RE: SRTM vertical datum confirmation - geoid or ellipsoid???

[matthew zengerer]

try again, failed last time

Matthew Zengerer
Consulting Geophysicist
Adelaide, SA
+61 8 7127 9937 (H)
+61 (0) 4 0674 8819 (M)

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From: mzen...@hotmail.com
To: cgia...@googlegroups.com
Subject: SRTM vertical datum confirmation - geoid or ellipsoid???
Date: Wed, 26 Oct 2011 18:48:06 +1030

Hello CGIAR,

Perhaps this sort of question would normally go in a FAQ area

I just wish to double check: SRTM ascii data are in the EGM96 geoid vertical datum, NOT WGS84 ellipsoidal datum??

Checking back to NASA website it specifies EGM96 but I have seen other papers talking about ellipsoidal SRTM heights

The .prj files say spheroid:WGS84

Does that definitely mean we are talking about a geoid or an ellipsoid??

As WGS84 can be both?!!

Can someone please confirm the reality of where the data lie, and please consider altering the README files so they are a bit more specific

Obviously very important to be aware of!!!

Thankyou for the wonderful data in the meantime they are extremely helpful.

Best Regards

Matthew Zengerer
Consulting Geophysicist
Adelaide, SA
+61 8 7127 9937 (H)
+61 (0) 4 0674 8819 (M)

[Antonio Trabucco]

Hi Matthew,
the EGM96 is an official Earth Gravitational Model adopted within the WGS84 World Geodetic System.
The original Earth gravitation Model for WGS84 was EGM84, from 1996 until 2008?? (Not sure) EGM96 was adopted. I believe that after 2008 there is a newer EGM.

There is no conflict, EGM is simply a refinement of the WGS. Antonio
________________________________________
From: cgia...@googlegroups.com [cgia...@googlegroups.com] On Behalf Of matthew zengerer [mzen...@hotmail.com]
Sent: Wednesday, October 26, 2011 10:24 AM
To: cgia...@googlegroups.com
Subject: [CGIAR-CSI] RE: SRTM vertical datum confirmation - geoid or ellipsoid???

Hello CGIAR,

Best Regards

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[matthew zengerer]

Dear Antonio, 

Thank you very much for taking the time to reply to my email.

I'm afraid it doesn't answer my question though, which is:

Are the CGIAR SRTM digital elevation data ellipsoidal or geoidal heights?

Thanks once again

Best Regards 

Matt

Matthew Zengerer
Consulting Geophysicist
Adelaide, SA
+61 8 7127 9937 (H)
+61 (0) 4 0674 8819 (M)

[Antonio Trabucco]

sorry Matthew, now I fully understand your question.
Indeed it is a question that only people that have processed the SRTM database (Andy??) may confirm..... I am curious too. Cheers

________________________________________
From: cgia...@googlegroups.com [cgia...@googlegroups.com] On Behalf Of matthew zengerer [mzen...@hotmail.com]

Sent: Thursday, October 27, 2011 1:49 AM
To: cgia...@googlegroups.com

[matthew zengerer]

Yes, there is a conflict between what it says on the NASA description of SRTM3 and what it says in the .prj files of the CGIAR data.

I think others are taking the CGIAR SRTM as ellipsoid when it may in fact be geoid.

Some clarification from CGIAR is required

Thanks!!

Matt Z

[Jawoo]

Matthew - Here is Andy's message for you (He somehow had problem posting this message to the group):

******

Matthew,

Many thanks for insisting on this one.  I had a look into it, and you are right!  It should be geoid.

We'll correct the metadata..

Andy.

[matthew zengerer]

Hi Andy, Jawoo, Antonio, and CGIAR,

Thanks very much for confirming this for me, it will make things much simpler to reconcile my GPS and terrain corrections!!

Also will very much clarify the situation for everyone who downloads your data.

Thanks!!

Best Regards

Matt Z

Matthew Zengerer
Consulting Geophysicist
Adelaide, SA
+61 8 7127 9937 (H)
+61 (0) 4 0674 8819 (M)

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Date: Thu, 27 Oct 2011 18:20:51 -0700
From: smoo...@gmail.com
To: cgia...@googlegroups.com
Subject: [CGIAR-CSI] Re: SRTM vertical datum confirmation - geoid or ellipsoid???

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