python - 为什么pyephem sublat和STK LLA的结果不同？

Question

    import ephem

    line1 = "WorldView 4"
    line2 = '1 41848U 16067A   20074.82580014 -.00000094  00000-0  00000+0 0  9999'
    line3 = "2 41848  97.8435 176.0145 0008992 126.7749 233.3766 15.40359612182266"
    iss = ephem.readtle(line1, line2, line3)
    iss.compute('2020/3/15 04:00:00.000')
    issE = iss.elevation.real/1000
    print("%s,%s,%s"%(iss.sublat,iss.sublong,issE))

82:05:50.5,-140:07:20.6,453.627375
但是在STK LLA报告中，结果是:
15 Mar 2020 04:00:00.000 82:08:46.1243 N 140:07:21.4394 W 453.625591.特别是在某些纬度，差异变得更大。

Answer 1

STK 提供了每个字段的定义:

https://help.agi.com/stk/11.0.1/Subsystems/dataProviders/Content/Satellite~LLA_State~Fixed.htm

它不计算真实的地理纬度。相反，它只是计算卫星和地球 xy 平面之间的角度:

Lat The detic latitude (i.e., angle between the detic subpoint's surface normal vector and the XY plane.)

地理纬度和地理纬度仅在赤道处一致，两者均为 0°，而在极点处均为 90°。您可以在此处了解有关差异的更多信息:

https://en.wikipedia.org/wiki/Latitude#Geodetic_and_geocentric_latitudes