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scan0055 - The first job is to make each nibble(hex digit...

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Unformatted text preview: The first job is to make each nibble (hex digit) lovingly visible. So execute on rohan the command od —x MOCities.shp, and do the same with the .dbf and .shx files. The 'od' stands for 'octal dump', and the x option gives you a hex dump. If your checkered background makes hex dumps seems unreadable, find a more knowing partner to help you get going. Each person is to do his/her own work, but getting a couple of boosts is ok. DO NOT WORK TOGETHER. NOW you need to save the outputs. On rohan you can 'redirect' output from the screen to a file by using (f¥> 'to', written as > E.g. od —x MOCities.shp > od.shp 'X\ .2!— \_/ Do this for .shp and .dbf also. The next step is to create more space in these file, e.g. by triple spacing the lines, so you can make notes all over the dump files. The goal is to show you know the internal formats of the .shp and .shx files intimately by annotating their hex dumps byte by bitter byte. Much of the data (the coordinates of the points) is in IEEE floating point format. You should know this already of course from an assembler language class, but if not try google, or your buddy George for help, or the instructor. Knowing the answer from the MOCities.txt file will help you check your floating point decoding. Show CAREFULLY how to decode one of the floating point numbers, i.e. how to figure out some latitude or longitude if all the world gave you was a hex dump. Another issue (obstacle) is that some values are big endian, and others are little endian. Google is a good place to start for this as well if are not already in tune to the endians. ($0 0L) tb3c<g t. As a gut check, here is the .shp file you should probably have after the ‘ hex dump: -[ 'A 00% WW“ GD ‘ /' H301 0 f L J _ 0000000 0000 50a 0000 0000 0000 00 0000 0000 * VO/ywn L, 1r m yr . 0000020 0000 0000 0900 0000 5000010 6 e803 0000 / 0000040 0100 OOCOIigae 47elm1ab4nilcd 5C§E c2f5 0000060 289C 4240 52b8 le85 eb6l 56c0 3d0a d7a3 0000100 70dd 4340 0000 0000 0000 0000 0000 0000 ® 0000120 0000 0000 0 00 0000 0000 0000 0000 0000 \ to y > C) 4 mm? (N4 ~~ / ‘W' 0000140 0000 0000|‘0” 00 0001 0000 000a 0100 0000 Won ‘ ' ~ ” ,, 0000160 3333 3333 353'5’7c0 5c8f c2f5 209c 4240 7 WM" 0000200 0000 0002 0000 000a‘0100 000‘0 cdcc cccc - ‘1 0000220 cc0'c' §7dq;cdc\c"c’c'cc cc4c 4340 0000 0003 ”NW“ WWW“! 7"”?7’ ,1 0000240 0000 000a“ 0100 0000 cdcc cccc cc8c 50c0 of ,4 0000260 713d Oad7 a350 4340 0000 0004 0000 000a mi) f" 0000300 0100 0000 85eb Slb8 1’ea’5’57’c‘0 0ad7 a370 .. v ry 0000320 3d8a 4340 0000 00115 0000 0003‘ 0100 0000 f0 0000340 l4ae 47el 724104 .57ch 3dOa d7a3 70dd 4340 3 0000360 0000 0000 00007000a10100 0000 52130 le85 (J 0 0000400 eb6l "56c0 a470 3d0a d7a3 4240 (30 0000414 After getting the hex dump files, you should triple space them so you have plenty of room to highlight, underscore, and explain each group of nibbles. 0525: '5 7 \ o 7 1 ° 0 ,‘ 37d6f \Axuu— say-‘6 742 +129 +? i 99 2+2=l<3°° ...
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