Several versions of the EGM96 grid

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Several versions of the EGM96 grid

Kristian Evers-2

All,

 

Just a word of caution. It has recently come to my attention that there’s in fact several versions of the egm96_15.gtx grid being distributed. Thomas discovered it whilst trying to debug some failing tests. One version of the grid is distributed with OSGeo4W and the other is distributed on the OSGeo download website: http://download.osgeo.org/proj/vdatum/egm96_15/egm96_15.gtx

 

It is not clear to me which of the two versions of the grid is the correct one, but it is obvious that they are different. The image at https://i.imgur.com/eG80Wv5.jpg  shows the difference between the two grids (download.osgeo.org - OSGeo4W). There is upwards of a meters difference in some places. Quite significant, and potentially a problem for some users. In the OSGeo4W-grid the grid values seem to be limited to two decimals, whereas the other grid has more decimal places (4-7, normal floating point behavior). I have a suspicion that the two grids are offset slightly in the east-west direction, but haven’t been able to confirm it.

 

Has anyone on the list got any insight as to which of the two versions of the grid is the correct one?

 

Cheers,

Kristian


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Re: Several versions of the EGM96 grid

Andre Joost
Am 05.10.2017 um 10:34 schrieb Kristian Evers:

> All,
>
> Just a word of caution. It has recently come to my attention that
> there's in fact several versions of the egm96_15.gtx grid being
> distributed. Thomas discovered it whilst trying to debug some failing
> tests. One version of the grid is distributed with OSGeo4W and the
> other is distributed on the OSGeo download website:
> http://download.osgeo.org/proj/vdatum/egm96_15/egm96_15.gtx
>
>
> Has anyone on the list got any insight as to which of the two
> versions of the grid is the correct one?
>

If you look at:

http://download.osgeo.org/proj/vdatum/egm96_15/

You see a egm96_15-incorrect.gtx from 2010, and a "correct" one from 2014.

OSGEO4W64 has the one from 2010.

HTH,
andré Joost



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Re: Several versions of the EGM96 grid

Andre Joost
Am 05.10.2017 um 11:31 schrieb Andre Joost:

> If you look at:
>
> http://download.osgeo.org/proj/vdatum/egm96_15/
>
> You see a egm96_15-incorrect.gtx from 2010, and a "correct" one from 2014.
>
> OSGEO4W64 has the one from 2010.
>

And the related ticket is .....:

https://github.com/OSGeo/proj.4/issues/126

So soemone should update the OSGEO4W file as well.

Greetings,
André Joost


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Re: Several versions of the EGM96 grid

Kristian Evers-2
Andre,

Well that clears that up. I see that you have already create a ticket with the OSGeo4W guys. Thanks!

/Kristian

-----Oprindelig meddelelse-----
Fra: [hidden email] [mailto:[hidden email]] På vegne af Andre Joost
Sendt: 5. oktober 2017 11:38
Til: [hidden email]
Emne: Re: [Proj] Several versions of the EGM96 grid

Am 05.10.2017 um 11:31 schrieb Andre Joost:

> If you look at:
>
> http://download.osgeo.org/proj/vdatum/egm96_15/
>
> You see a egm96_15-incorrect.gtx from 2010, and a "correct" one from 2014.
>
> OSGEO4W64 has the one from 2010.
>

And the related ticket is .....:

https://github.com/OSGeo/proj.4/issues/126

So soemone should update the OSGEO4W file as well.

Greetings,
André Joost


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Re: Several versions of the EGM96 grid

J Luis
And why still use the EGM96 instead of at least the EGM2008?

Joaquim

Sent from my iDedo

No dia 05/10/2017, às 10:56, Kristian Evers <[hidden email]> escreveu:

> Andre,
>
> Well that clears that up. I see that you have already create a ticket with the OSGeo4W guys. Thanks!
>
> /Kristian
>
> -----Oprindelig meddelelse-----
> Fra: [hidden email] [mailto:[hidden email]] På vegne af Andre Joost
> Sendt: 5. oktober 2017 11:38
> Til: [hidden email]
> Emne: Re: [Proj] Several versions of the EGM96 grid
>
>> Am 05.10.2017 um 11:31 schrieb Andre Joost:
>>
>> If you look at:
>>
>> http://download.osgeo.org/proj/vdatum/egm96_15/
>>
>> You see a egm96_15-incorrect.gtx from 2010, and a "correct" one from 2014.
>>
>> OSGEO4W64 has the one from 2010.
>>
>
> And the related ticket is .....:
>
> https://github.com/OSGeo/proj.4/issues/126
>
> So soemone should update the OSGEO4W file as well.
>
> Greetings,
> André Joost
>
>
> _______________________________________________
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> [hidden email]
> http://lists.maptools.org/mailman/listinfo/proj
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Re: Several versions of the EGM96 grid

Kristian Evers-2
Joaquim,

In case you have some dataset that is defined in terms of EGM96 that you want to convert to something else, for instance.

In this particular case I have been using the egm96_15.gtx file for testing various grid-shifting operations for the vertical component in PROJ.4. I use the EGM96 grid because it is readily available in most grid distributions. Something that cannot be said about EGM2008 (i.e. not part of the OSGeo vdatums package).

/Kristian

-----Oprindelig meddelelse-----
Fra: [hidden email] [mailto:[hidden email]] På vegne af Joaquim Luis
Sendt: 5. oktober 2017 12:58
Til: PROJ.4 and general Projections Discussions <[hidden email]>
Emne: Re: [Proj] Several versions of the EGM96 grid

And why still use the EGM96 instead of at least the EGM2008?

Joaquim

Sent from my iDedo

No dia 05/10/2017, às 10:56, Kristian Evers <[hidden email]> escreveu:

> Andre,
>
> Well that clears that up. I see that you have already create a ticket with the OSGeo4W guys. Thanks!
>
> /Kristian
>
> -----Oprindelig meddelelse-----
> Fra: [hidden email] [mailto:[hidden email]] På vegne af Andre Joost
> Sendt: 5. oktober 2017 11:38
> Til: [hidden email]
> Emne: Re: [Proj] Several versions of the EGM96 grid
>
>> Am 05.10.2017 um 11:31 schrieb Andre Joost:
>>
>> If you look at:
>>
>> http://download.osgeo.org/proj/vdatum/egm96_15/
>>
>> You see a egm96_15-incorrect.gtx from 2010, and a "correct" one from 2014.
>>
>> OSGEO4W64 has the one from 2010.
>>
>
> And the related ticket is .....:
>
> https://github.com/OSGeo/proj.4/issues/126
>
> So soemone should update the OSGEO4W file as well.
>
> Greetings,
> André Joost
>
>
> _______________________________________________
> Proj mailing list
> [hidden email]
> http://lists.maptools.org/mailman/listinfo/proj
> _______________________________________________
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Re: Several versions of the EGM96 grid

stevejking
Joaquim
Also EGM96 is the geoid specified in the KML2.2 specification.
Steve



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