetic System of 1984 (WGS 84) [Merrigan et al., 2002]. Accordingly, HTDP may be used to transform positional coordinates between any pair of these reference frames in a manner that rigorously addresses differences in the definitions of their respective velocity fields. HTDP may also be used to transform velocities between any pair of these reference frames.
The software employs models that address both the continuous and the episodic components of crustal motion. For characterizing continuous motion, the models assume that points on the Earth's surface move with constant horizontal velocities. This assumption is generally acceptable except for the accelerated motion experienced during the years immediately following a major earthquake and for the motion associated with volcanic/magmatic activity. For characterizing the episodic motion associated with earthquakes, the models use the equations of dislocation theory (Okada, 1985). Table 1 identifies the dislocation models that are incorporated into HTDP.
HTDP determines velocities for points located in the western 48 states (longitudes between 111W and 125W) by interpolating published velocities for individual sites. The interpolation method has been described by Snay et al. [1996]. The published velocities being interpolated were derived by many researchers [SCEC, 1998; Khazaradze, 1999; WUSC, 2000; Bock et al., 2000; Schenewerk, 2000; and McCaffrey, 2000] from various types of geodetic observations, including GPS (Global Positioning System), EDM (electronic distance measurements), and VLBI (very long baseline interferometry).
Internal to the software, velocities are expressed relative to the assumption that the interior of the North American tectonic plate does not move on average. That is, velocities are expressed relative to the NAD 83 reference frame. When computing velocities for points that are not located in the previously specified regions nor on the North American plate, the software uses the NUVEL1-A model of DeMets et al. [1994] to calculate how such points move relative to the North American tectonic plate. Velocities relative to other reference frames are converted from their corresponding NAD 83 velocities using transformation equations adopted by the National Geodetic Survey.
SOFTWARE CHARACTERISTICS
The source code is written in FORTRAN-77 and resides in the file, HTDP.FOR. The user needs to compile and link this source code to create executable code that is compatible with the operating system on his/her computer. For convenience, the National Geodetic Survey distributes a file called, HTDP.EXE, which contains executable code that will work on Windows95, WindowsNT, and Windows98.
The software is menu-driven and most information is entered interactively. Users may also enter certain information in the so-called "blue-book" format for horizontal control data (see Federal Geodetic Control Subcommittee, 2000). For example, if requested, the software will predict displacements and/or velocities for all stations having an *80* record in an existing blue-book file. Besides predicting displacements and/or velocities for individual points, the software will predict these quantities for a set of points which defines a 2-dimensional array on the Earth's surface or which defines an equally spaced 1-dimensional array along a geodesic curve on the Earth's surface. In all cases the output is written to a user-specified file.
The software also has the capability to update positional coordinates and/or geodetic observations to a user-specified date. For such an application, the user must specify the horizontal coordinates (latitudes and longitudes) and/or the observed values for one date, and the software will predict corresponding values for another user-specified date. The software can update various observational types, all of which may be encoded in blue-book format. In particular, the software accepts direction observations, angle observations, distance observations, azimuth observations, and GPS observations.
AUXILIARY INFORMATION
This User's Guide contains a set of five exercises to familiarize people with some of the HTDP applications. Also, Snay [1999] discusses the HTDP software and its applications in considerable detail. Moreover, the National Geodetic Survey maintains a LOG that summarizes modifications to the software in chronological order. Finally, people may run a version of HTDP interactively on the world-wide-web. Set your browser to http://www.ngs.noaa.gov/ and click on "geodetic tool kit" and then on "HTDP".
DISCLAIMER
This software and supporting information is furnished by the Government of the United States of America, and is accepted/used by the recipient with the understanding that the U.S. Government makes no warranties, expressed or implied, concerning the accuracy, completeness, reliability, or suitability of this software, of its constituent parts, or of any supporting data.
The Government of the United States of America shall be under no liability whatsoever resulting from the use of this software. This software should not be relied upon as the sole basis for solving a problem whose incorrect solution could result in injury to person or property.
This software is the property of the Government of the United States of America. Therefore, the recipient further agrees not to assert proprietary rights therein and not to represent this software to anyone as being other than U.S. Government software.
Table 1--Dislocation Models incorporated into HTDP
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Earthquake Source of Model
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CALIFORNIA
06-07-1934 Parkfield (M=6.0) Segall and Du, 1993
05-17-1940 El Centro (M=6.9) Snay and Herbrectsmeier, 1994
07-01-1941 Red Mountain (M=5.9) Snay (unpublished)
10-21-1942 San Jacinto (M=6.6) Snay and Herbrectsmeier, 1994
07-21-1952 Kern County (M=7.5) Snay and Herbrectsmeier, 1994
03-19-1954 San Jacinto (M=6.4) Snay and Herbrectsmeier, 1994
06-26-1966 Parkfield (M=5.6) Segall and Du, 1993
04-09-1968 Borrego Mtn. (M=6.5) Snay and Herbrectsmeier, 1994
02-09-1971 San Fernando (M=6.6) Snay and Herbrectsmeier, 1994
03-15-1979 Homestead Valley (M=5.6) Stein and Lisowski, 1983
08-06-1979 Coyote Lake (M=5.9) Snay and Herbrectsmeier, 1994
10-15-1979 Imperial Valley (M=6.4) Snay and Herbrectsmeier, 1994
05-02-1983 Coalinga (M=6.4) Stein and Ekstrom, 1992
04-24-1984 Morgan Hill (M=6.2) Snay and Herbrectsmeier, 1994
08-04-1985 Kettleman Hill (M=6.1) Ekstrom et al., 1992
07-08-1986 N. Palm Springs (M=5.6) Savage et al., 1993
07-21-1986 Chalfant Valley (M=6.2) Savage and Gross, 1995
10-01-1987 Whittier Narrow (M=5.9) Lin and Stein, 1989
11-24-1987 Superstition Hill (M=6.6,6.2) Larsen et al., 1992
10-17-1989 Loma Prieta (M=7.1) Lisowski et al., 1990
04-22-1992 Joshua Tree (M=6.1) Bennett et al., 1995
04-25-1992 Cape Mendocino (M=7.1) Oppenheimer et al., 1993
06-29-1992 Landers/Big Bear (M=7.5,6.6) Hudnut et al., 1994
01-17-1994 Northridge (M=6.7) Hudnut et al., 1996
10-16-1999 Hector Mine (M=7.1) Peltzer, Crampe, & Rosen, 2001
12-22-2003 San Simeon (M=6.5) Johanson, (in prep.)
10-28-2004 Parkfield (M=6.0) Johanson et al., 2006
ALASKA
03-28-1964 Prince William Sound (M=9.2) Holdahl and Sauber, 1994
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REFERENCES
Altamimi, Z, Sillard P, Boucher C (2002) ITRF2000: A new release of the International Terrestrial Reference Frame for earth science applications. J Geophysical Research 107(B10):ETG2/1-19
Bennett RA, Reilinger RE, Rodi W, Li Y, Toksoz MN, Hudnut K (1995) Coseismic fault slip associated with the 1992 MW 6.1 Joshua Tree, California, earthquake: Implications for the Joshua Tree-Landers earthquake sequence. J Geophys Res 100:6443-6461
Bock Y Fang P, Nikolaidis R, van Domselaar M (2000) personal communication of files containing velocities for continuous GPS sites in the western U.S. and for sites in the California High Accuracy reference network (HARN)
DeMets C, Gordon RG, Argus DF, Stein S (1994) Effect of recent revisions to the geomagnetic reveral time scale on estimates of current plate motions, Geophys Res Let, 21:2191-2194
Ekstrom E, Stein RS, Eaton JP, Eberhart-Phillips D (1992) Seismicity and geometry of a 110-km-long blind thrust fault, 1, the 1985 Kettleman Hills, California, earthquake. J Geophys Res 97:4843-4864
Federal Geodetic Control Subcommittee (2000) Input formats and specifications of the National Geodetic Survey data base: Volume I. Horizontal control data. National Geodetic Information Branch, NOAA, Silver Spring, Maryland, 20910 (http://www.ngs.noaa.gov/FGCS/BlueBook/)
Holdahl SR, Sauber J (1994) Coseismic Slip in the 1964 Prince William Sound Earthquake: A New Geodetic Inversion. Pure and Applied Geophys 142:55-82
Hudnut KW and 16 others (1994) Co-seismic displacements of the 1992 Landers earthquake sequence. Bull Seismol Soc Am 84:625-645
Hudnut KW and 10 others (1995) Co-seismic displacements of the 1994 Northridge, California, Earthquake, Bull Seismol Soc Am 86:S19-S36
Hurst KJ, Argus DF, Donnellan A, Heflin MB, Jefferson DC, Lyzenga GA, Parker JW, Smith M, Webb FH, and Zumberge, JF (2000) The coseismic geodetic signature of the 1999 Hector Mine Earthquake. Geophys Res Letters 27:2733-2736. See also http://milhouse.jpl.nasa.gov/hector/hectormine3.model .
Johanson, Ingrid A., Ric J. Fielding, Frederique Rolandone, and Roland Burgmann (2006) Coseismic and postseismic Slip of the 2004 Parkfield earthquake, Bull.Seismol. Soc. Am., 96, S269-S282.
Johanson, I., Ph.D. Dissertation, Univ. of California, Berkeley, in prep.
Khazaradze G, Qamar A, Dragert H (1999) Tectonic deformation in western Washington from continuous GPS measurements, Geophys Res Let, 20:3153-3156
Larsen S, Reilinger R, Neugebauer H, Strange W (1992) Global Positioning System measurements of deformations associated with the 1987 Superstition Hills earthquake: evidence for conjugate faulting. J Geophys Res 97:4885-4902
Lin J, Stein RS (1989) Coseismic folding, earthquake recurrence, and the 1987 source mechanism at Whittier Narrows, Los Angeles Basin, California. J Geophys Res 94:9614-9632
Lisowski M, Prescott WH, Savage JC, Johnston MJ (1990) Geodetic estimate of coseismic slip during the Loma Prieta, California, earthquake. Geophys Res Lett 17:1437-1441
McCaffrey R, Long MD, Goldfinger C, Zwick PC, Nabelek JL, Johnson CK, and Smith C (2000) Rotation and plate locking at the southern Cascadia subduction zone, Geophys Res Let, 27: 3117-3120
McCarthy DD (1996) IERS Conventions (1996). IERS Technical Note 21,Observatoire de Paris
Merrigan MJ, Swift ER, Wong RF, Saffel JT (2002) A refinement to the World Geodetic System 1984 reference frame, Proceedings of the Institute of Navigation GPS-2002, Portland, Oregon, Sept. 2002, in press
Okada Y (1985) Surface deformation due to shear and tensile faults in a half-space. Bull Seismol Soc Amer 75:1135-1154
Oppenheimer D and 19 others (1993) The Cape Mendocino, California earthquake sequence of April, 1992: subduction at the triple junction. Science 261:433-438
Peltzer G, Crampe, F, and Rosen P (2001) The Mw 7.1, Hector Mine, California earthquake: surface rupture, surface displacement field, and fault slip solution from ERS SAR data. C. R. Acad. Sci. Paris, 333:545-555
( http://www-radar.jpl.nasa.gov/insar4crust/HME/ )
Savage JC, Gross WK (1995) Revised dislocation model of the 1986 Chalfant Valley earthquake, eastern California. Bull Seismol Soc Am 85:629-631
Savage JC, Lisowski M, and Murray M (1993) Deformation from 1973 through 1991 in the epicentral area of the 1992 Landers, California, earthquake (MS = 7.5). J Geophys Res 98:19951-19958
SCEC (Southern California Earthquake Center) (1998) Horizontal deformation velocity map, version 2.0,
http://www.scecdc.scec.org/group_e/release.v2/index.html
Schenewerk MS, Marshall J, Dillinger W, Cline M, Eckl M, Weston N (2000) estimating North American CORS coordinates in a consistent fashion within the framework of global network solution, EOS, Transactions of the American Geophysical Union, 2000 Spring Meeting (abstract), S169
Segall P, Du Y (1993) How similar were the 1934 and 1966 Parkfield earthquakes?, J Geophys Res 98:4527-4538
Snay RA (1999) Using the HTDP software to transform spatial coordinates across time and between reference frames, Surveying and Land Information Systems, 59:15-25
Snay RA, Herbrectsmeier E (1994) The TDP-H91-CA model for historical horizontal deformation in California. Manuscripta Geodaetica 19:180-198
Snay RA, Cline MW, Philipp CR, Jackson DD, Feng Y, Shen ZK, Lisowski M (1996) Crustal velocity field near the big bend of California's San Andreas fault. J Geophys Res 101:3173-3185
Stein RS, Ekstrom G (1992) Seismicity and geometry of a 110-km-long blind thrust fault, 2, synthesis of the 1982-1985 California earthquake sequence. J Geophys Res 97:4865-4884
Stein RS, Lisowski M (1983) The 1979 Homestead Valley earthquake sequence, California: Control of aftershocks and postseismic deformation. J Geophys Res 88:6477-6490
WUSC (2000) Welcome to the Western U.S. Cordillera (WUSC) Deformation project homepage! Solution version 002:
http://cfa-www.harvard.edu/space_geodesy/WUSC/
HTDP EXERCISES
June 1, 2001
The following set of exercises are designed to familiarize the user with several capabilities of the HTDP software. Angular
brackets identify text that the user should type into the computer. For example, in response to the instruction, "enter <abc>," the
user should type "abc" and then hit the ENTER key or the RETURN
key.
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EXERCISE 1. Predicting velocities at individual points
1.1 Enter <htdp.exe> to start the program. Some introductory information should now be displayed on the computer's screen. Hit the ENTER key or the RETURN key to obtain the "MAIN MENU."
1.2 Enter <2> to indicate that you will be predicting velocities.
1.3 Enter a name for the file that will contain the predicted velocities (for example, vfile).
1.4 Enter <1> to indicate that velocities will be predicted relative to the NAD_83 reference frame.
1.5 Enter <1> to indicate that you will be entering positional coordinates for individual points in an interactive manner.
1.6 Enter <alpha> for the name of the first point whose velocity will be predicted.
1.7 Enter <1> to specify that you will provide a latitude and a longitude.
1.8 Enter <38,6,12.96> to denote that the latitude of alpha is
38o 06' 12.96" N.
1.9 Enter <122,56,7.80> to denote that the longitude of alpha is 122o 56' 7.80" W.
1.10 Enter <0.> to denote that the ellipsoid height of alpha is 0. meters.
The screen should now be displaying the following information:
Northward velocity = 33.96 mm/yr.
Eastward velocity = -21.81 mm/yr.
Upward velocity = 0.00 mm/yr.
X-dim. velocity = -6.91 mm/yr.
Y-dim. velocity = 29.45 mm/yr.
Z-dim. velocity = 26.73 mm/yr.
1.11 The screen should also be displaying the menu for continuing. Enter <1> to predict the velocity for another point.
1.12 Enter <beta> for the name of this second point.
1.13 Enter <1> to specify that you will provide a latitude and a longitude.
1.14 Enter <36,40,11.28> to specify the latitude of beta.
1.15 Enter <121,46,19.92> to specify the longitude of beta.
1.16 Enter <0.> to specify the ellipsoid height of beta.
The screen should now be displaying the following information:
Northward velocity = 35.90 mm/yr.
Eastward velocity = -27.68 mm/yr.
Upward velocity = 0.00 mm/yr.
X-dim. velocity = -12.24 mm/yr.
Y-dim. velocity = 32.80 mm/yr.
Z-dim. velocity = 28.80 mm/yr.
1.17 If you wish to predict velocities for additional points, then you may enter <1> and proceed as before. Otherwise, enter <0> to return to the main menu.
At this time, it is instructive to inspect the output file
that contains the predicted velocities. This is the file whose
name was specified in Step 1.3. If you have a windowing capability, then you may open another window to read this file. Otherwise, enter <0> to exit the HTDP software so that you may read this file. Note that this file contains all the information
pertinent to the velocities that were predicted.
1.18 If you exited the program, enter <htdp.exe> to restart it and then enter <2> to predict more velocities. If you did not exit the program, just enter <2>.
1.19 Enter a name for a new file that will contain the additional velocities to be predicted. (Caution: if you enter the same name as was entered in Step 1.3, then the software will overwrite the previous file.)
1.20 Enter <0> to indicate that the following velocities will be calculated relative to a specified point having a specified velocity.
1.21 Enter <alpha> for the name of the reference point.
1.22 Enter <1> to specify that you will provide a latitude and a longitude.
1.23 Enter <38,6,12.96> for the latitude of alpha.
1.24 Enter <122,56,7.80> for the longitude of alpha.
1.25 Enter <0.> for the ellipsoid height of alpha.
1.26 Enter <5.> to indicate that the northward velocity of alpha is to be 5.00 mm/yr.
1.27 Enter <0.> to indicate that the eastward velocity of alpha is to be 0.00 mm/yr.
1.28 Enter <1> to indicate that you will be specifying individual points in an interactive manner.
1.29 Enter <beta> for the name of the first point whose velocity relative to alpha is to be predicted.
1.30 Enter <1> to specify that you will provide a latitude and a longitude.
1.31 Enter <36,40,11.28> for the latitude of beta.
1.32 Enter <121,46,19.92> for the longitude of beta.
1.33 Enter <0.> for the ellipsoid height of beta.
The screen should now be displaying the following information:
Northward velocity = 6.94 mm/yr.
Eastward velocity = -5.87 mm/yr.
Upward velocity = 0.00 mm/yr.
X-dim. velocity = -2.81 mm/yr.
Y-dim. velocity = 6.62 mm/yr.
Z-dim. velocity = 5.57 mm/yr.
Note that 6.94 = 35.90 - 33.96 + 5.00 where
38.85 is the northward velocity of beta relative to the NAD_83 reference frame,
31.88 is the northward velocity of alpha relative to the NAD_83 reference frame, and
5.00 is to be the northward velocity of alpha in our local
reference system.
Similarly, the eastward velocity of -5.87 mm/yr equals the
difference between the eastward velocities of beta and alpha in the NAD_83 reference frame.
The astute user may recognize that this formula for computing relative velocities is not mathematically rigorous because of Earth's curvature. The error grows as a function of distance from the reference point.
1.34 Enter <0> to return to the main menu.
This concludes Exercise 1. You may find it instructive to inspect the output file whose name was specified in step 1.19.
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EXERCISE 2. Predicting displacements at individual points.
2.1 If needed, enter <htdp.exe> to start the program. Then hit the ENTER key to obtain the MAIN MENU.
2.2 From the MAIN MENU enter <1> to select the option for predicting displacements between two dates.
2.3 Enter <1,1,1985> to indicate that the first date is January 1, 1985.
2.4 Enter <1,1,1995> to indicate that the second date is January 1, 1995.
2.5 Enter <dfile1> for the name of the output file that is to contain the predicted displacements.
2.6 Enter <1> to specify that positions and velocities will be expressed in the NAD 83 reference frame.
2.7 Enter <1> to indicate that you will enter individual points interactively.
2.8 Enter <beta> for the name of the first point whose displacement from January 1, 1985 to January 1, 1995 is to be predicted.
2.9 Enter <1> to specify that you will provide a latitude and a longitude.
2.10 Enter <36,40,11.28> for the latitude of beta.
2.11 Enter <121,46,19.92> for the longitude of beta.
2.12 Enter <0.> for the ellipsoid height of beta.
2.13 Enter <0> to indicate that the software will predict the velocity to be used in calculating the displacement.
The screen should now be displaying the following information:
Northward displacement = 0.433 meters.
Eastward displacement = -0.278 meters.
Upward displacement = -0.004 meters.
Recall from Exercise 1 that the northward velocity of beta is 35.90 mm/yr. Thus in 10 years beta moved 0.359 meters northward as a result of its continuous motion. To this displacement, the HTDP software adds those displacements associated with major earthquakes. For example, the point beta moved northward 0.074 meters during the Loma Prieta earthquake (M=7.1) of October 18, 1989. The sum of 0.359 meters and 0.074 meters equals the total predicted displacement of 0.433 meters for the 10-year period from January 1, 1985 to January 1, 1995. In the following steps, the displacement that occurred at beta during the Loma Prieta earthquake will be predicted. Before proceeding, however, note that the software predicts an upward displacement of -0.004 meters. This quantity represents the cumulative vertical displacement associated with all earthquakes occurring between January 1, 1985 and January 1, 1995. The software assumes that the vertical component of continuous motion is everywhere zero.
2.14 Enter <0> to return to the main menu.
2.15 Enter <1> to predict displacements.
2.16 Enter <10,16,1989> to indicate that the first date is October 16, 1989.
2.17 Enter <10,18,1989> to indicate that the second date is October 18, 1989.
2.18 Enter <dfile2> to name the output file that is to contain the predicted displacements.
2.19 Enter <1> to specify that positions and displacements will be expressed in the NAD_83 reference frame.
2.20 Enter <1> to indicate that you will specify individual points interactively.
2.21 Enter <beta> for the point's name.
2.22 Enter <1> to specify that you will provide a latitude and a longitude.
2.23 Enter <36,40,11.28> for the latitude of beta.
2.24 Enter <121,46,19.92> for the longitude of beta.
2.25 Enter <0.> for the ellipsoid height of beta.
2.26 Enter <0> to indicate that the software will predict the velocity to be used in calculating the displacement.
The screen should now be displaying the following information:
Northward displacement = 0.074 meters.
Eastward displacement = -0.001 meters.
Upward displacement = -0.004 meters.
Displacements associated with the Loma Prieta earthquake can now be predicted for other locations by entering <1> and responding to the prompts. When finished enter <0> to return to the main menu. You may find it instructive to inspect the output files, dfile1 and dfile2, at this time.
This concludes Exercise 2.
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Exercise 3. Predicting velocities for sets of points.
For predicting velocities, the latitudes and longitudes of the points may be entered in several ways in addition to entering
individual points interactively. The options include (a)
specifying a grid of points, (b) specifying the name of a file that contains the positional information in blue-book format, and (c) specifying a sequence of points on a line (or more precisely, a geodesic curve on Earth's surface). These same options are
available for specifying the latitudes and longitudes of points
where displacements between two dates are to be predicted.
3.1 If needed, enter <htdp.exe> to start the program. Then hit the ENTER key to obtain the MAIN MENU.
3.2 Starting from the MAIN MENU, enter <2> to predict velocities.
3.3 Enter <vfile1> for the name of the output file that is to contain the predicted velocities.
3.4 Enter <1> to predict velocities relative to the NAD_83 reference frame.
3.5 Enter <2> to indicate that the points form a regularly spaced two-dimensional grid on Earth's surface.
3.6 Enter a name to identify the grid (for example, grid1).
3.7 Enter <34,0,0> to indicate that the minimum latitude is
34o00'00" N.
3.8 Enter <35,0,0> to indicate that the maximum latitude is
35o00'00" N.
3.9 Enter <300> to indicate that the latitude spacing is 300 seconds (or equivalently, 5 minutes).
3.10 Enter <118,30,0> to indicate that the minimum longitude is
118o30'00" W.
3.11 Enter <119,10,0> to indicate that the maximum longitude is
119o10'00" W.
3.12 Enter <600> to indicate that the longitude spacing is 600 seconds (or equivalently, 10 minutes).
The screen should now be displaying the menu for specifying additional points at which velocities are to be predicted.
Predicted velocities for the grid are contained in vfile1. To
examine this file, enter <0> to return to the main menu (and if you do not have a windowing capability, enter <0> to exit the HTDP software).
In vfile1, the first point (the southeast corner of the grid) should have the northward velocity of 29.02 mm/yr and the
eastward velocity of -27.97 mm/yr. The last point (the northwest corner) should have the northward velocity of 17.03 mm/yr and the eastward velocity of -17.87 mm/yr.
In the following steps, velocities will be predicted for a set of points in the file BFILE which contains data for the California High Precision Geodetic Network. This file is in blue-book format which is the format adopted by the Federal Geodetic Control Subcommittee for transferring geodetic data. For predicting velocities, the HTDP software uses only the blue-book records that have *80* in columns 7 through 10. Furthermore, the program reads only the following fields on these records
Columns Content FORTRAN format
15-44 name of point A30
45-55 latitude (deg-min-sec) I2,I2,F7.5
56 N or S latitude A1
57-68 longitude (deg-min-sec) I3,I2,F7.5
69 W or E longitude A1
Before predicting velocities for the points in BFILE, it may be instructive to examine the contents of this file, especially the *80* records.
3.13 Follow Steps 3.1 through 3.4 as before except use the name, vfile2, for the output file that will contain the predicted velocities.
3.14 Enter <3> to indicate that the points are in a blue-book file.
3.15 Enter <BFILE> to specify the name of the blue-book file.
The screen should now be displaying the menu for specifying additional points at which velocities are to be predicted. Predicted velocities for the points in BFILE are contained in the file, vfile2.
3.16 To examine vfile2, enter <0> to return to the main menu (and if you do not have a windowing capability, enter <0> to exit the HTDP software).
In vfile2, the first point, AMBOY, should have a northward
velocity of 0.50 mm/yr and an eastward velocity of 1.08 mm/yr. The last point, TOMTIT 2, should have a northward velocity of 24.04 mm/yr and an eastward velocity of -9.63 mm/yr.
In the following steps, we will predict velocities for a
sequence of points that lie along a line that forms a geodesic
curve on Earth's surface.
3.17 Follow Steps 3.1 through 3.4 as before except use the name, vfile3, for the output file that will contain the predicted velocities.
3.18 Enter <4> to indicate that the points lie on a line.
3.19 Enter a name to identify the line (for example, line1).
3.20 Enter <35,17,28.3> to specify the latitude of a point through which the line is to pass. We will refer to this point as the origin.
3.21 Enter <120,15,35.431> to specify the longitude of the origin.
3.22 Enter <90.> to specify that the line is to have an azimuth of 90 degrees when it passes through the origin.
3.23 Enter <-5000.,10000.> to specify that velocities will be predicted for points located between 5000 meters before the origin and 10000 meters after the origin.
3.24 Enter <5000.> to specify that the spacing between the points will be 5000 meters.
The screen should now be displaying the menu for specifying additional points at which the velocities are to be predicted.
Predicted velocities for the points on the line are contained in the file, vfile3.
3.25 To examine vfile3, enter <0> to return to the main menu (and if you do not have a windowing capability, enter <0> to exit the HTDP software).
The first point in vfile3 should have a northward velocity of 30.71 mm/yr and an eastward velocity of -27.94 mm/yr. This file should contain predicted velocities for four points. The second of these points should correspond to the origin. Note that the origin has the highest latitude of the four points because the line forms a geodesic curve whose azimuth is 90 degrees when passing through the origin.
This concludes Exercise 3.
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Exercise 4. Updating positional coordinates at individual points.
4.1 If needed, enter <htdp.exe> to start the program. Then hit the ENTER key to obtain the MAIN MENU.
4.2 Enter <3> to specify that positions will be updated.
4.3 Enter <7,4,1995> to specify that the new coordinates are to correspond to the position of the point on July 4, 1995.
4.4 Enter <1> to specify that positions will be expressed in the NAD 83 reference frame.
4.5 Enter <1> to specify that individual points will be entered interactively.
4.6 Enter <5,7,1991> to specify that the input coordinates are to correspond to the position of the point on May 7, 1991.
4.7 Enter <newfile> for the name of the output file that will contain the updated coordinates.
4.8 Enter <alpha> for the name of the point whose positional coordinates will be updated.
4.9 Enter <1> to specify that you will provide a latitude and a longitude.
4.10 Enter <38,6,12.96> for the latitude of alpha on May 7, 1991.
4.11 Enter <122,56,7.80> for the longitude of alpha on May 7, 1991.
4.12 Enter <0.> for the ellipsoid height of alpha on May 7, 1991.
4.13 Enter <0> to indicate that the software will predict the velocity to be used in updating the position.
The screen should now be displaying the following information:
Updated latitude = 38 06 12.96458N
Updated longitude = 122 56 7.80372W
Updated Ellip. Ht.= 0.000 meters
Updated X = -2732250.866 meters
Updated Y = -4217684.301 meters
Updated Z = 3914499.275 meters
4.14 Enter <n> to indicate that no more coordinates are to be updated at this time.
Examine the file, newfile, at this time. Note that newfile
contains both the old and the new coordinates. Also newfile
contains the velocities and the (total) displacements applied to update the positional coordinates.
This concludes Exercise 4.
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Exercise 5. Update positional coordinates for points in a blue-book file and update the corresponding observations.
5.1 If needed, enter <htdp.exe> to start the program. Then hit the ENTER key to obtain the MAIN MENU.
5.2 Enter <3> to indicate that coordinates and observations will be updated.
5.3 Enter <7,4,1995> to indicate that the updated coordinates and observations are to correspond to July 4, 1995.
5.4 Enter <1> to specify that positions will be expressed in the NAD 83 reference frame.
5.5 Enter <4> to specify that both coordinates and observations are to be updated. Note that options 2 and 3 allow the user to update one without updating the other.
5.6 Enter <1> to indicate a standard blue-book file will be used.
5.7 Enter <BFILE> to indicate that the original coordinates and the non-GPS observations are contained in the file called BFILE.
5.8 Enter <newbf> for the name of the blue-book file that will contain the updated coordinates and the updated non-GPS observations.
5.9 Enter <5,7,1991> to specify that input coordinates correspond to the positions on May 7, 1991. For updating an observation, HTDP uses the date that this observation was performed as the starting date. The date of observation is specified within the blue-book file as part of the corresponding observational record.
5.10 Enter <y> to indicate the existence of a file that contains the GPS observations.
5.11 Enter <GFILE> to specify that the GPS observational records are contained in the file called GFILE.
5.12 Enter <newgf> to specify that the updated GPS records will be contained in the file called newgf.
5.13 Enter <1> to indicate that the GPS vectors are to be transformed to the NAD_83 reference frame.
The screen should now be displaying the main menu. You may wish to examine the files, newbf and newgf, at this time. In newbf, the first *80* record is for station AMBOY. The new latitude for AMBOY should equal 34o 33' 31.04904" N. In newgf, the first C record is for a GPS observation involving the station whose ID is 8635 and the station whose ID is 8476. The updated values for this observation should be 89894.4185 meters in X, -59905.9538 meters in Y, and -16773.7949 meters in Z. Also in newgf, columns 52-53 of the first B record should read "02" to indicate that the updated GPS interstation vector has been transformed to the original WGS_84 reference frame which is equivalent to the NAD_83 reference frame. (Note that post-1994 realizations of WGS_84 are not equivalent to NAD_83.)
This concludes exercise 5.
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