Custom Map Databases and Map Overlays "Maps and Legends, The Cartographer", version 2.0 includes a feature to let you create and use additional map coordinate files. The "Overlay..." option of the "Files" menu allows you to select and draw maps from files you can create. In this section the format of these files is described together with examples of how to use the "create.ttp" utility to generate additional map coordinate databases. The "Overlay" feature is very general. With it you can draw almost anything on your maps, including roads, cities, country boundaries, time zones, or satellite ground tracks, in any of the available projections. The "Overlay..." option under the menu item "Files" is enabled whenever you draw a map in any of the "Maps and Legends" projections. If you select this option, the "file selector" will appear showing you the directory of all files with the ".INT" extension in the "DAT" folder of the program disk. Selecting one of these files and clicking on the "OK" button will load and draw it according to the projection and scale of the map drawn most recently. You can use the file selector to search other folders or even other disks by clicking on a folder, clicking on the close button of the directory window, or by editing the pathname above the directory window. When you have selected the file you wish to plot, just click on the OK button. Any number of overlay files may be added to any map, using different line widths or pen colors, as desired. Format of the ".INT" file. A point on a map is described by latitude and longitude. In addition, if you want to describe boundaries or paths between points you need to specify whether or not to draw a line to this point from the previous one. Together, these three pieces of information, whether or not to connect, latitude, and longitude, form one coordinate set in the "Maps and Legends" data files (".INT" files). In this section, we describe the format of the ".INT" file for the benefit of those who wish to generate their own files from other databases. In "Maps and Legends", map position items are stored on the disk as an array of integers organized as {(Connect?) (10 * longitude) (10 * colatitude)} Points are plotted in the order that they appear in the file. The first integer of every coordinate set, "Connect?", is either zero or one, and specifies whether or not to draw a line to this point from the previous one according to the Page 30 code 0 = NO, 1 = YES. The second item of each set, "10 * longitude" is an integer which is ten times the east longitude of the point. It must have a value in the range from 0 to 3600. The last item, "10 * colatitude" is an integer in the range 0 to 1800. Its value is 10 times the colatitude of the point. Colatitude is like latitude, but is measured from the North Pole. The colatitude of the equator is 90 degrees and the south pole is at 180 degrees colatitude. The maximum allowed size of any ".INT" file is 12000 bytes. This is enough room for 2000 sets of coordinates, each set consisting of these three integers (2 bytes per integer). A ".INT" file may be as small as one coordinate set (6 bytes). The "CREATE.TTP" Utility While the ".INT" file format is a convenient one for the computer, it is not so convenient for people. The "CREATE.TTP" utility is included with "Maps and Legends", version 2.0, to provide a way to generate coordinate data files quickly and easily from an ASCII file. With the help of "CREATE" you can use any word processor or text editor to enter coordinate sets for "Maps and Legends" to draw. "CREATE" takes as input an ASCII file and creates a ".INT" file from it. The format of the ASCII file for "CREATE" is flexible. The file should contain lists of numbers in the order: CONNCT?1 LATITD1 LONGITD1 CONNCT?2 LATITD2 LONGITD2 where CONNCT? has the same definition as CONNECT? in the ".INT" file, LATITD and LONGITD are the latitude (not colatitude) and longitude of the point. The only other requirement on the format of the file is that no numeric ASCII character can appear in it unless that numeric is part of some "CONNCT? LATITD LONGITD" set. Consecutive values can be separated by any number (at least one) of any characters except numerics (and single decimal points). "CREATE.TTP" does some simple consistency checking as it processes its input file to detect any major format or range errors. For example, if the value of CONNCT? is something other than 0 or 1 (".0" or "1.000000", etc. are also permitted), an error message will appear. You must correct the error before the rest of the file can be processed by "CREATE". Latitude and longitude can be given as positive (north latitude, east longitude) or negative (south latitude, west longitude) numbers with or without decimal points. Latitude should be in the range from -90 degrees (south pole) to 90 degrees (north pole). Longitude should be in the range from -180 degrees to 360 degrees. West longitudes can have values less than 0 or more than 180, whichever you prefer. Decimal values will be rounded to the nearest 0.1 degrees. Page 31 You can include any comments or other labels in the file as long as they do not contain any numeric characters. Below are some examples of text files acceptable to "CREATE" which describe the border of the state of Wyoming. Example A This draws the Wyoming state border. 0 45 -111.05 1 45 -104.05 1 41 -104.05 1 41 -111.05 1 45 -111.05 Example B This also draws the Wyoming state border. 0,45.00,-111.05 Northwest 1,+45. ,-104.05 Northeast 1+41-104.05+1+41-111.05 Southern border 1 45.0000000000 -111.05 Wyoming complete ! To run "CREATE", double click on the file "CREATE.TTP". When the parameter dialog appears, enter the name of the ACSII text file that you wish to process and click on "OK" or press return. The program will list each coordinate set as it is processed. The diagnostic messages are self-explanatory. The output file made by "CREATE" will have the same name as the input file, but with the ".INT" extension. It is unwise to use ".INT" as the file name extension of the text input file. Once created, the ".INT" file is ready to be used with the "Overlay..." option. As an example, to help you to get started, we have included the file "ORBIT.TXT", a sample ASCII text file containing hourly position coordinates for the ground track of a high altitude satellite (SCATHA) over a two day period. Run "CREATE.TTP" on it to create "ORBIT.INT". The ground track is a series of loops over the equator (near Central America for this period) that move east by about 5 degrees per day. Special Note: The earth is round, and there are many different ways to draw "straight lines" between two points on the earth, depending on the projection you choose. When drawing a map, the program does some checking to see whether it is drawing the "shortest" line. As a result, if you want to draw a path between two widely spaced positions, you may find it necessary to include some intermediate "waypoints" to get the line drawn the way you want it. Page 32