問題描述

我試圖找到如何使海拔高于平均海平面.此時，它從橢球返回高度.所以，任何人都知道改變高度值的公式或計算從橢球到平均海平面的高度值.

I tried to find how to get the altitude above the mean sea level. At this time, it returns altitude from the ellipsoid. So, anyone knows the formula or calculation to change the altitude value from ellipsoid to the altitude value from mean sea level.

感謝大家的幫助

推薦答案

正如你提到的，GPS 返回高度作為與 WGS84 參考橢球的偏移量，但大多數人希望看到平均海平面 (MSL)，而這兩個經常不同意.最常用的方法是在表格中查找 delta，然后根據 GPS 的高度和表格中的 delta 使用它來計算 MSL.

As you mentioned, GPS returns the altitude as an offset from the WGS84 reference ellipsoid, but most people want to see mean sea level (MSL), and the two frequently don't agree. The way this is most frequently done is by looking up the delta in a table and using that to compute MSL based on the height from GPS and the delta in the table.

這里有一些java代碼:https://github.com/NASAWorldWind/WorldWindJava/blob/develop/src/gov/nasa/worldwind/util/EGM96.java.它使用 Worldwind 的其他功能并沒有那么復雜，因此您可能可以使用大部分未修改的代碼，如果您使用 Java 并且它們的許可證滿足您的需求，則可以調整其余代碼.

There's some java code here: https://github.com/NASAWorldWind/WorldWindJava/blob/develop/src/gov/nasa/worldwind/util/EGM96.java. The other functions that it uses from Worldwind aren't that complicated, so you could probably use most of the code unmodified, and the rest you could adapt if you're working in Java and their license meets your needs.

它使用來自 EGM 96 數據集的信息(鏈接這里如果您有興趣-- 不是絕對必要的)，你可以在這里下載:https://github.com/jleppert/egm96/blob/master/WW15MGH.DAC.您將需要 WW15MGH.DAC 文件.它是一個包含 16 位有符號整數的二進制文件.您可以使用 Java 示例向您展示如何訪問文件中的數據.如果那是您的事，他們還提供了一個 Fortran 示例.:-)

It uses information from the EGM 96 data set (link here if you're interested -- not strictly necessary though), which you can download here: https://github.com/jleppert/egm96/blob/master/WW15MGH.DAC. You will want the WW15MGH.DAC file. It's a binary file full of 16-bit signed integers. You can use the Java example to show you how to access the data in the file. They also provide a Fortran example if that's your thing. :-)

這是他們自述文件中的文件信息.

Here's the information on the file from their readme.

15 分鐘全球二元大地水準面高度文件的數據說明:

Data Description for 15 minute worldwide binary geoid height file:

---- 文件:WW15MGH.DAC

---- FILE: WW15MGH.DAC

文件的總大小為 2,076,480 字節.該文件已創建使用 INTEGER2 數據類型格式并且是未格式化的直接訪問文件.文件中的數據從北到南排列在記錄中.文件中有 721 條記錄，從 90 N 處的記錄 1 開始.文件上的最后一條記錄位于南緯 90 度.對于每條記錄，有是 1,440 個 15 弧分的大地水準面高度，按經度從西到東從本初子午線 (0 E) 到西邊 15 角分本初子午線 (359.75 E).在文件中，大地水準面高度以單位為單位厘米.在檢索文件中的 Integer2 值時，除以100，這將產生一個以米為單位的大地水準面高度.

The total size of the file is 2,076,480 bytes. This file was created using an INTEGER2 data type format and is an unformatted direct access file. The data on the file is arranged in records from north to south. There are 721 records on the file starting with record 1 at 90 N. The last record on the file is at latitude 90 S. For each record, there are 1,440 15 arc-minute geoid heights arranged by longitude from west to east starting at the Prime Meridian (0 E) and ending 15 arc-minutes west of the Prime Meridian (359.75 E). On file, the geoid heights are in units of centimeters. While retrieving the Integer2 values on file, divide by 100 and this will produce a geoid height in meters.

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