[Proj] Can I convert the ellipsoids using Proj?

[Noel Zinn (cc)]

Cleo,

That’s right.  You’re looking primarily at a 70cm difference in height, but it varies a few centimeters as a function of latitude.  Jose’s instructions should nail it exactly, but I’m not a proj4 expert, so I leave you in the hands of others more knowledgeable.

Noel

Noel Zinn, Principal, Hydrometronics LLC
+1-832-539-1472 (office), +1-281-221-0051 (cell)
noel.zinn at hydrometronics.com (email)
http://www.hydrometronics.com (website)


From: Cleo Drakos 
Sent: Tuesday, August 19, 2014 6:29 PM
To: PROJ.4 and general Projections Discussions 
Subject: Re: [Proj] Can I convert the ellipsoids using Proj?

Dear Noel 

Thanks for your explanation. So it means that both ellipsoids have the same geocentric coordinates, and I can use Jose's instruction.
I have four columns (lats, lons, elevation, and geoid) in an ASCII file. I need to convert all these four parameters into WGS84 system.
How can I apply Jose's instruction? I mean how can I call cs2cs for different parameters? I did not know how to input these four parameters.


Sorry for this type of question, I hope you do not mind.



cleo



On Tue, Aug 19, 2014 at 8:44 PM, Noel Zinn (cc) <ndzinn at comcast.net> wrote:

  Cleo,

  FAQ #7 under Altimetry products in the link you provide seems to answer the question you ask.  The FTP link in that paragraph leads you to  a program top2wgs.pro that solves your problem.  The program assumes dX = dY = dZ = 0.  I’ve made the same assumption myself with TOPEX/Poseidon in a different context.  Then follow Jose’s cs2cs instructions.

  Thanks for the link.

  Noel

  Noel Zinn, Principal, Hydrometronics LLC
  +1-832-539-1472 (office), +1-281-221-0051 (cell)
  noel.zinn at hydrometronics.com (email)
  http://www.hydrometronics.com (website)


  From: Cleo Drakos 
  Sent: Tuesday, August 19, 2014 3:39 AM
  To: PROJ.4 and general Projections Discussions 
  Subject: Re: [Proj] Can I convert the ellipsoids using Proj?

  Dear Jose

  Thanks for your answer. Can you help me how can I make certain that both ellepsoids have the same geocentric coordinates.
  Only the information I am having is below under the section of How does the GLAS ellipsoid compare with WGS 84?


  http://nsidc.org/data/icesat/faq.html#3_all 


  cleo



  On Tue, Aug 19, 2014 at 6:03 AM, Jose Gonçalves <jagoncal at gmail.com> wrote:

    Cleo

    If cartesian geocentric coordinates are the same and you just want to express them in a different ellipsoid you can do:

    cs2cs -f %.9f +a=6378136.30 +rf=298.257 +proj=latlong +towgs84=0,0,0 +to +a=6378137 +rf=298.25722356 +proj=latlong +towgs84=0,0,0


    If there are shift and rotation you can express them in the +towgs84.


    Regards


    José 





    2014-08-18 15:13 GMT+01:00 Cleo Drakos <cleo21drakos at gmail.com>:

      Dear guys,

      I have the data (latitudes, longitudes, and elevations) given in ICESat/GLAS ellipsoid. This equatorial radius and  reciprocal flattening (1/f) on this ellipsoid are 6378136.30 m and is 298.257 respectively.

      Now, I want to convert my data into WGS84 ellepsoid with equatorial radius and reciprocal flattening (1/f) of 6378137.000000 and 298.25722356 respectively.

      Can I convert the ellipsoids using Proj?

      I hope some of you can help me.


      cleo

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