在 2015年4月20日星期一 UTC+2下午7:59:24，ale...@gmail.com写道：

Thank you for the response Alexander. It looks as though the elevation conversion requires a lookup table in a 3.3MB file rather than a stand-alone formula. I was hoping to implement the conversion entirely on the browser side which would mean always downloading the Geoid height file. Do you know if this is my only option?

Thanks,

Alec.

> Hi Alec,

>

>

> The terrain elevations in Cesium are relative to the WGS84 ellipsoid. You can use the EGM96 geoid for a global MSL approximation to sample geoid heights relative to the WGS84 ellispoid, see here:

>

>

> http://earth-info.nga.mil/GandG/wgs84/gravitymod/egm96/egm96.html

>

>

> Alex

>

>

> Hi Alexander,

>

>

>

>

>

> Could you tell me the formula you used to figure out the 47m delta between sea level and the cesium representation of 0 elevation at the latitude of the specific area.

>

>

>

> I need to be able to put buildings on the map at the visually correct elevation any where in the world so I need to factor the latitude into the calculation.

>

>

>

> Thank you,

>

> Alec.

>

>

>

>

>

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>

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在 2015年4月20日星期一 UTC+2下午7:59:24，ale...@gmail.com写道：

Thank you for the response Alexander. It looks as though the elevation conversion requires a lookup table in a 3.3MB file rather than a stand-alone formula. I was hoping to implement the conversion entirely on the browser side which would mean always downloading the Geoid height file. Do you know if this is my only option?

Thanks,

Alec.

> Hi Alec,

>

>

> The terrain elevations in Cesium are relative to the WGS84 ellipsoid. You can use the EGM96 geoid for a global MSL approximation to sample geoid heights relative to the WGS84 ellispoid, see here:

>

>

> http://earth-info.nga.mil/GandG/wgs84/gravitymod/egm96/egm96.html

>

>

> Alex

>

>

> Hi Alexander,

>

>

>

>

>

> Could you tell me the formula you used to figure out the 47m delta between sea level and the cesium representation of 0 elevation at the latitude of the specific area.

>

>

>

> I need to be able to put buildings on the map at the visually correct elevation any where in the world so I need to factor the latitude into the calculation.

>

>

>

> Thank you,

>

> Alec.

>

>

>

>

>

> --

>

> You received this message because you are subscribed to the Google Groups "cesium-dev" group.

>

> To unsubscribe from this group and stop receiving emails from it, send an email to cesium-dev+...@googlegroups.com.

>

> For more options, visit https://groups.google.com/d/optout.

Hi Alec,

I think the difference of elevation between geoid and sea level comes from the nature of earth itself (http://en.wikipedia.org/wiki/Geoid ), so it may not be possible to "calculate" it by formulas or so. If you worry about the 3.3MB extra downloads, preprocessing your data may be the best way to go. Another possible approach may be to set up a geoid server and just query for the area in the view dynamically.

Best,

Anran