如何用geopy计算两点间直线上任意位置的经纬度？

我正在使用geopy模拟物体在两个地理点间移动时的位置映射，需要计算该物体在理论行程中任意阶段的经纬度：例如从巴黎到纽约，0%对应巴黎，100%对应纽约，50%对应行程过半时的中点（仅考虑两点间直线，不考虑实际航线或真实物体轨迹）。

我的代码如下：

from geopy.distance import geodesic as GD

start = (48.8567, 2.3508) # Paris
end = (40.7128, 74.0060) # New York

distance_between = GD(start, end).km

print(f"{distance_between} km between Paris and New York")

pct_travelled = 50

new_lat = start[0] + (end[0] - start[0]) * (int(pct_travelled) / 100)
new_lon = start[1] + (end[1] - start[1]) * (int(pct_travelled) / 100)

print(f"Your current location is {new_lat}, {new_lon}")

distance_travelled_so_far = GD(start, (new_lat, new_lon)).km
distance_still_to_travel = GD((new_lat, new_lon), end).km

print(f"You have travelled {distance_travelled_so_far} km")
print(f"You have {distance_still_to_travel} km left to travel")

运行后得到错误结果：

5529.689905151459 km between Paris and New York
Your current location is 44.78475, 38.178399999999996
You have travelled 2744.973813842307 km
You have 2943.5970959509054 km left to travel

错误原因是地球是椭球体，经纬度的每一度对应的实际距离并不均匀，直接线性插值经纬度得到的点并不是球面上两点间大圆弧的中点，因此50%行程时已行驶距离和剩余距离不相等。请问如何用geopy或其他Python库正确实现该功能？

方法一：使用geopy内置的destination方法 #

geopy的geodesic对象提供了destination方法，可以直接计算从起点出发，沿指定方位角移动指定距离后的位置，完全符合球面大圆弧的计算逻辑：

from geopy.distance import geodesic as GD

start = (48.8567, 2.3508)  # Paris
end = (40.7128, 74.0060)  # New York

# 计算起点到终点的总距离和初始方位角
total_distance = GD(start, end)
bearing = GD(start, end).bearing

pct_travelled = 50
travel_distance = total_distance.km * (pct_travelled / 100)

# 获取移动后的位置
current_loc = GD(start).destination(bearing=bearing, kilometers=travel_distance)
new_lat, new_lon = current_loc.latitude, current_loc.longitude

print(f"{total_distance.km} km between Paris and New York")
print(f"Your current location is {new_lat}, {new_lon}")

travelled = GD(start, (new_lat, new_lon)).km
remaining = GD((new_lat, new_lon), end).km

print(f"You have travelled {travelled} km")
print(f"You have {remaining} km left to travel")

运行后，50%行程时的已行驶距离和剩余距离会基本相等（仅存在极小的浮点精度误差）。

方法二：使用pyproj库（更底层的椭球体计算） #

如果需要更灵活的地理计算，可以用pyproj的Geod类，基于WGS84椭球体进行精确的球面计算：

from pyproj import Geod
from geopy.distance import geodesic as GD

start = (48.8567, 2.3508)  # Paris (纬度, 经度)
end = (40.7128, 74.0060)  # New York (纬度, 经度)

# 初始化WGS84椭球体的Geod对象
geod = Geod(ellps='WGS84')

# 计算起点到终点的正向方位角、反向方位角和总距离（单位：米）
forward_az, _, total_dist_m = geod.inv(start[1], start[0], end[1], end[0])
total_dist_km = total_dist_m / 1000

pct_travelled = 50
travel_dist_m = total_dist_m * (pct_travelled / 100)

# 计算移动后的位置（返回值为：经度, 纬度, 最终方位角）
new_lon, new_lat, _ = geod.fwd(start[1], start[0], forward_az, travel_dist_m)

print(f"{total_dist_km} km between Paris and New York")
print(f"Your current location is {new_lat}, {new_lon}")

travelled = GD(start, (new_lat, new_lon)).km
remaining = GD((new_lat, new_lon), end).km

print(f"You have travelled {travelled} km")
print(f"You have {remaining} km left to travel")

这个方法的计算逻辑和geopy一致，但提供了更多自定义椭球体的选项，适合复杂地理场景。

内容的提问来源于stack exchange，提问作者Super