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1989-03-24
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GEOPHYSICS OF NORTH AMERICA - DNAG MAGNETICS CONTOURS dmag.doc
This directory contains the contours of the DNAG magnetics 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 133 regions. 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 is stored in 133 files, each called DMAG.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 Magnetic Regions:
Region Minimum Minimum Maximum Maximum Number of Number of
Longitude Latitude Longitude Latitude Segments Points
0 170.037 50.911 179.000 53.500 196 2232
1 170.041 53.500 179.000 62.417 270 7747
2 170.037 62.417 179.000 70.292 711 26020
3 179.000 49.078 188.000 53.500 521 9621
4 179.000 53.500 188.000 62.417 374 9187
5 179.000 62.417 188.000 69.130 523 18772
6 188.000 45.246 197.000 53.500 1430 19388
7 188.000 53.500 197.000 62.417 825 18817
8 188.000 62.417 197.000 71.333 410 8418
9 191.000 71.333 197.000 80.149 76 1975
10 198.458 39.120 206.000 44.583 818 4393
11 197.000 44.583 206.000 53.500 3387 29242
12 197.000 53.500 206.000 62.417 1176 20565
13 197.000 62.417 206.000 71.333 1077 23058
14 197.000 71.333 206.000 80.214 702 9202
15 209.537 28.167 215.000 35.667 1414 3336
16 206.000 35.667 215.000 44.583 600 3012
17 206.000 44.583 215.000 53.500 1245 6723
18 206.000 53.500 215.000 62.417 1717 22733
19 206.000 62.417 215.000 71.333 1110 20689
20 206.000 71.333 215.000 80.212 1288 9624
21 220.412 5.875 224.000 8.917 212 328
22 218.620 8.917 224.000 17.833 719 1507
23 215.833 17.833 224.000 26.750 1587 4284
24 215.000 26.750 224.000 35.667 2620 9583
25 215.000 35.667 224.000 44.583 1766 17198
26 215.000 44.583 224.000 53.500 1969 25438
27 215.000 53.500 224.000 62.417 2495 28437
28 215.000 62.417 224.000 71.333 907 14965
29 215.000 71.333 224.000 80.213 729 5590
30 224.000 6.167 233.000 8.917 241 601
31 224.000 8.917 233.000 17.833 576 1649
32 224.000 17.833 233.000 26.750 2735 7831
33 224.000 26.750 233.000 35.667 2935 12853
34 224.000 35.667 233.000 44.583 3155 41095
35 224.000 44.583 233.000 53.500 3175 60822
36 224.000 53.500 233.000 62.417 2349 35583
37 224.000 62.417 233.000 71.333 359 7312
38 224.000 71.333 233.000 80.214 294 8487
39 233.000 6.875 242.000 8.917 219 683
40 233.000 8.917 242.000 17.833 624 1982
41 233.000 17.833 242.000 26.750 2305 8813
42 233.000 26.750 242.000 35.667 2926 27645
43 233.000 35.667 242.000 44.583 2421 51096
44 233.000 44.583 242.000 53.500 2507 43313
45 233.000 53.500 242.000 62.417 1372 27598
46 233.000 62.417 242.000 71.333 520 11073
47 233.000 71.333 242.000 80.214 182 7523
48 242.000 7.000 251.000 8.917 460 1527
49 242.000 8.917 251.000 17.833 3473 12798
50 242.000 17.833 251.000 26.750 4599 26568
51 242.000 26.750 251.000 35.667 2023 29333
52 242.000 35.667 251.000 44.583 1897 39788
53 242.000 44.583 251.000 53.500 1513 30534
54 242.000 53.500 251.000 62.417 2087 49100
55 242.000 62.417 251.000 71.167 1917 32685
56 242.000 72.500 251.000 80.212 110 3690
57 251.000 7.292 260.000 8.917 810 3802
58 251.000 8.917 260.000 17.833 6241 27950
59 251.000 17.833 258.109 25.464 1885 13858
60 251.000 27.995 260.000 35.667 1043 24498
61 251.000 35.667 260.000 44.583 1671 42759
62 251.000 44.583 260.000 53.500 988 24172
63 251.000 53.500 260.000 62.417 4333 76859
64 251.000 62.417 260.000 71.333 2594 51626
65 251.000 71.333 260.000 80.213 210 5067
66 260.000 7.250 269.000 8.917 506 2147
67 260.000 8.917 269.000 16.625 1186 16681
68 261.024 18.542 269.000 26.750 65 2312
69 260.000 26.750 269.000 35.667 613 18610
70 260.000 35.667 269.000 44.583 2140 55767
71 260.000 44.583 269.000 53.500 3695 68234
72 260.000 53.500 269.000 62.417 4878 84882
73 260.000 62.417 269.000 71.333 2354 44292
74 260.000 71.333 269.000 80.213 375 8098
75 269.000 6.995 278.000 8.917 974 5757
76 269.000 8.917 278.000 17.833 1561 7844
77 269.000 17.833 278.000 26.750 319 9899
78 269.000 26.750 278.000 35.667 832 24649
79 269.000 35.667 278.000 44.583 1939 52903
80 269.000 44.583 278.000 53.500 4010 67878
81 269.000 53.500 278.000 62.417 2660 58934
82 269.000 62.417 278.000 70.083 2020 29983
83 269.000 71.995 278.000 80.213 613 18445
84 278.000 6.833 283.421 8.917 190 1827
85 278.000 8.917 287.000 17.833 467 16174
86 278.000 17.833 287.000 26.750 971 18687
87 278.000 26.750 287.000 35.667 1592 24663
88 278.000 35.667 287.000 44.583 2760 51170
89 278.000 44.583 287.000 53.500 5339 76943
90 278.000 53.500 287.000 62.417 4627 82922
91 278.000 62.417 287.000 71.333 1318 19022
92 278.000 71.333 287.000 80.213 619 13633
93 289.208 7.997 296.000 8.917 58 1202
94 287.000 8.917 296.000 17.833 397 10939
95 287.000 17.833 296.000 26.750 3405 19908
96 287.000 26.750 296.000 35.667 2144 22429
97 287.000 35.667 296.000 44.583 1010 24342
98 287.000 44.583 296.000 53.500 5897 90660
99 287.000 53.500 296.000 62.417 4881 81251
100 287.000 62.417 296.000 71.333 1261 20089
101 287.000 71.333 296.000 80.208 284 12682
102 296.000 8.042 300.380 8.917 69 1094
103 296.000 8.917 302.417 17.833 442 9863
104 296.000 17.833 305.000 26.750 4277 13234
105 296.000 26.750 305.000 35.667 3887 22833
106 296.000 35.667 305.000 44.583 1070 19745
107 296.000 44.583 305.000 53.500 5499 87069
108 296.000 53.500 305.000 62.417 2021 41625
109 296.000 62.417 305.000 71.333 625 18716
110 296.000 71.333 304.542 76.125 166 8282
111 305.000 24.867 305.963 26.750 84 149
112 305.000 26.750 310.750 35.667 941 3093
113 305.000 35.667 314.000 44.583 1025 24037
114 305.000 44.583 314.000 53.500 665 23519
115 305.000 53.500 314.000 62.417 452 18306
116 305.000 62.417 314.000 70.966 357 9632
117 314.000 37.458 323.000 44.583 463 5930
118 314.000 44.583 323.000 53.500 1078 17450
119 314.000 53.500 323.000 62.417 1491 20204
120 314.000 62.417 323.000 68.005 393 9936
121 323.000 43.917 323.000 43.921 10 10
122 323.000 45.333 332.000 53.500 1625 10313
123 323.000 53.500 332.000 62.417 2874 35829
124 323.000 62.417 332.000 68.500 1743 27657
125 332.000 47.625 341.000 53.500 498 14376
126 332.000 53.500 341.000 62.417 1759 56927
127 332.000 62.417 341.000 71.333 2539 44606
128 334.333 71.333 341.000 79.583 192 7132
129 341.000 49.500 349.005 53.500 188 7920
130 341.000 53.500 349.958 62.417 858 27169
131 341.000 62.417 349.958 71.333 2988 65073
132 341.000 71.333 349.375 79.588 477 15649
The index file (DMAG.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 = 100 nanoTesslas
First contour level = 1 Contour data value = -1200 nanoTesslas
Zero contour level = 13 Contour data value = 0 nanoTesslas
Maximum contour level = 31 Contour data value = 1800 nanoTesslas
These are the offsets in bytes to the first segment of
each region in the Magnetic contour index file:
Reg Offset Reg Offset Reg Offset Reg Offset Reg Offset
0 0 1 3920 2 9320 3 23540 4 33960
5 41440 6 51900 7 80500 8 97000 9 105200
10 106720 11 123080 12 190820 13 214340 14 235880
15 249920 16 278200 17 290200 18 315100 19 349440
20 371640 21 397400 22 401640 23 416020 24 447760
25 500160 26 535480 27 574860 28 624760 29 642900
30 657480 31 662300 32 673820 33 728520 34 787220
35 850320 36 913820 37 960800 38 967980 39 973860
40 978240 41 990720 42 1036820 43 1095340 44 1143760
45 1193900 46 1221340 47 1231740 48 1235380 49 1244580
50 1314040 51 1406020 52 1446480 53 1484420 54 1514680
55 1556420 56 1594760 57 1596960 58 1613160 59 1737980
60 1775680 61 1796540 62 1829960 63 1849720 64 1936380
65 1988260 66 1992460 67 2002580 68 2026300 69 2027600
70 2039860 71 2082660 72 2156560 73 2254120 74 2301200
75 2308700 76 2328180 77 2359400 78 2365780 79 2382420
80 2421200 81 2501400 82 2554600 83 2595000 84 2607260
85 2611060 86 2620400 87 2639820 88 2671660 89 2726860
90 2833640 91 2926180 92 2952540 93 2964920 94 2966080
95 2974020 96 3042120 97 3085000 98 3105200 99 3223140
100 3320760 101 3345980 102 3351660 103 3353040 104 3361880
105 3447420 106 3525160 107 3546560 108 3656540 109 3696960
110 3709460 111 3712780 112 3714460 113 3733280 114 3753780
115 3767080 116 3776120 117 3783260 118 3792520 119 3814080
120 3843900 121 3851760 122 3851960 123 3884460 124 3941940
125 3976800 126 3986760 127 4021940 128 4072720 129 4076560
130 4080320 131 4097480 132 4157240
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 read the index and data files
respectively and output the contents to standard output as ASCII.