Python shapely unary_union in JavaScript

I have seen turf.js has union() but this isn’t equal to the unary_union.

Or does anyone know what the unary_union actually does? Maybe I can try to recreate it, I have seen the source code in python but it looked very complicated.

The below code takes two line coords and merges them into one. The it converts to a LineString for shapely to read. But not sure whats the purpose of the unary_union (but it is the only way that gives me the correct result when comparing with actual data).

The idea was to get the area before/after the intersects, unary_union helped with finding the area before the intersect and the other area after the intersect.

This is the full code of the program which gets me the areas of the intersected lines:

import numpy as np
from shapely.geometry import LineString
from shapely.ops import unary_union, polygonize

avg_coords = [(0.0, 0.0), (4.872117, 2.29658), (5.268545, 2.4639225), (5.664686, 2.6485724), (6.059776, 2.8966842), (6.695151, 3.0986626), (7.728006, 3.4045217), (8.522297, 3.652668), (9.157002, 3.895031), (10.191483, 4.1028132), (10.827622, 4.258638), (11.38593, 4.2933016), (11.86478, 4.3048816), (12.344586, 4.258769), (12.984073, 4.2126703), (13.942729, 4.1781383), (14.58212, 4.137809), (15.542498, 3.99943), (16.502588, 3.878359), (17.182951, 3.7745714), (18.262657, 3.6621647), (19.102558, 3.567045), (20.061789, 3.497897), (21.139917, 3.4806826), (22.097425, 3.5153809), (23.65388, 3.5414772), (24.851482, 3.541581), (26.04966, 3.507069), (27.72702, 3.463945), (28.925198, 3.429433), (29.883854, 3.3949006), (31.08246, 3.3344274), (31.92107, 3.317192), (33.716183, 3.3952322), (35.63192, 3.4213595), (37.427895, 3.4474766), (39.343628, 3.473604), (41.49874, 3.508406), (43.773468, 3.5518723), (46.287716, 3.595359), (49.28115, 3.6302335), (52.633293, 3.6997545), (54.30922, 3.7431688), (55.8651, 3.8038807), (58.738773, 3.8387446), (60.893887, 3.8735466), (63.647655, 3.9170544), (66.760704, 3.960593), (68.79663, 3.9607692), (70.23332, 3.986855), (72.867905, 3.995737), (75.38245, 4.0219164), (77.778656, 3.9615464), (79.337975, 3.8145657), (80.41826, 3.6675436), (80.899734, 3.5204697), (81.62059, 3.38207), (82.34045, 3.3042476), (83.30039, 3.1918304), (84.38039, 3.062116), (84.50359, 2.854434), (83.906364, 2.7591898), (83.669716, 2.586092), (83.43435, 2.3351095), (83.19727, 2.1879735), (82.84229, 1.9283267), (82.48516, 1.7984879), (81.65014, 1.5993768), (80.454544, 1.4781193), (79.13962, 1.3308897), (77.944595, 1.1750168), (76.39001, 1.0364205), (74.59633, 0.87184185), (71.60447, 0.741775), (70.04903, 0.6551017), (58.3, 0.0)]
model_coords = [(0.0, 0.0), (0.6699889, 0.18807), (1.339894, 0.37499), (2.009583, 0.55966), (2.67915, 0.74106), (3.348189, 0.91826), (4.016881, 1.0904), (4.685107, 1.2567), (5.359344, 1.418), (6.026172, 1.5706), (6.685472, 1.714), (7.350604, 1.8508), (8.021434, 1.9803), (8.684451, 2.0996), (9.346408, 2.2099), (10.0066, 2.311), (10.66665, 2.4028), (11.32436, 2.4853), (11.98068, 2.5585), (12.6356, 2.6225), (13.29005, 2.6775), (13.93507, 2.7232), (14.58554, 2.7609), (15.23346, 2.7903), (15.87982, 2.8116), (16.52556, 2.8254), (17.16867, 2.832), (17.80914, 2.8317), (18.44891, 2.825), (19.08598, 2.8124), (19.72132, 2.7944), (20.35491, 2.7713), (20.98673, 2.7438), (21.61675, 2.7121), (22.24398, 2.677), (22.86939, 2.6387), (23.49297, 2.5978), (24.1147, 2.5548), (24.73458, 2.51), (25.3526, 2.464), (25.96874, 2.4171), (26.58301, 2.3697), (27.1954, 2.3223), (27.80491, 2.2751), (28.41354, 2.2285), (29.02028, 2.1829), (29.62512, 2.1384), (30.22809, 2.0954), (30.82917, 2.0541), (31.42837, 2.0147), (32.02669, 1.9775), (32.62215, 1.9425), (33.21674, 1.9099), (33.80945, 1.8799), (34.40032, 1.8525), (34.98933, 1.8277), (35.5765, 1.8058), (36.16283, 1.7865), (36.74733, 1.7701), (37.33002, 1.7564), (37.91187, 1.7455), (38.49092, 1.7372), (39.06917, 1.7316), (39.64661, 1.7285), (40.22127, 1.7279), (40.79514, 1.7297), (41.36723, 1.7337), (41.93759, 1.7399), (42.50707, 1.748), (43.07386, 1.7581), (43.63995, 1.7699), (44.20512, 1.7832), (44.76772, 1.7981), (45.3295, 1.8143), (45.88948, 1.8318), (46.44767, 1.8504), (47.00525, 1.8703), (47.55994, 1.8911), (48.11392, 1.9129), (48.6661, 1.9356), (49.21658, 1.959), (49.76518, 1.9832), (50.31305, 2.0079), (50.85824, 2.033), (51.40252, 2.0586), (51.94501, 2.0845), (52.48579, 2.1107), (53.02467, 2.1369), (53.56185, 2.1632), (54.09715, 2.1895), (54.63171, 2.2156), (55.1634, 2.2416), (55.69329, 2.2674), (56.22236, 2.2928), (56.74855, 2.3179), (57.27392, 2.3426), (57.7964, 2.3668), (58.31709, 2.3905), (58.83687, 2.4136), (59.35905, 2.4365), (59.87414, 2.4585), (60.38831, 2.4798), (60.8996, 2.5006), (61.40888, 2.5207), (61.91636, 2.5401), (62.42194, 2.5589), (62.92551, 2.577), (63.42729, 2.5945), (63.92607, 2.6113), (64.42384, 2.6275), (64.91873, 2.643), (65.4127, 2.658), (65.90369, 2.6724), (66.39266, 2.6862), (66.87964, 2.6995), (67.36373, 2.7123), (67.84679, 2.7246), (68.32689, 2.7364), (68.80595, 2.7478), (69.28194, 2.7588), (69.756, 2.7695), (70.22709, 2.7798), (70.69707, 2.7898), (71.16405, 2.7995), (71.62902, 2.809), (72.0919, 2.8183), (72.55277, 2.8273), (73.01067, 2.8362), (73.46734, 2.845), (73.92112, 2.8536), (74.37269, 2.8622), (74.82127, 2.8706), (75.26884, 2.8791), (75.71322, 2.8875), (76.15559, 2.8958), (76.59488, 2.9042), (77.03304, 2.9126), (77.46812, 2.921), (77.90111, 2.9294), (78.33199, 2.9379), (78.75986, 2.9464), (79.18652, 2.955), (79.60912, 2.9637), (80.03049, 2.9724), (80.44985, 2.9811), (80.86613, 2.99), (81.2802, 2.9989), (81.69118, 3.0078), (82.10006, 3.0168), (82.50674, 3.0259), (82.91132, 3.035), (83.31379, 3.0441), (83.71307, 3.0533), (84.10925, 3.0625), (84.50421, 3.0717), (84.8961, 3.0809), (85.28577, 3.0901), (85.67334, 3.0993), (86.05771, 3.1085), (86.43989, 3.1176), (86.81896, 3.1267), (87.19585, 3.1358), (87.57063, 3.1448), (87.94319, 3.1537), (88.31257, 3.1626), (88.67973, 3.1713), (89.04372, 3.18), (89.40659, 3.1886), (89.7652, 3.197), (90.12457, 3.2053), (90.47256, 3.2135), (90.82946, 3.2216), (91.17545, 3.2295), (91.52045, 3.2373), (91.86441, 3.2449), (92.20641, 3.2524), (92.54739, 3.2597), (92.88728, 3.2669), (93.21538, 3.2739), (93.55325, 3.2807), (93.87924, 3.2874), (94.20424, 3.2939), (94.52822, 3.3002), (94.85012, 3.3064), (95.16219, 3.3123), (95.48208, 3.3182), (95.79107, 3.3238), (96.09807, 3.3293), (96.40505, 3.3346), (96.71003, 3.3397), (97.01401, 3.3447), (97.31592, 3.3496), (97.60799, 3.3542), (97.90789, 3.3587), (98.19686, 3.3631), (98.48386, 3.3673), (98.77085, 3.3714), (99.05574, 3.3753), (99.32983, 3.3791), (99.6127, 3.3828), (99.8837, 3.3863), (100.1538, 3.3897), (100.4326, 3.393), (100.6897, 3.3961), (100.9566, 3.3991), (101.2215, 3.402), (101.4756, 3.4048), (101.7375, 3.4075), (101.9885, 3.4101), (102.2385, 3.4126), (102.4875, 3.4149), (102.7354, 3.4172), (102.9714, 3.4194), (103.2163, 3.4214), (103.4493, 3.4234), (103.6823, 3.4253), (103.9133, 3.4271), (104.1433, 3.4288), (104.3712, 3.4304), (104.5882, 3.4319), (104.8141, 3.4333), (105.0291, 3.4346), (105.2421, 3.4358), (105.4541, 3.437), (105.6651, 3.438), (105.8751, 3.439), (106.083, 3.4399), (106.28, 3.4407), (106.4759, 3.4414), (106.6699, 3.442), (106.8629, 3.4425), (107.0549, 3.443), (107.2458, 3.4433), (107.4249, 3.4435), (107.6128, 3.4437), (107.7897, 3.4438), (107.9647, 3.4437), (108.1387, 3.4436), (108.3116, 3.4433), (108.4737, 3.443), (108.6436, 3.4426), (108.8027, 3.4421), (108.9706, 3.4414), (109.1265, 3.4407), (109.2814, 3.4399), (109.4255, 3.439), (109.5784, 3.4379), (109.7195, 3.4368), (109.8694, 3.4356), (110.0084, 3.4342), (110.1454, 3.4328), (110.2813, 3.4313), (110.4162, 3.4296), (110.5403, 3.4279), (110.6722, 3.426), (110.7932, 3.424), (110.9132, 3.422), (111.0322, 3.4198), (111.1492, 3.4175), (111.2651, 3.4151), (111.3701, 3.4127), (111.483, 3.4101), (111.585, 3.4074), (111.686, 3.4046), (111.786, 3.4017), (111.884, 3.3987), (111.9809, 3.3956), (112.0669, 3.3924), (112.1608, 3.3891), (112.2448, 3.3857), (112.3268, 3.3822), (112.4078, 3.3786), (112.4867, 3.3749), (112.5548, 3.3711), (112.6317, 3.3672), (112.6978, 3.3632), (112.7726, 3.3591), (112.8356, 3.3549), (112.8975, 3.3506), (112.9476, 3.3462), (113.0076, 3.3417), (113.0655, 3.3372), (113.1125, 3.3325), (113.1584, 3.3278), (113.2024, 3.3229), (113.2464, 3.318), (113.2884, 3.313), (113.3283, 3.3079), (113.3584, 3.3027), (113.3963, 3.2974), (113.4233, 3.292), (113.4492, 3.2865), (113.4742, 3.281), (113.4972, 3.2753), (113.5201, 3.2696), (113.5312, 3.2638), (113.5501, 3.2579), (113.5591, 3.2519), (113.5661, 3.2459), (113.5721, 3.2397), (113.577, 3.2335), (113.5809, 3.2272), (113.573, 3.2208), (113.5749, 3.2143), (113.5649, 3.2077), (113.5539, 3.2011), (113.5409, 3.1944), (113.5278, 3.1876), (113.5128, 3.1807), (113.4967, 3.1737), (113.4697, 3.1667), (113.4418, 3.1596), (113.4227, 3.1524), (113.3917, 3.145), (113.3597, 3.1375), (113.3266, 3.1298), (113.2827, 3.1218), (113.2475, 3.1136), (113.2016, 3.1051), (113.1635, 3.0964), (113.1155, 3.0873), (113.0655, 3.0779), (113.0144, 3.0683), (112.9525, 3.0583), (112.8994, 3.048), (112.8345, 3.0373), (112.7793, 3.0264), (112.7123, 3.0152), (112.6453, 3.0037), (112.5763, 2.9919), (112.5063, 2.9798), (112.4352, 2.9674), (112.3533, 2.9548), (112.2801, 2.9419), (112.1952, 2.9287), (112.1102, 2.9153), (112.034, 2.9017), (111.9361, 2.8879), (111.8481, 2.8739), (111.7581, 2.8597), (111.667, 2.8453), (111.5661, 2.8307), (111.473, 2.816), (111.3689, 2.801), (111.2639, 2.786), (111.1579, 2.7708), (111.0509, 2.7555), (110.9428, 2.74), (110.8239, 2.7245), (110.7138, 2.7088), (110.5928, 2.6931), (110.4709, 2.6772), (110.3578, 2.6613), (110.2338, 2.6453), (110.1087, 2.6292), (109.9826, 2.613), (109.8457, 2.5968), (109.7176, 2.5805), (109.5787, 2.5642), (109.4496, 2.5478), (109.3086, 2.5314), (109.1666, 2.5149), (109.0236, 2.4984), (108.8806, 2.4819), (108.7355, 2.4653), (108.5905, 2.4488), (108.4434, 2.4322), (108.2865, 2.4155), (108.1384, 2.3989), (107.9794, 2.3822), (107.8195, 2.3655), (107.6684, 2.3488), (107.5063, 2.3321), (107.3374, 2.3156), (107.1744, 2.2989), (107.0104, 2.2822), (106.8442, 2.2654), (106.6683, 2.2487), (106.5012, 2.232), (106.3242, 2.2152), (106.1452, 2.1985), (105.9662, 2.1818), (105.7862, 2.165), (105.6052, 2.1483), (105.4232, 2.1316), (105.2402, 2.1149), (105.0572, 2.0981), (104.8721, 2.0814), (104.6772, 2.0647), (104.492, 2.048), (104.295, 2.0313), (104.098, 2.0147), (103.9, 1.998), (103.701, 1.9813), (103.502, 1.9647), (103.301, 1.948), (103.1, 1.9314), (102.899, 1.9148), (102.6959, 1.8982), (102.483, 1.8816), (102.2789, 1.865), (102.0649, 1.8484), (101.8588, 1.8318), (101.6428, 1.8153), (101.4268, 1.7988), (101.2098, 1.7822), (100.9918, 1.7657), (100.7728, 1.7492), (100.5538, 1.7328), (100.3338, 1.7163), (100.1128, 1.6999), (99.89169, 1.6834), (99.65978, 1.667), (99.43769, 1.6506), (99.20477, 1.6343), (98.98066, 1.6179), (98.74665, 1.6016), (98.51164, 1.5852), (98.27574, 1.5689), (98.04964, 1.5527), (97.81264, 1.5364), (97.57562, 1.5202), (97.33752, 1.5039), (97.08962, 1.4877), (96.8506, 1.4716), (96.61061, 1.4554), (96.37051, 1.4393), (96.12058, 1.4232), (95.87949, 1.4071), (95.62759, 1.391), (95.38547, 1.375), (95.13258, 1.359), (94.88946, 1.343), (94.63548, 1.3271), (94.38145, 1.3111), (94.12645, 1.2952), (93.87144, 1.2793), (93.61545, 1.2635), (93.35946, 1.2477), (93.10343, 1.2319), (92.84642, 1.2161), (92.58843, 1.2004), (92.33042, 1.1846), (92.07232, 1.169), (91.8034, 1.1533), (91.54331, 1.1377), (91.2744, 1.1221), (91.0133, 1.1065), (90.7434, 1.091), (90.48229, 1.0755), (90.21139, 1.0601), (89.9493, 1.0446), (89.67728, 1.0292), (89.40428, 1.0139), (89.13137, 0.99855), (88.86826, 0.98325), (88.59427, 0.96799), (88.32026, 0.95277), (88.04527, 0.93758), (87.77126, 0.92242), (87.4972, 0.90731), (87.21732, 0.89222), (86.94719, 0.87718), (86.66711, 0.86217), (86.3773, 0.8472), (86.10719, 0.83227), (85.82721, 0.81738), (85.5472, 0.80252), (85.26721, 0.7877), (84.9872, 0.77292), (84.7071, 0.75819), (84.41721, 0.74349), (84.1371, 0.72883), (83.84721, 0.71421), (83.5671, 0.69963), (83.27721, 0.68509), (82.99711, 0.6706), (82.70711, 0.65615), (82.41721, 0.64173), (82.1371, 0.62736), (81.8471, 0.61304), (81.55722, 0.59875), (81.27709, 0.58451), (80.98712, 0.57031), (80.697, 0.55616), (80.39711, 0.54205), (80.10722, 0.52798), (79.8271, 0.51396), (79.53701, 0.49999), (79.23711, 0.48605), (78.9471, 0.47217), (78.65701, 0.45833), (78.3571, 0.44453), (78.06712, 0.43078), (77.77701, 0.41708), (77.4771, 0.40343), (77.18701, 0.38982), (76.8871, 0.37626), (76.59711, 0.36274), (76.30701, 0.34928), (76.0071, 0.33586), (75.7169, 0.32249), (75.4071, 0.30917), (75.11701, 0.29589), (74.8171, 0.28267), (74.52701, 0.26949), (74.22711, 0.25636), (73.937, 0.24329), (73.63691, 0.23026), (73.3271, 0.21728), (73.03699, 0.20436), (72.73712, 0.19148), (72.4469, 0.17865), (72.13712, 0.16588), (71.84701, 0.15315), (71.547, 0.14048), (71.24701, 0.12786), (70.947, 0.11528), (70.64701, 0.10277), (70.3471, 0.090298), (70.05691, 0.077883), (69.74712, 0.06552), (69.457, 0.05321), (69.1569, 0.040952), (68.84709, 0.028747), (68.557, 0.016595), (68.25701, 0.0)]

polygon_points = [] #creates a empty list where we will append the points to create the polygon

for xyvalue in avg_coords:
    polygon_points.append([xyvalue[0],xyvalue[1]]) #append all xy points for curve 1

for xyvalue in model_coords[::-1]:
    polygon_points.append([xyvalue[0],xyvalue[1]]) #append all xy points for curve 2 in the reverse order (from last point to first point)

for xyvalue in avg_coords[0:1]:
    polygon_points.append([xyvalue[0],xyvalue[1]]) #append the first point in curve 1 again, to it "closes" the polygon

line_non_simple = LineString(polygon_points) #converts the intersecting array to linestring
mls = unary_union(line_non_simple) #not quite sure what this does but it works

avg_poly = [] 
model_poly = []

for xyvalue in avg_coords:
    avg_poly.append([xyvalue[0],xyvalue[1]]) 

for xyvalue in model_coords:
    model_poly.append([xyvalue[0],xyvalue[1]]) 


line_non_simple = LineString(polygon_points)
mls = unary_union(line_non_simple)

Area_cal =[]

for polygon in polygonize(mls):
    Area_cal.append(polygon.area)
    print(polygon.area)# print area of each section 
    Area_poly = (np.asarray(Area_cal).sum())
    
print(Area_poly)#print combined area

When plotted it looks like this, the code gives me the area of the top section and right section.