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etopo5b.doc
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1989-03-24
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GEOPHYSICS OF NORTH AMERICA etopo5b.doc
- 5 MINUTE TOPOGRAPHY/BATHYMETRY CONTOURS
This directory contains the contours of the 5 minute topography and
bathymetry data set.
In order to understand how the data are arranged, one must understand
something about the process of generating these data. The contouring was
done in 100 regions each 15 by 15 degrees. Each contiguous section of each
contour line is called a segment and each segment is made up of some number
of line fragments. Each segment starts with an implicit move command and
the fragments are the endpoints of a series of draw commands. The data
storage scheme therefore has three basic units: regions, segments, and
points (where points are the ends of fragments).
The regionalization of the data is expressed in the file structure. The
data are stored in 72 files, each called ETOPO5.NUM, where NUM is the region
number. Each data file has the longitude and latitude pairs of the
endpoints of the contour lines for all of the contours within the given
region. These values are stored in two 4-byte floating point numbers.
Parameters for ETOPO5 Contour Regions:
Region Minimum Minimum Maximum Maximum Number of Number of
Longitude Latitude Longitude Latitude Segments Points
0 170 75.083 184.917 89.674 58 9050
1 170 60.083 184.917 75.167 242 9463
2 170 45.083 184.917 60.167 523 28953
3 170 30.083 184.917 45.167 937 29778
4 170 15.083 184.917 30.167 1419 33312
5 170 0.083 184.917 15.167 993 24397
6 184.833 75.083 199.917 89.821 81 12537
7 184.833 60.083 199.917 75.167 166 4925
8 184.833 45.083 199.917 60.167 340 19195
9 184.833 30.083 199.917 45.167 782 16017
10 184.833 15.083 199.917 30.167 1569 39950
11 184.833 0.083 199.917 15.167 1608 30427
12 199.833 75.083 214.917 89.866 72 10786
13 199.833 60.083 214.917 75.167 553 19750
14 199.833 45.083 214.917 60.167 709 19572
15 199.833 30.083 214.917 45.167 950 15433
16 199.833 15.083 214.917 30.167 1313 25058
17 199.833 0.083 214.917 15.167 1123 20232
18 214.833 75.083 229.917 89.866 49 6937
19 214.833 60.083 229.917 75.167 746 20892
20 214.833 45.083 229.917 60.167 1564 28256
21 214.833 30.083 229.917 45.167 1406 20005
22 214.833 15.083 229.917 30.167 1005 15816
23 214.833 0.083 229.917 15.167 406 7947
24 229.833 75.083 244.917 89.833 76 12642
25 229.833 60.083 244.917 75.167 608 13877
26 229.833 45.083 244.917 60.167 2748 45774
27 229.833 30.083 244.917 45.167 1872 38753
28 229.833 15.083 244.917 30.167 1489 22037
29 229.833 0.083 244.917 15.167 474 8678
30 244.833 75.083 259.917 89.926 106 11038
31 244.833 60.083 259.917 75.167 159 5634
32 244.833 45.083 259.917 60.167 548 11254
33 244.833 30.083 259.917 45.167 1314 30710
34 244.833 15.083 259.917 30.167 2032 43493
35 244.833 0.083 259.917 15.167 846 14853
36 259.833 75.083 274.917 89.955 215 15071
37 259.833 60.083 274.917 75.167 220 6923
38 259.833 45.083 274.917 60.167 120 3383
39 259.833 30.083 274.917 45.167 198 4804
40 259.833 15.083 274.917 30.167 832 30647
41 259.833 0.083 274.917 15.167 988 24543
42 274.833 75.083 289.917 89.962 321 22769
43 274.833 60.083 289.917 75.167 408 12129
44 274.833 45.083 289.917 60.167 280 5756
45 274.833 30.083 289.917 45.167 337 12307
46 274.833 15.083 289.917 30.167 1100 45348
47 274.833 0.083 289.917 15.167 1039 38914
48 289.833 75.083 304.917 89.961 172 15964
49 289.833 60.083 304.917 75.167 421 16172
50 289.833 45.083 304.917 60.167 581 13936
51 289.833 30.083 304.917 45.167 749 19516
52 289.833 15.083 304.917 30.167 941 29602
53 289.833 0.083 304.917 15.167 504 21259
54 304.833 75.083 319.917 89.929 90 11163
55 304.833 60.083 319.917 75.167 701 19842
56 304.833 45.083 319.917 60.167 265 13996
57 304.833 30.083 319.917 45.167 1226 26121
58 304.833 15.083 319.917 30.167 2106 42257
59 304.833 0.083 319.917 15.167 788 22293
60 319.833 75.083 334.917 89.698 110 11292
61 319.833 60.083 334.917 75.167 330 17288
62 319.833 45.083 334.917 60.167 979 21708
63 319.833 30.083 334.917 45.167 1510 31812
64 319.833 15.083 334.917 30.167 1678 30754
65 319.833 0.083 334.917 15.167 1372 29441
66 334.833 75.083 349.917 89.289 177 13894
67 334.833 60.083 349.917 75.167 570 20739
68 334.833 45.083 349.917 60.167 503 20608
69 334.833 30.083 349.917 45.167 1076 32388
70 334.833 15.083 349.917 30.167 451 16682
71 334.833 0.083 349.917 15.167 573 19404
The index file (ETOPO5.INX) contains information about the segments. There
is one 20 byte record for each segment. Each record contains the contour
level for the segment (2 byte integer), the minimum longitude (degrees
east), minimum latitude, maximum longitude (degrees east), maximum latitude
of the box surrounding the segment (each a 4 byte floating point number),
and the number of points in the segment (2 byte integer). The relationship
between the index file and the data files is known through the byte offset
to the beginning of each data set in the index file. These byte offsets can
be calculated from the number of segments in each data set (20 * cumulative
number of segments).
The contour level is a relative value related to the actual data value and
contour interval as follows:
Contour interval = 200 meters
First contour level = 1 Contour data value = -8200 meters
Zero contour level = 42 Contour data value = 0 meters
Maximum contour level = 66 Contour data value = 4800 meters
These are the offsets in bytes to the first segment of
each region in the ETOPO5 contour index file:
Reg Offset Reg Offset Reg Offset Reg Offset Reg Offset
0 0 1 1160 2 6000 3 16460 4 35200
5 63580 6 83440 7 85060 8 88380 9 95180
10 110820 11 142200 12 174360 13 175800 14 186860
15 201040 16 220040 17 246300 18 268760 19 269740
20 284660 21 315940 22 344060 23 364160 24 372280
25 373800 26 385960 27 440920 28 478360 29 508140
30 517620 31 519740 32 522920 33 533880 34 560160
35 600800 36 617720 37 622020 38 626420 39 628820
40 632780 41 649420 42 669180 43 675600 44 683760
45 689360 46 696100 47 718100 48 738880 49 742320
50 750740 51 762360 52 777340 53 796160 54 806240
55 808040 56 822060 57 827360 58 851880 59 894000
60 909760 61 911960 62 918560 63 938140 64 968340
65 1001900 66 1029340 67 1032880 68 1044280 69 1054340
70 1075860 71 1084880
The region parameters and the byte offsets are contained in the file
contour.h which is on your program disk.
The programs listindx and listdata (on the accompanying diskette) read the
index and data files respectively and output the contents to standard output
as ASCII.