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Error transferring math code between javascript and java

I have a problem with porting javascript code that converts values ​​between Latitude / Longitude and OS National Grid Reference points in Java. ( http://www.movable-type.co.uk/scripts/latlong-gridref.html )

I get different results in some mathematical operations. I have included javascript and java code below, but what happens is the results of calculating Ma in 0.04195508514183418 in javascript and 0.04195511450680837 in java. I printed the input for the calculation, and they are the same.

This is the javascript code:

 OsGridRef.osGridToLatLong = function(gridref) { var E = gridref.easting; var N = gridref.northing; var a = 6377563.396, b = 6356256.910; // Airy 1830 major & minor semi-axes var F0 = 0.9996012717; // NatGrid scale factor on central meridian var lat0 = 49*Math.PI/180, lon0 = -2*Math.PI/180; // NatGrid true origin var N0 = -100000, E0 = 400000; // northing & easting of true origin, metres var e2 = 1 - (b*b)/(a*a); // eccentricity squared var n = (ab)/(a+b), n2 = n*n, n3 = n*n*n; var lat=lat0, M=0; var count = 0; do { count++; lat = (N-N0-M)/(a*F0) + lat; console.log("pre ma calc"); console.log("n = " + n); console.log("n2 = " + n2); console.log("n3 = " + n3); console.log("lat = " + lat); console.log("lat0 = " + lat0); var Ma = (1 + n + (5/4)*n2 + (5/4)*n3) * (lat-lat0); console.log("post ma calc ma = " + Ma);

This is the conclusion:

 pre ma calc test.html:68 n = 0.0016732202503250534 test.html:69 n2 = 0.0000027996660060978346 test.html:70 n3 = 4.684457855549562e-9 test.html:71 lat = 0.8970962185213205 test.html:72 lat0 = 0.8552113334772214 test.html:73 post ma calc ma = 0.04195511450680837

And here is the Java code:

 LatLon osGridToLatLong(OsGridRef osGridRef) { int E = osGridRef.easting; int N = osGridRef.northing; double a = 6377563.396, b = 6356256.910; // Airy 1830 major & minor semi-axes double F0 = 0.9996012717; // NatGrid scale factor on central meridian double lat0 = 49*Math.PI/180, lon0 = -2*Math.PI/180; // NatGrid true origin double N0 = -100000, E0 = 400000; // northing & easting of true origin, metres double e2 = 1 - (b*b)/(a*a); // eccentricity squared double n = (ab)/(a+b), n2 = n*n, n3 = n*n*n; double lat=lat0, M=0; int count = 0; do { count++; lat = (N-N0-M)/(a*F0) + lat; Log.e(TAG, "pre ma calc"); Log.e(TAG, "n = " + n); Log.e(TAG, "n2 = " + n2); Log.e(TAG, "n3 = " + n3); Log.e(TAG, "lat = " + lat); Log.e(TAG, "lat0 = " + lat0); double Ma = (1 + n + (5/4)*n2 + (5/4)*n3) * (lat-lat0); Log.e(TAG, "post ma calc ma = " + String.valueOf(Ma)); double Mb = (3*n + 3*n*n + (21/8)*n3) * Math.sin(lat-lat0) * Math.cos(lat+lat0); double Mc = ((15/8)*n2 + (15/8)*n3) * Math.sin(2*(lat-lat0)) * Math.cos(2*(lat+lat0)); double Md = (35/24)*n3 * Math.sin(3*(lat-lat0)) * Math.cos(3*(lat+lat0)); M = b * F0 * (Ma - Mb + Mc - Md); // meridional arc } while (N-N0-M >= 0.00001); // ie until < 0.01mm

This is the conclusion:

 07-03 12:36:03.413: E/DSDS(779): pre ma calc 07-03 12:36:03.423: E/DSDS(779): n = 0.0016732202503250534 07-03 12:36:03.423: E/DSDS(779): n2 = 2.7996660060978346E-6 07-03 12:36:03.443: E/DSDS(779): n3 = 4.684457855549562E-9 07-03 12:36:03.473: E/DSDS(779): lat = 0.8970962185213205 07-03 12:36:03.473: E/DSDS(779): lat0 = 0.8552113334772214 07-03 12:36:03.473: E/DSDS(779): post ma calc ma = 0.04195508514183418
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1 answer

5/4 will be interpreted as integer division and therefore will give 5/4 5 / 4 = 1.25 = 1

Change it to 5.0 / 4 so that it uses floating point types instead of integers. This occurs when calculating Ma, Mb, Mg, and Md several times.

Perhaps this already makes your results even, but it certainly makes them correct, since mathematics should work on its own. I think you also adjusted the code.

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Source: https://habr.com/ru/post/1489503/

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