最近30从www.hoelymoley.com 2023 - 07 - 07 - t18:07:16z //www.hoelymoley.com/feeds/question/14670 https://creativecommons.org/licenses/by-sa/4.0/rdf //www.hoelymoley.com/q/14670 7 pr1268 //www.hoelymoley.com/users/7505 2018 - 07 - 22 - t22:06:58z 2018 - 07 - 25 - t02:12:46z

< p >地球的半径通常是作为6378137米(< a href = " https://en.wikipedia.org/wiki/Earth_radius # Global_average_radii”rel = " noreferrer " > < / >)赤道半径,其压扁是<强> < /强>定义为< a href = " https://en.wikipedia.org/wiki/Flattening # Numerical_values_for_planets”rel = " noreferrer " > 1/298.257223 < / > (WGS84),因此其极半径计算< em > < / em >为< a href = " https://en.wikipedia.org/wiki/Earth_radius # Polar_radius”rel = " noreferrer " > < / > 6356752米。然而,< / p > < p >地球海洋的平均深度是< a href = " https://www.google.com/search?q = % 20的平均% 20深度% 20所有% 20大洋noreferrer“rel = > < / > 3688米(即平均海平面以下3688米),和所有土地的平均身高高于海洋< a href = " https://www.quora.com/What-is-the-average-elevation-of-Earth-above-the-ocean-including-land-area-below-sea-level-What-is-the-atmospheric-pressure-at-that-elevation " rel = " noreferrer " > < / > 840米。< / p > < p >假设< a href = " https://hypertextbook.com/facts/1997/EricCheng.shtml " rel = " noreferrer " > 71%的海洋和陆地< / > 29%,这给了< / p > < p > 0.71美元\ * (-3688 ~ {\ rm m}) ~ + ~ 0.29 \乘以840 ~ {\ rm m} ~ = ~ -2374.8 ~ {\ rm m} $。换句话说,2374.8米以下(当前)平均海平面将地球“台球”如果所有的海洋都耗尽了< /一口> <一口> 1。< / p > < p >,我的问题是:< / p > < p > <强>的定义高程测量地球的半径是多少?< /强>台球海拔,目前的平均海平面,还是别的?< / p > < p > <一口> 1 < / >共舞,当然,这忽略了扁率造成的压扁和所有的起伏所描述的< em > < a href = " https://en.wikipedia.org/wiki/Geoid " rel = " noreferrer " >大地水准面< / > < / em >。< / p >

//www.hoelymoley.com/questions/14670/-/14684 # 14684 5 大卫Hammen //www.hoelymoley.com/users/239 2018 - 07 - 25 - t02:06:32z 2018 - 07 - 25 - t02:12:46z

< p >最初,参考椭球的概念是一个椭球,最佳近似平均海平面。这个概念早于卫星大地测量数百年。现在有更好的椭圆体的提供一个更好的适合比WGS84椭球平均海平面。然而,WGS84椭球使用全球(包括可笑晋升压扁值)。< / p > < p >现在WGS84参考椭球,参考椭球(也就是说,它是由GPS椭球用作参考和相关系统)。1993年WGS84管理委员会投票,但有一个例外,保留1984定义的值,尽管改进这些定义的值。压扁的一个例外:WGS84的原始定义是一个计算值,基于地球的第二个动态形式确定卫星轨道(美元\酒吧C_ {2 0} $ WGS84, J_2 GRS80)美元。这个计算值在1993年成为一个定义值。保持这些旧值是全球定位系统(GPS)的原因。最好有一个参考椭球体是常数随时间比最适合椭球不断改善。< / p > < p >此外,并不是所有的变化最适合椭球代表减少测量误差。 The best fit ellipsoid truly does change over time as the Earth continues to recover from the last glaciation and as the Earth's rotation rate slows down. There are very few applications where a best fit ellipsoid truly is needed while there are many applications where a constant reference ellipsoid is the "best fit".

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