Incorrect grid zone letter for UPS at the south pole

[Skhmt]

At the south pole, any longitude > -90 and < 90 (i.e. towards the prime meridian) gives the zone letter B, while longitudes > 90 but < -90 (i.e. towards the anti-meridian) gives the zone letter A. In other words, the zone letter at the south pole is being determined by the northing. This is incorrect.

DMA TM 8358,1 B-3.2:

If the easting is less than 2,000,000 meters the Grid Zone Designation will be Y or A depending on whether the point is in the North or South Polar region. If the easting is greater than 2,000,000 meters the Grid Zone Designation will be Z or B.

See also the wikipedia example.

I had an open PR but since the repo hasn't been touched in years, I just closed it. This is more to let anyone else know to not trust the grid zone letter for UPS at the south pole.

[ryanc16]

Just confirming this is still an issue.
I actually ran into this while writing unit tests in my own application and cross verifying using a different online coordinate conversion tool.

Issue is in two places in the code:

usng.js/src/usng.ts

Line 355 in 6442082

: (utmups.northing < 2000000 ? 'A' : 'B')

usng.js/src/usng.ts

Line 572 in 6442082

: (upsObject.northing < 2000000 ? 'A' : 'B')

Results below for longitudes -179 through 179 in the southern pole using the LLtoUTMUPS(lat, lon) method.

Click to expand

Lat: -80.1 Lon: -179 to 179

[-80.1,-179] -> A 1980772mE 898404mN
[-80.1,-178] -> A 1961549mE 898907mN
[-80.1,-177] -> A 1942338mE 899746mN
[-80.1,-176] -> A 1923145mE 900920mN
[-80.1,-175] -> A 1903975mE 902428mN
[-80.1,-174] -> A 1884834mE 904271mN
[-80.1,-173] -> A 1865729mE 906448mN
[-80.1,-172] -> A 1846664mE 908958mN
[-80.1,-171] -> A 1827646mE 911800mN
[-80.1,-170] -> A 1808681mE 914974mN
[-80.1,-169] -> A 1789773mE 918478mN
[-80.1,-168] -> A 1770930mE 922312mN
[-80.1,-167] -> A 1752157mE 926474mN
[-80.1,-166] -> A 1733459mE 930963mN
[-80.1,-165] -> A 1714842mE 935777mN
[-80.1,-164] -> A 1696313mE 940916mN
[-80.1,-163] -> A 1677875mE 946378mN
[-80.1,-162] -> A 1659536mE 952160mN
[-80.1,-161] -> A 1641301mE 958261mN
[-80.1,-160] -> A 1623174mE 964680mN
[-80.1,-159] -> A 1605163mE 971414mN
[-80.1,-158] -> A 1587272mE 978462mN
[-80.1,-157] -> A 1569506mE 985821mN
[-80.1,-156] -> A 1551872mE 993488mN
[-80.1,-155] -> A 1534374mE 1001463mN
[-80.1,-154] -> A 1517018mE 1009741mN
[-80.1,-153] -> A 1499810mE 1018321mN
[-80.1,-152] -> A 1482753mE 1027200mN
[-80.1,-151] -> A 1465854mE 1036375mN
[-80.1,-150] -> A 1449118mE 1045844mN
[-80.1,-149] -> A 1432549mE 1055604mN
[-80.1,-148] -> A 1416154mE 1065651mN
[-80.1,-147] -> A 1399936mE 1075983mN
[-80.1,-146] -> A 1383901mE 1086596mN
[-80.1,-145] -> A 1368054mE 1097488mN
[-80.1,-144] -> A 1352399mE 1108654mN
[-80.1,-143] -> A 1336942mE 1120092mN
[-80.1,-142] -> A 1321686mE 1131798mN
[-80.1,-141] -> A 1306637mE 1143768mN
[-80.1,-140] -> A 1291800mE 1156000mN
[-80.1,-139] -> A 1277178mE 1168488mN
[-80.1,-138] -> A 1262776mE 1181230mN
[-80.1,-137] -> A 1248599mE 1194221mN
[-80.1,-136] -> A 1234650mE 1207457mN
[-80.1,-135] -> A 1220935mE 1220935mN
[-80.1,-134] -> A 1207457mE 1234650mN
[-80.1,-133] -> A 1194221mE 1248599mN
[-80.1,-132] -> A 1181230mE 1262776mN
[-80.1,-131] -> A 1168488mE 1277178mN
[-80.1,-130] -> A 1156000mE 1291800mN
[-80.1,-129] -> A 1143768mE 1306637mN
[-80.1,-128] -> A 1131798mE 1321686mN
[-80.1,-127] -> A 1120092mE 1336942mN
[-80.1,-126] -> A 1108654mE 1352399mN
[-80.1,-125] -> A 1097488mE 1368054mN
[-80.1,-124] -> A 1086596mE 1383901mN
[-80.1,-123] -> A 1075983mE 1399936mN
[-80.1,-122] -> A 1065651mE 1416154mN
[-80.1,-121] -> A 1055604mE 1432549mN
[-80.1,-120] -> A 1045844mE 1449118mN
[-80.1,-119] -> A 1036375mE 1465854mN
[-80.1,-118] -> A 1027200mE 1482753mN
[-80.1,-117] -> A 1018321mE 1499810mN
[-80.1,-116] -> A 1009741mE 1517018mN
[-80.1,-115] -> A 1001463mE 1534374mN
[-80.1,-114] -> A 993488mE 1551872mN
[-80.1,-113] -> A 985821mE 1569506mN
[-80.1,-112] -> A 978462mE 1587272mN
[-80.1,-111] -> A 971414mE 1605163mN
[-80.1,-110] -> A 964680mE 1623174mN
[-80.1,-109] -> A 958261mE 1641301mN
[-80.1,-108] -> A 952160mE 1659536mN
[-80.1,-107] -> A 946378mE 1677875mN
[-80.1,-106] -> A 940916mE 1696313mN
[-80.1,-105] -> A 935777mE 1714842mN
[-80.1,-104] -> A 930963mE 1733459mN
[-80.1,-103] -> A 926474mE 1752157mN
[-80.1,-102] -> A 922312mE 1770930mN
[-80.1,-101] -> A 918478mE 1789773mN
[-80.1,-100] -> A 914974mE 1808681mN
[-80.1, -99] -> A 911800mE 1827646mN
[-80.1, -98] -> A 908958mE 1846664mN
[-80.1, -97] -> A 906448mE 1865729mN
[-80.1, -96] -> A 904271mE 1884834mN
[-80.1, -95] -> A 902428mE 1903975mN
[-80.1, -94] -> A 900920mE 1923145mN
[-80.1, -93] -> A 899746mE 1942338mN
[-80.1, -92] -> A 898907mE 1961549mN
[-80.1, -91] -> A 898404mE 1980772mN
[-80.1, -90] -> B 898236mE 2000000mN
[-80.1, -89] -> B 898404mE 2019228mN
[-80.1, -88] -> B 898907mE 2038451mN
[-80.1, -87] -> B 899746mE 2057662mN
[-80.1, -86] -> B 900920mE 2076855mN
[-80.1, -85] -> B 902428mE 2096025mN
[-80.1, -84] -> B 904271mE 2115166mN
[-80.1, -83] -> B 906448mE 2134271mN
[-80.1, -82] -> B 908958mE 2153336mN
[-80.1, -81] -> B 911800mE 2172354mN
[-80.1, -80] -> B 914974mE 2191319mN
[-80.1, -79] -> B 918478mE 2210227mN
[-80.1, -78] -> B 922312mE 2229070mN
[-80.1, -77] -> B 926474mE 2247843mN
[-80.1, -76] -> B 930963mE 2266541mN
[-80.1, -75] -> B 935777mE 2285158mN
[-80.1, -74] -> B 940916mE 2303687mN
[-80.1, -73] -> B 946378mE 2322125mN
[-80.1, -72] -> B 952160mE 2340464mN
[-80.1, -71] -> B 958261mE 2358699mN
[-80.1, -70] -> B 964680mE 2376826mN
[-80.1, -69] -> B 971414mE 2394837mN
[-80.1, -68] -> B 978462mE 2412728mN
[-80.1, -67] -> B 985821mE 2430494mN
[-80.1, -66] -> B 993488mE 2448128mN
[-80.1, -65] -> B 1001463mE 2465626mN
[-80.1, -64] -> B 1009741mE 2482982mN
[-80.1, -63] -> B 1018321mE 2500190mN
[-80.1, -62] -> B 1027200mE 2517247mN
[-80.1, -61] -> B 1036375mE 2534146mN
[-80.1, -60] -> B 1045844mE 2550882mN
[-80.1, -59] -> B 1055604mE 2567451mN
[-80.1, -58] -> B 1065651mE 2583846mN
[-80.1, -57] -> B 1075983mE 2600064mN
[-80.1, -56] -> B 1086596mE 2616099mN
[-80.1, -55] -> B 1097488mE 2631946mN
[-80.1, -54] -> B 1108654mE 2647601mN
[-80.1, -53] -> B 1120092mE 2663058mN
[-80.1, -52] -> B 1131798mE 2678314mN
[-80.1, -51] -> B 1143768mE 2693363mN
[-80.1, -50] -> B 1156000mE 2708200mN
[-80.1, -49] -> B 1168488mE 2722822mN
[-80.1, -48] -> B 1181230mE 2737224mN
[-80.1, -47] -> B 1194221mE 2751401mN
[-80.1, -46] -> B 1207457mE 2765350mN
[-80.1, -45] -> B 1220935mE 2779065mN
[-80.1, -44] -> B 1234650mE 2792543mN
[-80.1, -43] -> B 1248599mE 2805779mN
[-80.1, -42] -> B 1262776mE 2818770mN
[-80.1, -41] -> B 1277178mE 2831512mN
[-80.1, -40] -> B 1291800mE 2844000mN
[-80.1, -39] -> B 1306637mE 2856232mN
[-80.1, -38] -> B 1321686mE 2868202mN
[-80.1, -37] -> B 1336942mE 2879908mN
[-80.1, -36] -> B 1352399mE 2891346mN
[-80.1, -35] -> B 1368054mE 2902512mN
[-80.1, -34] -> B 1383901mE 2913404mN
[-80.1, -33] -> B 1399936mE 2924017mN
[-80.1, -32] -> B 1416154mE 2934349mN
[-80.1, -31] -> B 1432549mE 2944396mN
[-80.1, -30] -> B 1449118mE 2954156mN
[-80.1, -29] -> B 1465854mE 2963625mN
[-80.1, -28] -> B 1482753mE 2972800mN
[-80.1, -27] -> B 1499810mE 2981679mN
[-80.1, -26] -> B 1517018mE 2990259mN
[-80.1, -25] -> B 1534374mE 2998537mN
[-80.1, -24] -> B 1551872mE 3006512mN
[-80.1, -23] -> B 1569506mE 3014179mN
[-80.1, -22] -> B 1587272mE 3021538mN
[-80.1, -21] -> B 1605163mE 3028586mN
[-80.1, -20] -> B 1623174mE 3035320mN
[-80.1, -19] -> B 1641301mE 3041739mN
[-80.1, -18] -> B 1659536mE 3047840mN
[-80.1, -17] -> B 1677875mE 3053622mN
[-80.1, -16] -> B 1696313mE 3059084mN
[-80.1, -15] -> B 1714842mE 3064223mN
[-80.1, -14] -> B 1733459mE 3069037mN
[-80.1, -13] -> B 1752157mE 3073526mN
[-80.1, -12] -> B 1770930mE 3077688mN
[-80.1, -11] -> B 1789773mE 3081522mN
[-80.1, -10] -> B 1808681mE 3085026mN
[-80.1,  -9] -> B 1827646mE 3088200mN
[-80.1,  -8] -> B 1846664mE 3091042mN
[-80.1,  -7] -> B 1865729mE 3093552mN
[-80.1,  -6] -> B 1884834mE 3095729mN
[-80.1,  -5] -> B 1903975mE 3097572mN
[-80.1,  -4] -> B 1923145mE 3099080mN
[-80.1,  -3] -> B 1942338mE 3100254mN
[-80.1,  -2] -> B 1961549mE 3101093mN
[-80.1,  -1] -> B 1980772mE 3101596mN
[-80.1,   0] -> B 2000000mE 3101764mN
[-80.1,   1] -> B 2019228mE 3101596mN
[-80.1,   2] -> B 2038451mE 3101093mN
[-80.1,   3] -> B 2057662mE 3100254mN
[-80.1,   4] -> B 2076855mE 3099080mN
[-80.1,   5] -> B 2096025mE 3097572mN
[-80.1,   6] -> B 2115166mE 3095729mN
[-80.1,   7] -> B 2134271mE 3093552mN
[-80.1,   8] -> B 2153336mE 3091042mN
[-80.1,   9] -> B 2172354mE 3088200mN
[-80.1,  10] -> B 2191319mE 3085026mN
[-80.1,  11] -> B 2210227mE 3081522mN
[-80.1,  12] -> B 2229070mE 3077688mN
[-80.1,  13] -> B 2247843mE 3073526mN
[-80.1,  14] -> B 2266541mE 3069037mN
[-80.1,  15] -> B 2285158mE 3064223mN
[-80.1,  16] -> B 2303687mE 3059084mN
[-80.1,  17] -> B 2322125mE 3053622mN
[-80.1,  18] -> B 2340464mE 3047840mN
[-80.1,  19] -> B 2358699mE 3041739mN
[-80.1,  20] -> B 2376826mE 3035320mN
[-80.1,  21] -> B 2394837mE 3028586mN
[-80.1,  22] -> B 2412728mE 3021538mN
[-80.1,  23] -> B 2430494mE 3014179mN
[-80.1,  24] -> B 2448128mE 3006512mN
[-80.1,  25] -> B 2465626mE 2998537mN
[-80.1,  26] -> B 2482982mE 2990259mN
[-80.1,  27] -> B 2500190mE 2981679mN
[-80.1,  28] -> B 2517247mE 2972800mN
[-80.1,  29] -> B 2534146mE 2963625mN
[-80.1,  30] -> B 2550882mE 2954156mN
[-80.1,  31] -> B 2567451mE 2944396mN
[-80.1,  32] -> B 2583846mE 2934349mN
[-80.1,  33] -> B 2600064mE 2924017mN
[-80.1,  34] -> B 2616099mE 2913404mN
[-80.1,  35] -> B 2631946mE 2902512mN
[-80.1,  36] -> B 2647601mE 2891346mN
[-80.1,  37] -> B 2663058mE 2879908mN
[-80.1,  38] -> B 2678314mE 2868202mN
[-80.1,  39] -> B 2693363mE 2856232mN
[-80.1,  40] -> B 2708200mE 2844000mN
[-80.1,  41] -> B 2722822mE 2831512mN
[-80.1,  42] -> B 2737224mE 2818770mN
[-80.1,  43] -> B 2751401mE 2805779mN
[-80.1,  44] -> B 2765350mE 2792543mN
[-80.1,  45] -> B 2779065mE 2779065mN
[-80.1,  46] -> B 2792543mE 2765350mN
[-80.1,  47] -> B 2805779mE 2751401mN
[-80.1,  48] -> B 2818770mE 2737224mN
[-80.1,  49] -> B 2831512mE 2722822mN
[-80.1,  50] -> B 2844000mE 2708200mN
[-80.1,  51] -> B 2856232mE 2693363mN
[-80.1,  52] -> B 2868202mE 2678314mN
[-80.1,  53] -> B 2879908mE 2663058mN
[-80.1,  54] -> B 2891346mE 2647601mN
[-80.1,  55] -> B 2902512mE 2631946mN
[-80.1,  56] -> B 2913404mE 2616099mN
[-80.1,  57] -> B 2924017mE 2600064mN
[-80.1,  58] -> B 2934349mE 2583846mN
[-80.1,  59] -> B 2944396mE 2567451mN
[-80.1,  60] -> B 2954156mE 2550882mN
[-80.1,  61] -> B 2963625mE 2534146mN
[-80.1,  62] -> B 2972800mE 2517247mN
[-80.1,  63] -> B 2981679mE 2500190mN
[-80.1,  64] -> B 2990259mE 2482982mN
[-80.1,  65] -> B 2998537mE 2465626mN
[-80.1,  66] -> B 3006512mE 2448128mN
[-80.1,  67] -> B 3014179mE 2430494mN
[-80.1,  68] -> B 3021538mE 2412728mN
[-80.1,  69] -> B 3028586mE 2394837mN
[-80.1,  70] -> B 3035320mE 2376826mN
[-80.1,  71] -> B 3041739mE 2358699mN
[-80.1,  72] -> B 3047840mE 2340464mN
[-80.1,  73] -> B 3053622mE 2322125mN
[-80.1,  74] -> B 3059084mE 2303687mN
[-80.1,  75] -> B 3064223mE 2285158mN
[-80.1,  76] -> B 3069037mE 2266541mN
[-80.1,  77] -> B 3073526mE 2247843mN
[-80.1,  78] -> B 3077688mE 2229070mN
[-80.1,  79] -> B 3081522mE 2210227mN
[-80.1,  80] -> B 3085026mE 2191319mN
[-80.1,  81] -> B 3088200mE 2172354mN
[-80.1,  82] -> B 3091042mE 2153336mN
[-80.1,  83] -> B 3093552mE 2134271mN
[-80.1,  84] -> B 3095729mE 2115166mN
[-80.1,  85] -> B 3097572mE 2096025mN
[-80.1,  86] -> B 3099080mE 2076855mN
[-80.1,  87] -> B 3100254mE 2057662mN
[-80.1,  88] -> B 3101093mE 2038451mN
[-80.1,  89] -> B 3101596mE 2019228mN
[-80.1,  90] -> B 3101764mE 2000000mN
[-80.1,  91] -> A 3101596mE 1980772mN
[-80.1,  92] -> A 3101093mE 1961549mN
[-80.1,  93] -> A 3100254mE 1942338mN
[-80.1,  94] -> A 3099080mE 1923145mN
[-80.1,  95] -> A 3097572mE 1903975mN
[-80.1,  96] -> A 3095729mE 1884834mN
[-80.1,  97] -> A 3093552mE 1865729mN
[-80.1,  98] -> A 3091042mE 1846664mN
[-80.1,  99] -> A 3088200mE 1827646mN
[-80.1, 100] -> A 3085026mE 1808681mN
[-80.1, 101] -> A 3081522mE 1789773mN
[-80.1, 102] -> A 3077688mE 1770930mN
[-80.1, 103] -> A 3073526mE 1752157mN
[-80.1, 104] -> A 3069037mE 1733459mN
[-80.1, 105] -> A 3064223mE 1714842mN
[-80.1, 106] -> A 3059084mE 1696313mN
[-80.1, 107] -> A 3053622mE 1677875mN
[-80.1, 108] -> A 3047840mE 1659536mN
[-80.1, 109] -> A 3041739mE 1641301mN
[-80.1, 110] -> A 3035320mE 1623174mN
[-80.1, 111] -> A 3028586mE 1605163mN
[-80.1, 112] -> A 3021538mE 1587272mN
[-80.1, 113] -> A 3014179mE 1569506mN
[-80.1, 114] -> A 3006512mE 1551872mN
[-80.1, 115] -> A 2998537mE 1534374mN
[-80.1, 116] -> A 2990259mE 1517018mN
[-80.1, 117] -> A 2981679mE 1499810mN
[-80.1, 118] -> A 2972800mE 1482753mN
[-80.1, 119] -> A 2963625mE 1465854mN
[-80.1, 120] -> A 2954156mE 1449118mN
[-80.1, 121] -> A 2944396mE 1432549mN
[-80.1, 122] -> A 2934349mE 1416154mN
[-80.1, 123] -> A 2924017mE 1399936mN
[-80.1, 124] -> A 2913404mE 1383901mN
[-80.1, 125] -> A 2902512mE 1368054mN
[-80.1, 126] -> A 2891346mE 1352399mN
[-80.1, 127] -> A 2879908mE 1336942mN
[-80.1, 128] -> A 2868202mE 1321686mN
[-80.1, 129] -> A 2856232mE 1306637mN
[-80.1, 130] -> A 2844000mE 1291800mN
[-80.1, 131] -> A 2831512mE 1277178mN
[-80.1, 132] -> A 2818770mE 1262776mN
[-80.1, 133] -> A 2805779mE 1248599mN
[-80.1, 134] -> A 2792543mE 1234650mN
[-80.1, 135] -> A 2779065mE 1220935mN
[-80.1, 136] -> A 2765350mE 1207457mN
[-80.1, 137] -> A 2751401mE 1194221mN
[-80.1, 138] -> A 2737224mE 1181230mN
[-80.1, 139] -> A 2722822mE 1168488mN
[-80.1, 140] -> A 2708200mE 1156000mN
[-80.1, 141] -> A 2693363mE 1143768mN
[-80.1, 142] -> A 2678314mE 1131798mN
[-80.1, 143] -> A 2663058mE 1120092mN
[-80.1, 144] -> A 2647601mE 1108654mN
[-80.1, 145] -> A 2631946mE 1097488mN
[-80.1, 146] -> A 2616099mE 1086596mN
[-80.1, 147] -> A 2600064mE 1075983mN
[-80.1, 148] -> A 2583846mE 1065651mN
[-80.1, 149] -> A 2567451mE 1055604mN
[-80.1, 150] -> A 2550882mE 1045844mN
[-80.1, 151] -> A 2534146mE 1036375mN
[-80.1, 152] -> A 2517247mE 1027200mN
[-80.1, 153] -> A 2500190mE 1018321mN
[-80.1, 154] -> A 2482982mE 1009741mN
[-80.1, 155] -> A 2465626mE 1001463mN
[-80.1, 156] -> A 2448128mE 993488mN
[-80.1, 157] -> A 2430494mE 985821mN
[-80.1, 158] -> A 2412728mE 978462mN
[-80.1, 159] -> A 2394837mE 971414mN
[-80.1, 160] -> A 2376826mE 964680mN
[-80.1, 161] -> A 2358699mE 958261mN
[-80.1, 162] -> A 2340464mE 952160mN
[-80.1, 163] -> A 2322125mE 946378mN
[-80.1, 164] -> A 2303687mE 940916mN
[-80.1, 165] -> A 2285158mE 935777mN
[-80.1, 166] -> A 2266541mE 930963mN
[-80.1, 167] -> A 2247843mE 926474mN
[-80.1, 168] -> A 2229070mE 922312mN
[-80.1, 169] -> A 2210227mE 918478mN
[-80.1, 170] -> A 2191319mE 914974mN
[-80.1, 171] -> A 2172354mE 911800mN
[-80.1, 172] -> A 2153336mE 908958mN
[-80.1, 173] -> A 2134271mE 906448mN
[-80.1, 174] -> A 2115166mE 904271mN
[-80.1, 175] -> A 2096025mE 902428mN
[-80.1, 176] -> A 2076855mE 900920mN
[-80.1, 177] -> A 2057662mE 899746mN
[-80.1, 178] -> A 2038451mE 898907mN
[-80.1, 179] -> A 2019228mE 898404mN

[kleinjakob]

I wanted to report the same problem, @Skhmt maybe you can share your fixed fork?

[Skhmt]

it was exactly what @ryanc16 did, just fixed those two lines. https://github.com/codice/usng.js/pull/50/files

[ryanc16]

Ideally a pull request should be made that both fixes this and adds unit tests proving it's correct. Some good unit tests would have caught this when the conversion methods were added.