U.S. Cast bg S| g Res Ctr CETA 8 81-13 Products From Two Computer Programs Which Process Digital Bathymetric Data by Barry E. Herchenroder COASTAL ENGINEERING TECHNICAL AID NO. 81-13 OCTOBER 1981 wHol DOCUMENT COLLECTION Approved for public release; distribution unlimited Rast U.S. ARMY, CORPS OF ENGINEERS Tt COASTAL ENGINEERING e RESEARCH CENTER ee Kingman Building no. Fort Belvoir, Va. 22060 o9W30 Reprint or republication of any of this material shall give appropriate credit to the U.S. Army Coastal Engineering Research Center. Limited free distribution within the United States of single copies of this publication has been made by this Center. Additional copies are available from: Nattonal Technical Informatton Service ATTN: Operations Divtston 5285 Port Royal Road Springfteld, Virginia 22161 The findings in this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents. IY 0 03 WT b3 3 ANA UNCLASSIFIED SECURITY CLASSIFICATION OF THIS PAGE (When Data Entered) REPORT DOCUMENTATION PAGE SEE Oo ee eee 1. REPORT NUMBER 2. GOVT ACCESSION NO|| 3. RECIPIENT'S CATALOG NUMBER CETA 81-13 4. TITLE (end Subtitle) 5. TYPE OF REPORT & PERIOD COVERED Coastal Engineering Technical Aid 6. PERFORMING ORG. REPORT NUMBER PRODUCTS FROM TWO COMPUTER PROGRAMS WHICH PROCESS DIGITAL BATHYMETRIC DATA 7. AUTHOR(s) 8. CONTRACT OR GRANT NUMBER(s) Barry E. Herchenroder 9. PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT, PROJECT, TASK AREA & WORK UNIT NUMBERS Department of the Army Coastal Enginering Research Center (CERRE-CO) A31592 Kingman Building, Fort Belvoir, Virginia 22060 11. CONTROLLING OFFICE NAME AND ADDRESS 12. REPORT DATE Coastal Engineering Research Center Kingman Building, Fort Belvoir, Virginia 22060 16 14. MONITORING AGENCY NAME & ADDRESS(if different from Controlling Office) | 15. SECURITY CLASS. (of thie report) UNCLASSIFIED 15a. DECL ASSIFICATION/ DOWNGRADING SCHEDULE 16. DISTRIBUTION STATEMENT (of this Report) Approved for public release; distribution unlimited. - DISTRIBUTION STATEMENT (of the abstract entered in Block 20, if different from Report) 18. SUPPLEMENTARY NOTES - KEY WORDS (Continue on reverse side if necessary and identify by block number) Computer programs Digital bathymetric data ABSTRACT (Continue on reverse side if necesaary and identify by block number) A description is given of products from two computer programs which process digital bathymetric data. One program generates regularly spaced bathymetric data from irregularly spaced data. The other uses regularly spaced data to determine and draw contours. A large set of irregularly spaced bathymetric data available on magnetic tape for U.S. coastal regions is also described. Examples of output from each program are displayed for two coastal areas. 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A PITRE ieule meray atone 1 + Poe ee eo ipa eager ee, ee Ps cores sca Pedele dotiw kendo ; oithaues Crylid) apeen® 2 een heh eerie ieee i he CR ad ue Tonle Se hoe Pa be hes CS 223 gooy aoa) (te a eget ae + di, ee. Liv tiara et Bhuye3 Ande Tendo, et» aah bsotis tn B uy nen ae get, tae ae vi Aiba Seb. ea pals ith uae ovens ey Nonna: away ie Dk B ie Laven baw tadannn ity 07, oa. prapshisn PREFACE This report describes products from two computer programs, and a set of digital bathymetric data for U.S. coastal regions. The programs and data are useful for generating regularly spaced bathymetric data and determining and drawing contours. The work was carried out under the waves and coastal flood- ing research program of the U.S. Army Coastal Engineering Research Center (CERC). The present report was prepared by Dr. Barry E. Herchenroder, under the general supervision of Dr. C.L. Vincent, Chief, Coastal Oceanography Branch, Research Division. Comments on this publication are invited. Approved for publication in accordance with Public Law 166, 79th Congress, approved 31 July 1945, as supplemented by Public Law 172, 88th Congress, approved 7 November 1963. Colonel, Corps of Engineers Commander and Director 1s mS “fh f “4 a mu i ro “a he: is go jade bie ‘celliteerig roses | gxe eaeb bre emstgosq, ett bas _pakiroiy oa bina Aspb, ‘9d¢ s5ba0 ‘waliercont eit a carrey eh surah : donee tala Susaney' aie ony whe eesuacs A188 att vel abides vd- bedaomelqqus cy ee on ; ‘ i ! CORE arsontgnd ‘to egro) ,lseofod rolpewiG fins. Tabs sme CONTENTS CONVERSION FACTORS, U.S. CUSTOMARY TO METRIC (SI). ......... DENTE ROD U GEL O Niessen sssenrstenet rere sveier sweetest eae ier seers secs ts ng ely SSH eS MTSE STEENS RCT aS ET BNOSDDEECTLALA DATA plow Sot othe hoc fame: Sei AL SUMee tel To bela cmtetnrs co Cxcu mee ial; SPROGRAMEZERED TMS, SHEP ee et CO MoS. <. SRE CR ARR IY TRIROGRVA, GOIMOR. 6 you, Goo 6 obeo 6 lo OO OO HO Gi sde oid O10. 0) a 6 WW IGMOCIU MONS 546 Glo te lo Me veo oF 06 OOo oO 60 6 6 0 06 610 6 6 de AGE RIG DT Lila ett ilirida aN CR kame Stic eS E'.. Aonel Cralicy Gimmepubcraicl lesa ko Ze CONTOR eee eh ee ce ies is et a tee Seah ere MPR te Rent ee tenet Tate Ae Meat tates WIL SURIMINES C65 9 0 6 Oo oe 8 0 8 Oo 0 0 oo OO 0 Fo oo 8 IAIN, GID) 5 56 o 6 0 60 6 6 0 oO OOO oO OOOO OO FIGURES 1 Index (1° square areas) to hydrographic data (except those of the Migiestn COASIE) |G UOSO wo USGS omilyy 6 666) S696 6 6 66'S 6 Bs 6 6 6 2 Index (1° square areas) to hydrographic data off the Alaskan coast, IS)EKO) Mefoy ALENa sop BY OM ao OO Tauc eG, failG Oral. ch don te moron on nue: IGG” co oroe 3 ZGRID1-produced soundings offshore of Great Egg Harbor Inlet, New: Jerseysyinwar 0.03" squarewarea,. <0.) cu.) seemed Rwy © Teach shone 4 ZGRID1-produced bed elevations near CERC's FRF at Duck, North Carolina 5 ZGRIDI1- produced regularly spaced depth values for the same area off of Great Egg Harbor Inlet, New Jersey, covered by Figure 3. ..... 6 CONTOR-produced depth contours for the same area off of Great Harbor Inlet, New Jersey, covered by Figures 3 and5 .......... 7 CONTOR-produced depth contours for the same region near CERC's FRF covered iby halguret Ayia.) tsetse c's KS RMU AL. Vd ees Page 15 16 10 11 12 13 14 14 CONVERSION FACTORS, U.S. CUSTOMARY TO METRIC (SI) UNITS OF MEASUREMENT U.S. customary units of measurement used in this report can be converted to metric (SI) units as follows: Multiply by To obtain inches 25.4 millimeters 2.54 centimeters square inches 6-452 square centimeters cubic inches 16.39 cubic centimeters feet 30.48 centimeters 0.3048 meters square feet 0.0929 Square meters cubic feet 0.0283 cubic meters yards 0.9144 meters Square yards 0.836 square meters cubic yards 0.7646 cubic meters miles 1.6093 kilometers square miles 259.0 hectares knots 1.852 kilometers per hour acres 0.4047 hectares foot-pounds 1.3558 newton meters ILIA EES LeON@ Ve 1072 kilograms per square centimeter ounces 28.35 grams pounds 453.6 grams 0.4536 kilograms ton, long 1.0160 metric tons ton, short 0.9072 metric tons degrees (angle) 0.01745 radians Fahrenheit degrees 5/9 Celsius degrees or Kelvins! 1To obtain Celsius (C) temperature readings from Fahrenheit (F) readings, use formula: C = (5/9) (F -32). To obtain Kelvin (K) readings, use formula: K = (5/9) (F -32) + 273.15. PRODUCTS FROM TWO COMPUTER PROGRAMS WHICH PROCESS DIGITAL BATHYMETRIC DATA by Barry E. Herchenroder I. INTRODUCTION Regularly spaced bathymetric data are needed by the U.S. Army, Corps of Engineers for input to various numerical models which describe coastal phenom- ena such as storm surge and wave refraction. Bathymetric contours produced from such data are also sometimes needed to help locate important bathymetric features or changes in a project area. To generate regularly spaced bathy- metric data, an adequate set of raw irregularly spaced data must be available and a method to interpolate-extrapolate this data to regularly spaced locations is required. This report describes a large set of bathymetric data available on magnetic tape and products from a computer program which generates regularly spaced data from the raw data; products from a program which generates contours from the regularly spaced data are also described. One source of raw bathymetric data in an area affected by a coastal project may be survey data taken as part of the project. If there are no such data or if the project survey data must be supplemented, a major additional data source is the National Ocean Survey (NOS) digital hydrographic data set available from the National Geophysical and Solar-Terrestrial Data Center (NGSDC) of the National Oceanic and Atmospheric Administration (NOAA). Data from both data sources normally have an irregular spacing. Interpolating-extrapolating irregularly spaced data to regularly spaced locations is onerous when done by hand. Drawing depth or bed elevation con- tours by hand is also time consuming and tedious. To simplify these tasks at the Coastal Engineering Research Center (CERC), two computer programs, ZGRID1 (program No. 72$X6RICG#) and CONTOR (program No. 72@X6R19X) , have been devel- oped or modified. ZGRID1 interpolates or extrapolates and CONTOR determines and draws contours. The two programs are available with documentation from the Engineering Computer Programs Library at U.S. Army Engineer Waterways Experiment Station, Vicksburg, Mississippi. Both ZGRID1 and CONTOR require large, fast computers, e.g., CDC 6699, CDC CYBER176, CRAY-1, IBM 3933, and use standard CALCOMP plotting commands. II. NOS DIGITAL DATA A few years ago, NOS began digitizing U.S. coastal hydrographic data from about 3,200 survey sheets. Most of the resulting digital data have been archived with the NGSDC; they are available on magnetic tape for a fee by writ- ing or phoning National Geophysical and Solar-Terrestrial Data Center, Code D621, EDS/NOAA, Boulder, Colorado 80302, phone (303) 499-1000, extension 6338 (FTS 373-6338). A detailed description of the available digital data, as well as pricing information, is given in National Geophysical and Solar-Terrestrial Data Center (1976, 1979a, 1979b, 1980) and in Lawrence (1977). The digital data are irregularly spaced in latitude and longitude and consist of about 97 percent depth soundings and 3 percent bottom characteristics (e.g., clay, mud , soft, etc.) and dangers to navigation (e.g., wrecks, pilings, etc.) The ‘ls Square areas along the continental United States and Alaskan coasts for which digital data were available as of January 1981 are indicated in Figures 1 and 2. Data from the squares in Figures 1 and 2 were digitized from surveys con- ducted between 1930 and 1965. III. PROGRAM ZGRID1 ZGRID1 is a modification of the program supplied by NGSDC to perform two- dimensional interpolation-extrapolation. Irregularly spaced bathymetry data from the NOS digital tapes or from independently obtained surveys are read by ZGRID1. ZGRID1 then determines the coordinates of each sounding on a map pro- jection preselected by the user and interpolates-extrapolates this data to regularly spaced locations on the projection. As an option of ZGRID1, a plot of the irregularly spaced soundings can be made. Figures 3 and 4 are examples of such plots. Figure 3 shows the sound- ings offshore of Great Egg Harbor Inlet, New Jersey, on a 0.03° (1.8 minute) latitude-longitude square. Soundings were obtained from the NGSDC tape covering the 1° latitude-longitude square 39° to 40° N. latitude, 74° to 75° W. longitude. Figure 4 consists of bed elevations near CERC's Field Research Facility (FRF) at Duck, North Carolina. The FRF bed elevations were derived from a survey made by CERC in September 1978. The estimated bed elevation or sounding value at each regularly spaced loca- tion can be written on a magnetic disk or tape for subsequent use. At the user's discretion, the regularly spaced values can be printed on a lineprinter or plotted. Figure 5 is a plot of the estimated regularly spaced depth values for the same region covered by Figure 3. For this example, there are 30 regu- larly spaced (on the map projection) points in both the x and y directions for a total of 900 regularly spaced points in the whole region. IV. PROGRAM CONTOR CONTOR determines and draws contours of any variable from a two-dimensional array of variable values. These values are assumed to be located at regularly spaced grid points. CONTOR was developed at the Carnegie-Mellon University, Pittsburgh, Pennsylvania, by Robinson and Scarton (1972). When used to contour bed elevation or water depth fields, CONTOR is usually run in conjunction with ZGRID1. ZGRID1 produces the depth or bed elevation values at regularly spaced locations needed by CONTOR. The contours to be plotted are specified by the user. Figures 6 and 7 are examples of contour plots done by CONTOR. Figure 6 corresponds to the region off Great Egg Harbor Inlet covered by Figures 3 and 5. Figure 7 corresponds to the FRF region covered by Figure 4. Figure 6 was produced from the ZGRID1 computed values in Figure 5. Figure 7 was produced from ZGRID1 computed regularly spaced values (not shown) located 82.02 feet (25 meters) apart in both x and y directions. V. LIMITATIONS Limited experience indicates that the data on the NGSDC tapes contain a few gross errors in most 0.25° by 0.25° squares. One satisfactory way to detect these errors is through the use of contour plots. Gross data errors are easily located on these plots since they appear as small "'bull's-eyes." 8 “(0861 ‘te7UeD e}eq TeTAISetAeL -1eyTog pue [eorshydoey [TeucTieN) JASON Woasz odeq uo oTqeTTeAe “ATUO G96T 92 OEET *(4sPoo ueyYseTY 284} FO asouq qdeoxs) elep otydersoipAy 0 (Seete ezenbs ,[) xepuyl “TT ean3sTy 2H == ! i | ey See eet il I Pe j | ! > | | Pel | Square areas) to hydrographic data off the Index (1° Figure 2. available on tape from Alaskan coast, 1930 to 1965 only, NGSDC (National Geophysical and Solar-Terrestrial Data Center, 1980). Ke) -74.500° -74.470° ° * - + + + + + 39,2 a + + + + + + - oore - — ° 5 80 125 128 Ta 39.280 + 12S 13L 131 134 134 131 25 131 134 137, iT] 131 Nae 128 3 134 ast 134 4 137 128 134 134 134 137 t ae 134 134 137 137 Hey i134 138 137 aT 137 134 JL 137 ie 137 137 ] a 134 aaa 137 rag 137 Tt 137 137 140 KO 140 140 oH) 140 140 N Il 137 140 140 140 Maal 140 AL 137 140 140 140 140 137 140 140 140 ia 140 18) 140 140 va 140 143 143 + 143 140 Se 143 143 143 JL 140 143 143 143 143 140 } KG 143 145 140 143 146 143 145 140 143 na 143 143 146 {140 143 a5 aye 145 146 ste 143 148 a T 143 146 14g 146 146 aga 145 if 149 146 149 143 145 148 149 4 146 148 + 143 149 145 143 uO 7 4 143 al 143 143 143 143 19) 14g 145 149 7 | 1s2 149 449 149 149 149 146 i 149 NS2 149 143 152 149 4 152 ‘ 149 tee ae 182 149 T 152 T 152 152 1s2 ee 1439 I 14 | 152 8 a 152 NO) 152 152 182 ke i 152 = Xe 14g 152 4 182 152 152 1sS 182 152 143 143 1665 152 rs 152 182 T 15S 12 1s2 182 152 43, 143 182 1S 1s2 iss 182 182 SS t 146 ‘coe eS TER wwe 182 182 155 180 15S 1PEs lf i 143 152 15S 182 152 182 Y 143 185 1ss 18S 1S8 iss + 143 ty 1ss led SB 158 te be X 4 152 152 1S8 162 1sB ee 1S2 iS 158 pps We 168 158 nES ° 168 18S 1s8 158 39,250 + ——t pr + + + + —182, + — ‘ ' at: + + + : + ee 39.250° -74.500° Figure -74.470° ZGRID1- produced soundings offshore of Great Egg Harbor Inlet, New Jersey, in a 0.03° square area. Axis annotations are N. latitudes (positive numbers) and W. longitudes (negative numbers). Depths are in tenths of meters referenced to MLW. 650,000 475.006 ++ a ee ee eS bon ee “ost ie Si et lt (ON(0)() T ise + az ae mm T 1” m ae 170 109 + ww { ag “7 see a0 ie ney If ves 108 7 ee as? x seo ye ¥ ie 1p iy + + 108 Rea See let) 108 108 00 hee 28 1p + yer ver 4 see see 108 106 108 1s va i + fa 18 ee t a ear T ji ? era I s 18 180 dt 100 ven C 100 ser jez T 1s 160 10080 + + ws 1“ 160 + 160 ee 1 16 ris ry GI ro ieee T ie r Nea 7 ice 107) 18 "7 T a 167 368 17 Aa teal va? 08 1 se + 1a i = 1. yee 8a Ti ice 168 308 ‘ om ne eee 166 set + 160 ul . 18 166 IL I 182 cn yes MEA 18 186 se 1 x - 16 es sof + 8) aD wu irs} 163 see 18 ee er 162 163 T F r T 13 - veo"? 163 oy 169 ne 1a 1 Pe ei 163 "7 Met 160 140 160 il eal 1. veal ae 0 sey a ae fe 100 t a 0 . “a sa + oO ‘ ie Bs , Waite ide 164 = ha XO! ye ae 10 T ay 10 I ery Me ated Maas =) a 1a a BE i 14 0 IL a 10 ur 1 + 7 rome If ri ‘ 1940 a5 - 4 pe ors seat ii om o c wn Lad aoe, 140 + 2 aoe Le! 188 38 as we eae red 130 as ro] + ae op = ry os 1 + 180 am yay BE HE 1 aaa ie 12 1 130 isa | 127 a 130 ate ~ mo) see A A + { an ame mme at aes ta a ye a7 aed ee 1 im dt An ite ue ate "7 Il aa ru jap 1861 ree 326 9 ar ate ate as aa a ae ae wD wy ui} a ae wa 388 DS 420 180 422 = oe te as ra] ane une 1t0 ite ne 07 - ae 7487 ny) ne 10348 ne ne ne ne rr) us ue ue t om a a i es r 0 ry TY Reet ane ane a ui mint ar, no 109 aa us + 100 a a8, iy ty dL 107 1100 a jaa 108 Pet laer) i 110 108 108 x09 it 108 a a 108 108 108 mal 107107 107 107 11 b yo yes ao uz xo 108 108 I i ton 104 o = r 108 104 104 104 04 n a yoo sora 108 100 10 er Pa 101 199 10 _ r ” eal os 100 101 100 j00 i a 4 soe | ” 100 o a ” . ra ov fa dL “ ” ” & os mos qo Po 100 ry ” oa s 1) ord “ i} - tT a » n pa or L) nn ” os Tine o cy el n a Cy ° Lat ” Tr o n D cy o Q oo” oo a O wt o oo o J On ” ea) we eal + AL ” ” ck ow ae 5 4 ry wot a ~ oa os O “ - “ « + IL “ . « a “ mit oo » + “ Q “ e e oo u a o « O ® o ” a on era ides wt n w ~ = er a n ” + n a0 O ” ie iad n”® on n Ww 0 + Le n Ww = ™ " n art ” 73 n IL ” n n™ nn” ™ uw ” T re n n ne a » I ™ n n a nn 7 " * o n nv ™ pe o 70 7” a o wo nn n LS nm if « ” n e oO © Gn oo "% alt “ a a a Gd = C I al Pha) O li e = Q a [we a7 8 et a o [ns an a + a e a 4 D « a + T o o o e Rn _ el. + bd & a. OBIS a a q ao cs oo & nn oa a Tt { a n ao oa fad ° oo a a 2 GG f a « o a o Ae a “ ” ct “ + an < wo ca “a “ I Fr) 2 a « ” » n iL 3 a n a Po = = = a af “ ” 5 I ™ bed a + ol ae q n It « if 1 10 + A = Ip i X F beaten 4} 4 4 : if O ina at +—t—+ + + pAteste Geshe tpt nat i) -925.000 650.000 Figure 4. ZGRIDl-produced bed elevations near CERC's FRF at Duck, North Carolina. The CERC pier has been drawn in by hand. Axis annotations are in meters. Bed elevations are in tenths of meters reference to the 1929 National Geodetic Vertical Datum. Negative elevations are above the datum. 9,280° APS 28,128 _ 2S _, 124, 2S, azn, uaa, za, za, ize, im, ara, 429, aan, ian 27 127° «1270128 AZS STB TB Sa 125 128 «128130132 134 134 138 137 isa ae 146 145 143 150 151 150 182 9,250° -74,500° Figure 5. Figure 3. 13 ASSAY 1p ne yy tp _ipa 14 __ya__paa__ ja 1390-13901) SL DL 1S ASABE ak 92 3Z ASS SD 138 e TSS Ne ae 3 132 19 1SZ SZ SZ_—1SI_ ASE SL wSZ_—ASN. ASS 199 134 ae SS SSS SSSA 137 is iss 33 is ise ise is iss is4 sé iss 134 136 135 iss 196 a37 137 437 18 134194139134 134 13S SSH SE 136137137198 1361369719738 8139 138 ise ise is 1% iss i“ iss 137 ise 138 136 397 1397 i377 137 is 133 139 is 136 is iss ix is 138 138 137 190 139 139 139 190 i” 7 i386 139 199 140 i” i397 136 136 i377 iss 139 140 130 139 139 140 140 140 139 138 139 139 140 140 437 is 138 ise iss 138 140 a4r 140 140 140 140 140 an 440 140 139 140 aan an ise isd 139 130 139 140 wan wan 14n 140 140 wan san waz az wan 140 aan waz 142 140 wan war 140 140 war az 142 142 140 140 war az 143 14a waa 143 waz 143 ag M49 144 A149 4Z AZ 4d 4d 14d 4Z aL eZ ZA dae EMBs 148 1430 taeda na CC Cy Cc CC CC 146 146 45 mid 4s 143 143 14a 14a 144 143 mas 14a 146 146 146 146 146 146 14a 145 145 145 145 146 143 14a 145 146 146 145 145 146 147 0 1466 146 146 146 145 14a 14a 14a 143 145 14a 145 145 46 7 7 147 140 149 149 147 tal y 46 16 146 145 ae 45 laa 145 45 146 146 147 147 140 149 149 149 146 146 146 146 46 147 146 m3 14a 145 1 146 147 147 140 148 149 149 149 146 147 147 147 146 7 147 49 way 146 147 148 140 149 140 148 149 143 149 149 140 47 447 140 ay 147 147 180 149 148 148 1a 180 140 149 140 149 149 149 149 149 1468 146 a7 140 146 148 181 181 149 aa 182 161 149 160 149 149 180 150 149 149 149 140 148 146 140 140 152 162 149 180 162 152 182 162 181 161 161 151 149 149 160 49 149 49 149 14g 182 182 181 181 162 162 182 162 162 162 182 182 181 160 150 160 160 149 160 151 161 162 182 182 162 182 140 161 181 181 182 182 161 160 160 16h 152 182 162 163 150 161 182 152 182 182 182 162 181 4st 182 181 160 160 181 163 164 164 155 165 182 182 182 182 182 162 182 462 1 151 152 182 181 149 181 153 168 165 166 163° 15S BZ 18S 8D HZ HL SZ HS SZ ZZ ABZ ABZ ASDA BESS 187 185 189 166 187 462 162 183 183 163 182 162 183 166 165 186 186 167 ise 166 ise 162 1s 102 186 156 187 182 182 153 164 18s 186 166 187 187 186 Aso, 165, 16h , 185, 15?, 184, 18A, _ifA, As, 18 185 __15p __1Sp__183 _ 144 __1§8 _17___1.2._47__468__458, ZGRID1-produced regularly spaced depth 40 az aa ay a 4s “8 a a7 a cr) 56 87 »39.250° —74.470° values for the same area off of Great Egg Harbor Inlet, New Jersey, covered by Depths are in tenths of meters referenced to MLW. V X *sJojoW UT o1e SeNTeA ANORVUOD “Fy 2ANBTY hq peteaod Yd S,OWAD Teeu uotT3e1 owes ay 1OF sanojuod yjdep peonpoird-YOLNOD °Z2 9an3ty *siojoll UT Ve SaNTeA ANoOjUOD *¢ pue ¢ sein8tq Aq peteaod ‘Aosier MeN *jJaTUl Aoqiey .ee1H FO FJO eore owes ay. 1IOF sanoquods yjdep pednpord-yYOINOD °g o1in3Ty 14 1. ZGRIDI1. ZGRID1 sometimes gives poor results near a land-water boundary or an outer computational boundary where there are too few irregularly spaced raw data points. Where there is a significant topographic trend, ZGRID1 can also give misleading results if the number of raw data points is too small. 2. CONTOR. When a bathymetric feature has a size comparable to the grid spacing, con- tours which go near or through the feature may cross or have unrealistic loops or wiggles. To minimize this contour "noise," the regularly spaced depth or bed elevations produced by ZGRID1 may have to be smoothed. VI. SUMMARY This report gives general descriptions of products from two computer pro- grams (ZGRID1 and CONTOR) which process digital bathymetric data. ZGRID1 gen- erates regularly spaced bathymetric data from irregularly spaced data, and CONTOR uses regularly spaced data to determine and draw contours. A large set of bathymetric data available on magnetic tape for U.S. coastal regions is also described. Examples of program output are presented for two areas, one near Great Egg Harbor Inlet and the other near CERC's FRF. LITERATURE CITED LAWRENCE, C., "Catalog of Digital Bathymetric Data for the United States Coastal Regions, 34°-45° North Latitude, Atlantic Coast," National Geo- physical and Solar-Terrestrial Data Center, Boulder, Colo., Apr. 1977. NATIONAL GEOPHYSICAL AND SOLAR-TERRESTRIAL DATA CENTER, Flier 1976 (V), Boulder, Colo., 1976. NATIONAL GEOPHYSICAL AND SOLAR-TERRESTRIAL DATA CENTER, Flier 1979 (Q), Boulder, Colo., 1979a. NATIONAL GEOPHYSICAL AND SOLAR-TERRESTRIAL DATA CENTER, Flier 1979 (W), Boulder, Colo., 1979b. NATIONAL GEOPHYSICAL AND SOLAR-TERRESTRIAL DATA CENTER, Flier 1980 (SE-F), Boulder, Colo., 1980. ROBINSON, E.L., Jr., and SCARTON, H.A., "CONTOR: A Fortran Subroutine to Plot Contours of a Single-Valued Arbitrary Three-Dimensional Surface," Journal of Computational Phystes, Vol. 10, 1972, pp. 242-251. 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