< p >技术是的,但实际上,通常没有。< / p > < p >三维磁场变化和不平行于地球表面的变化。然而,横向距离变化通常在更大的规模比海拔和日常使用,偏差仅基于水平位置。< / p > < p >普通地球磁场模型,< a href = " http://earth -行星space.springeropen.com/articles/10.1186/s40623 - 015 - 0228 - 9”> IGRF-12 < / >(国际地磁参考场)使用径向距离地球的中心< em > < / em > (r)与地球意味着传统地磁参考球面半径< em > < / em >。换句话说,海拔。< em > (a / r) < / em >通常会几乎是< em > < / em > 1,和差异小于其他测量的不确定性,如偏差由于磁异常< a href = " https://en.wikipedia.org/wiki/Magnetic_anomaly " > < / >。< / p > < p >计算磁场通常是通过使用< a href = " https://www.ngdc.noaa.gov/IAGA/vmod/igrf12coeffs.txt " >出版模型< / >和< a href = " https://www.ngdc.noaa.gov/IAGA/vmod/igrf12.f " > < / >代码。正如你所看到的(代码相当容易阅读),磁场垂直分量用于估计为每一个位置。< / p > < p >在线计算器通常用于纠正偏差用于导航:< / p > < ul > <李> < p > < a href = " https://www.ngdc.noaa.gov/geomag-web/?模型= igrf " > NOAA的< / >计算器不包括海平面高度和计算。李李< / p > < / > < > < p > < a href = " http://www.geomag.bgs.ac.uk/data_service/models_compass/igrf_form.shtml " >英国地质调查局的< / >和< a href = " http://www.ga.gov.au/oracle/geomag/agrfform.jsp " > GA的< / >计算器,但海拔有一个小对偏差的影响。 Try it to see! Simpler models, e.g the dipol model also suggest how the magnetic declination varies with distance from the Earth's magnetic center. The approximation work rather well at low latitudes and at the Earth's surface. It can also be used to model Earth's magnetic field in an astronomical context.
Apart from declination, there is also an inclination to take into account. Near the magnetic poles, the compass needle will not be horizontal, but get a dip. This can make normal field compasses almost useless near the magnetic poles (trust me, I tried..).