About the Rennerian Coordinate Calculator

// =================================================================== // Gazza's Great Circle Calculator // Author: Gary Nicholson // WWW: http://www.gazza.co.nz/ // // ** bastardized by: Brian Levetzow for HBD // // NOTICE: You may use this code for any purpose, commercial or // private, without any further permission from the author. You may // remove this notice from your final code if you wish, however it is // appreciated by the author if at least my web site address is kept. // // Let me know if you use this on your site and I may link to your site. // // You may *NOT* re-distribute this code in any way except through its // use. That means, you can include it in your product, or your web // site, or any other form where the code is actually being used. You // may not put the plain javascript up on your site for download or // include it in your javascript libraries for download. Instead, // please just point to my URL to ensure the most up-to-date versions // of the files. Thanks. // // Permission to use this code without asking first may not apply // to other calculators on my site. If in doubt ask me first. // // ** Edited and reused with permission - Brian Levetzow // ** Reuse limited to generating "Rennerian Coordinates" for members of HBD. // ** Several items were significantly modified from the original code. // // =================================================================== var pi = Math.PI; var secsize = 4; // round second display to var distsize = 1; // round distance display to var bearsize = 1; // round bearing display to var tol = 0.000000000000001; function about(){ var w = window.open("", "aboutwin", 'toolbar=0,location=1,directories=0,status=1,menubar=0,scrollbars=1,resizable=1,width=600,height=500'); var d = w.document; d.open(); d.writeln("\n\nAbout the Rennerian Coordinate Calculator"); d.writeln("\n\n"); d.writeln("

About the Rennerian Coordinate Calculator

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The HBD collective thanks Gary Nicholson for allowing modification to his original code for HBD cameraderie. Brian Levetzow."); d.writeln("

The lat/lon coordinates can be entered in decimal degrees in the degree field. The results are rounded to better fit the [0,0] coordinate 'standard'."); d.writeln("

Thanks to Ed Williams for the original formulae used here. The user accepts sole responsibility for the use and results of this calculator."); d.writeln("

The convention I use on all my calculators is Positive for East and North, Negative for South and West."); d.writeln("

If you find any errors or have any suggestions to make about this calculator send me an email.

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Gary Nicholson, 10 June 2001.

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"); d.writeln("\n"); d.close(); return true; } function huh(){ var w = window.open("", "aboutwin", 'toolbar=0,location=1,directories=0,status=1,menubar=0,scrollbars=1,resizable=1,width=600,height=500'); var d = w.document; d.open(); d.writeln("\nWhat are my Geo-coordinates?"); d.writeln(""); d.writeln("

What are my Geo-coordinates?

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Here are just a few ways for you to generate your Geographic coordinates:"); d.writeln("

--Use a GPS receiver (O.K., THAT was obvious)"); d.writeln("

--Go to Yahoo Maps and map your address. Then zoom into the highest magnification."); d.writeln("Your Geo-coordinates will appear in the URL line in decimal degree form. The info you're looking for will look like this:"); d.writeln("

Yahoo format = &slt=39.132400&sln=-76.840800"); d.writeln("

--Go to the Census Bureau Gazetteer and use your ZIP code as a starting point. You can then browse the Tiger Map, refine your location, and your coordinates will appear below the Tiger Map."); d.writeln("

You can enter any of these decimal numbers directly into the latitude and longitude Degree fields (minutes and seconds not needed if using the decimal format). "); d.writeln("

--Please share other ideas by posting in HBD."); d.writeln("

"); d.writeln(""); d.close(); return true; } function deg2rad(x){ //convert decimal degrees to radians x = x * pi / 180; return x; } function rad2deg(x){ //convert radians to decimal degrees x = x * 180 / pi; return x; } function roundoff(x,y){ //round off x to y decimal places x = parseFloat(x); y = parseFloat(y); x = Math.round(x * Math.pow(10,y))/Math.pow(10,y); return x; } function mod(x,y){ return x-y*Math.floor(x/y); } function modlon(x){ //ensure longitude is +/-180 return mod(x+pi,2*pi)-pi; } function modcrs(x){ //ensure course is 0-360 return mod(x,2*pi); } function modlat(x){ //ensure latitude is +/-90 return mod(x+pi/2,2*pi)-pi/2; } function dms2ddd(d,m,s){ if (isblank(d)) d = '0'; else { var y = d.slice(0, 1); d = parseFloat(d); } if (isblank(m)) m = '0'; else m = parseFloat(m); if (isblank(s)) s = '0'; else s = parseFloat(s); var x = Math.abs(d) + (Math.abs(m) / 60) + (Math.abs(s) / 3600); //convert to decimal degrees if ((y == "-") || (d < 0) || (m < 0) || (s < 0)) x = -x; return x; } function isblank(s) { for(var i = 0; i < s.length; i++) { var c = s.charAt(i); if ((c != ' ') && (c != '\n') && (c != '\t')) return false; } return true; } //function calcRandBgc(form, in1, in2, in3, in4, in5, in6){ //calculate great circle distance and course function calcRandBgc(form, in1, in2, in3, in4, in5){ //calculate great circle distance and course // in1 - point 1 latitude index // in2 - point 1 longitude index // in3 - point 2 latitude index // in4 - point 2 longitude index // in5 - distance index // in6 - bearing index var j = form.units.selectedIndex; var units = form.units.options[j].value; var latddd1 = dms2ddd(form.degreevalue[in1].value, form.minutevalue[in1].value, form.secondvalue[in1].value); // convert latitude of point to decimal degrees then radians var latrad1 = deg2rad(latddd1); var londdd1 = dms2ddd(form.degreevalue[in2].value, form.minutevalue[in2].value, form.secondvalue[in2].value); // likewise for longitude var lonrad1 = deg2rad(londdd1); var latddd2 = dms2ddd(form.degreevalue[in3].value, form.minutevalue[in3].value, form.secondvalue[in3].value); // convert latitude of point to decimal degrees then radians var latrad2 = deg2rad(latddd2); var londdd2 = dms2ddd(form.degreevalue[in4].value, form.minutevalue[in4].value, form.secondvalue[in4].value); // likewise for longitude var lonrad2 = deg2rad(londdd2); var w = lonrad2 - lonrad1; var v = latrad1 - latrad2; var s = 2 * Math.asin(Math.sqrt((Math.sin(v / 2) * Math.sin(v / 2)) + (Math.cos(latrad1) * Math.cos(latrad2) * Math.sin(w / 2) * Math.sin(w / 2)))); if (Math.cos(latrad1) < tol){ //initial point is pole if (latrad1 > 0){ //start from north pole var x = pi; } else { //start from south pole var x = 0; } } else { //initial point isn't on pole if (Math.sin(lonrad1 - lonrad2) < 0){ var x = Math.acos((Math.sin(latrad2) - Math.sin(latrad1) * Math.cos(s)) / (Math.sin(s) * Math.cos(latrad1))); } else { var x = 2 * pi - Math.acos((Math.sin(latrad2) - Math.sin(latrad1) * Math.cos(s)) / (Math.sin(s) * Math.cos(latrad1))); } } s = (s * 180 * 60 * 1852) / pi; // answer in metres form.distvalue.value = roundoff((s / units), distsize); //round off distance and convert to selected units if (w == 0) { if (latddd2 < latddd1) x = pi; else if (latddd2 > latddd1) x = 0; else if (latddd2 == latddd1) { x = 0; form.distvalue.value = roundoff(0, distsize); //round off distance } } var bearing = rad2deg(x); bearing = roundoff(bearing,bearsize); form.distvalue.value = "[" + form.distvalue.value + ", " + bearing +"deg] AR"; return true; } function dddround(form, ind, bearing){ var y = Math.abs(parseFloat(bearing)); y = roundoff(y,bearsize); // round off decimal bearing form.degreevalue[ind].value = y; form.degreevalue[ind].value += "\260"; // add the degree sign to the end return true; }