How to add spatial reference information in distance calculation? [closed]

Question

Software: ArcGIS Pro

I have a long polyline with multiple vertices. I want shape length of only a portion of this polyline. For that I have extracted the coordinates of all vertices of this long polyline and created a list. I have removed the coordinates from this list which are not required, so that I have a list of coordinates only of the portion whose shape length is required.

Now i need to calculate the shape length using this coordinates list. For that i have used the following code:

import numpy as np
def dist_from_point_list(point_list):
    line = np.array(point_list, float)
    return np.sqrt(np.sum((line[1:] - line[:-1])**2, -1)).sum()
print(dist_from_point_list(point_list))

When I measure the distance in ArcGIS Pro, the shape length is different from what I get using this function in my code. I have to somehow use the spatial reference information in my code to get the correct spatial length.

I tried as follows:

feature_info = [[(469741.90079999994, 233745.38800000027), (469741.4121000003, 233745.19480000064), (469741.1469999999, 233745.08999999985), (469742.0535000004, 233743.93400000036), (469742.95999999996, 233742.77800000086), (469743.1457000002, 233741.93960000016), (469744.3021, 233736.71729999967), (469744.6370000001, 233735.20500000007), (469744.9084000001, 233734.10789999925), (469744.95710000023, 233733.9110000003), (469745.82519999985, 233730.40210000053), (469745.9199999999, 233730.0189999994), (469747.1799999997, 233724.37299999967), (469746.95799999963, 233723.80000000075), (469747.4139999999, 233722.3440000005), (469747.56900000013, 233721.86690000072), (469747.6469999999, 233721.73399999924), (469750.0284000002, 233713.38040000014), (469750.4979999997, 233711.73299999908), (469751.28199999966, 233710.97399999946), (469751.4919999996, 233710.39699999988), (469825.6730000004, 233504.0979999993), (469825.26400000043, 233504.92899999954), (469813.48900000006, 233531.3560000006), (469813.3729999997, 233531.6129999999), (469801.8559999997, 233561.35799999908), (469800.2570000002, 233563.26400000043), (469797.0800000001, 233570.77600000054), (469793.90299999993, 233578.28800000064), (469792.6009999998, 233580.41200000048), (469797.7457999997, 233582.2851999998), (469799.33100000024, 233582.86240000091), (469801.6150000002, 233583.69400000013), (469794.9391999999, 233599.6598000005), (469792.40390000027, 233605.72309999913), (469789.87600000016, 233611.7689999994), (469789.3559999997, 233613.37900000066), (469786.5020000003, 233620.32799999975), (469783.6370000001, 233627.3230000008), (469780.784, 233634.3440000005), (469777.8969999999, 233641.32200000063), (469775.2419999996, 233648.27800000086), (469772.51400000043, 233655.12189999968), (469769.9369999999, 233661.77999999933), (469765.5580000002, 233672.3900000006), (469764.8053000001, 233674.33830000088), (469761.61199999973, 233682.60400000028), (469757.9497999996, 233691.7310000006), (469757.62590000033, 233692.5382000003), (469756.5080000004, 233695.3239999991), (469754.17619999964, 233702.33110000007), (469753.43620000035, 233704.55440000072), (469752.5036000004, 233707.35669999942), (469751.57100000046, 233710.15909999982), (469751.4919999996, 233710.39699999988), (469750.87399999984, 233710.21829999983), (469914.5789999999, 233428.50999999978), (469914.88609999977, 233428.49760000035), (469916.05510000046, 233428.45069999993), (469918.4615000002, 233426.21199999936), (469921.8501000004, 233423.05959999934), (469930.1710000001, 233473.81299999915), (469929.324, 233474.09200000018), (469928.5959999999, 233470.64100000076), (469927.5410000002, 233466.39790000021), (469923.9411000004, 233456.26070000045), (469922.7379999999, 233452.87299999967), (469920.59530000016, 233446.5427000001), (469920.07799999975, 233445.01449999958), (469918.75739999954, 233441.11319999956), (469918.43099999987, 233440.1490000002), (469916.59669999965, 233433.80859999917), (469916.2450000001, 233432.59300000034), (469914.65809999965, 233428.70390000008), (469914.5789999999, 233428.50999999978), (469914.44600000046, 233428.54900000058), (469914.0614, 233428.11099999957), (469908.3674999997, 233421.62629999965), (469905.82799999975, 233418.73399999924), (469906.2189999996, 233418.75), (469906.31900000013, 233418.66200000048), (469912.2860000003, 233413.43989999965), (469912.1730000004, 233413.30599999987), (469911.7759999996, 233413.22199999914), (469904.25320000015, 233419.67679999955), (469901.9397, 233421.66169999912), (469899.4305999996, 233423.81460000016), (469889.17399999965, 233432.61500000022), (469880.9966000002, 233439.99540000036), (469875.89800000004, 233444.59699999914), (469861.96800000034, 233458.4539999999), (469852.60720000044, 233468.59249999933), (469845.44099999964, 233476.35400000028), (469838.574, 233483.48179999925), (469835.5120000001, 233486.66000000015), (469834.8194000004, 233488.11759999953), (469832.3590000002, 233493.29499999993), (469830.5712000001, 233496.18359999917), (469825.6730000004, 233504.0979999993), (469824.4938000003, 233500.06020000018)]]
features = []

for feature in feature_info:
    # Create a Polyline object based on the array of points
    # Append to the list of Polyline objects
    features.append(arcpy.Polyline(arcpy.Array([arcpy.Point(*coords) for coords in feature])))

# Persist a copy of the Polyline objects using CopyFeatures
tmp = arcpy.CopyFeatures_management(features, "memory/lineSegment")
length = [f[0] for f in arcpy.da.SearchCursor(tmp, 'SHAPE@LENGTH', spatial_reference=arcpy.SpatialReference(27700))][0]

print(length)

The length found is : 1074.598630135699

whereas the shape length from arcgis pro is : 471.116806

I don't see an option to upload the shape file used in my test :(

Why is this difference in length??

Answer 1

Using arcpy, you should probably create a Polyline object from the coordinates you have extracted, set the correct spatial reference, and then use its length property (cartesian length) or getLength().