Latitude, Longitude and Altitude are now passed back from the sgp4 functions

js/jday.js

@@ -1,44 +1,62 @@
-// -----------------------------------------------------------------------------
-//
-//                           function jday.m
-//
-//  this function finds the julian date given the year, month, day, and time.
-//
-//  author        : david vallado                  719-573-2600   27 may 2002
-//
-//  revisions
-//                -
-//
-//  inputs          description                    range / units
-//    year        - year                           1900 .. 2100
-//    mon         - month                          1 .. 12
-//    day         - day                            1 .. 28,29,30,31
-//    hr          - universal time hour            0 .. 23
-//    min         - universal time min             0 .. 59
-//    sec         - universal time sec             0.0 .. 59.999
-//    whichtype   - julian .or. gregorian calender   'j' .or. 'g'
-//
-//  outputs       :
-//    jd          - julian date                    days from 4713 bc
-//
-//  locals        :
-//    none.
-//
-//  coupling      :
-//    none.
-//
-//  references    :
-//    vallado       2007, 189, alg 14, ex 3-14
-//
-// jd = jday(yr, mon, day, hr, min, sec)
-// -----------------------------------------------------------------------------
-
-function jday(yr, mon, day, hr, min, sec) {
-    return 367.0 * yr -
-        Math.floor((7 * (yr + Math.floor((mon + 9) / 12.0))) * 0.25) +
-        Math.floor(275 * mon / 9.0) +
-        day + 1721013.5 +
-        ((sec / 60.0 + min) / 60.0 + hr) / 24.0;
-        //  - 0.5 * sign(100.0 * yr + mon - 190002.5) + 0.5;
-}
-
+// -----------------------------------------------------------------------------
+//
+//                           function jday.m
+//
+//  this function finds the julian date given the year, month, day, and time.
+//
+//  author        : david vallado                  719-573-2600   27 may 2002
+//
+//  revisions
+//                -
+//
+//  inputs          description                    range / units
+//    year        - year                           1900 .. 2100
+//    mon         - month                          1 .. 12
+//    day         - day                            1 .. 28,29,30,31
+//    hr          - universal time hour            0 .. 23
+//    min         - universal time min             0 .. 59
+//    sec         - universal time sec             0.0 .. 59.999
+//    whichtype   - julian .or. gregorian calender   'j' .or. 'g'
+//
+//  outputs       :
+//    jd          - julian date                    days from 4713 bc
+//
+//  locals        :
+//    none.
+//
+//  coupling      :
+//    none.
+//
+//  references    :
+//    vallado       2007, 189, alg 14, ex 3-14
+//
+// jd = jday(yr, mon, day, hr, min, sec)
+// -----------------------------------------------------------------------------
+
+function jday(yr, mon, day, hr, min, sec) {
+    return 367.0 * yr -
+        Math.floor((7 * (yr + Math.floor((mon + 9) / 12.0))) * 0.25) +
+        Math.floor(275 * mon / 9.0) +
+        day + 1721013.5 +
+        ((sec / 60.0 + min) / 60.0 + hr) / 24.0;
+        //  - 0.5 * sign(100.0 * yr + mon - 190002.5) + 0.5;
+}
+
+/**
+* Added functions to support finding geodetic position
+*/
+function ThetaG_JD(jd) {
+    var UT = 0.0, TU = 0.0, GMST = 0.0;
+    var secday = 8.6400E4;
+    var omega_E = 1.00273790934;
+    var twopi = 2.0 * Math.PI;
+
+    UT = Frac(jd + 0.5);
+    jd = jd - UT;
+    TU = (jd - 2451545.0) / 36525;
+    GMST = 24110.54841 + TU * (8640184.812866 + TU * (0.093104 - TU * 6.2E-6));
+    GMST = Modulus(GMST + secday * omega_E * UT, secday);
+
+    return (twopi * GMST / secday);
+}
+

js/math_utils.js

@@ -37,4 +37,38 @@ function dot(a, b) {
 }
 
 
+/**
+* Added functions to support finding geodetic position
+*/
+function FMod2p(x) {
+    var i = 0;
+    var ret_val = 0.0;
+    var twopi = 2.0 * Math.PI;
+
+    ret_val = x;
+    i = parseInt(ret_val / twopi);
+    ret_val -= i * twopi;
 
+    if (ret_val < 0.0)
+        ret_val += twopi;
+
+    return ret_val;
+}
+
+function Sqr(arg) {
+    return (arg * arg);
+}
+
+function Frac(arg) {
+    return(arg - Math.floor(arg));
+}
+
+function Modulus(arg1, arg2) {
+    return arg1 - (parseInt(arg1 / arg2)) * arg2;
+}
+
+function Degrees(arg) {
+    var deg2rad =  1.745329251994330E-2;
+
+    return (arg / deg2rad);
+}

js/post.js

@@ -0,0 +1,33 @@
+var geodetic_t = function() {
+    lat = 0.0;
+    lon = 0.0;
+    alt = 0.0;
+    theta = 0.0;
+}
+
+function Calculate_LatLonAlt(time, pos, geodetic) {
+    var r = 0.0, e2 = 0.0, phi = 0.0, c = 0.0;
+    var f = 3.35281066474748E-3;
+    var xkmper = 6.378137E3;
+    var pio2 = 1.57079632679489656;
+    var twopi = 2.0 * Math.PI;
+
+    geodetic.theta = Math.atan2(pos[1], pos[0]);
+    geodetic.lon = FMod2p(geodetic.theta - ThetaG_JD(time));
+
+    r = Math.sqrt(Sqr(pos[0]) + Sqr(pos[1]));
+    e2 = f * (2 - f);
+    geodetic.lat = Math.atan2(pos[2], r);
+
+    do {
+        phi = geodetic.lat;
+        c = 1 / Math.sqrt(1 - e2 * Sqr(Math.sin(phi)));
+        geodetic.lat = Math.atan2(pos[2] + xkmper * c * e2 * Math.sin(phi), r);
+
+    } while (Math.abs(geodetic.lat - phi) >= 1E-10);
+
+    geodetic.alt = r / Math.cos(geodetic.lat) - xkmper * c;
+
+    if (geodetic.lat > pio2)
+        geodetic.lat -= twopi;
+}