[OpendTect_Users] GNSS coordinates, Decimal degree

[Maurizio Ercoli]

Dear all,

I'm sorry for my late reply, thanks to all for your advices.

Here below you can find a link to download a test SEG-Y file, with two
ascii files containing the coordinates (also in WGS84 UTM zone 33 N).

https://dl.dropboxusercontent.com/u/37804219/Lsf_300.zip

I can export directly UTM coordinates from my acquisition software with a
cm/mm resolution, but then I can't import e.g.

0    607778.360    4404971.106    33S    384.77

Dr. Julien Moreau highlights the real problem, I think..thanks.

A Odt tool (the 2D geometry works in this way?), that allows to directly
load the coordinates from the ascii files, could be really useful and it
can be a simple solution to that problem (e.g. also using a scalar like
1000). In this way, you could import the coordinates in Odt without
directly read into the SEG-Y file...also in the case of numerous and long
2D lines and/or 3D GPR volume.

Anyway, other solutions?

thanks to all, one more time.

best regards

Maurizio




2014-01-30 Julien Moreau <julien.moreau at ign.ku.dk>:

>  Dear all,
>
> I am sorry to say that it is not possible to always attain GPR precision
> with the SEGY format in some of the orthometric projections.
> The computing arithmetics says that you can store in a signed 4 byte
> integer the values:
> -2 147 483 648 to 2 147 483 647
> You may be familiar with the false northing and the false easting that you
> add to your local projection.
> These values are of the order of millions
> I take the worst case scenario where in Finland there is a false easting
> which is associated with a band number from 1 to 6 on top of that
> so you have a number like 5 123 123
> You want 3 digits precision and because that is what is the precision in
> GPR profiling thus it is written in your SEGY:
> 5 123 123 123
> with a coefficient -1000 (i.e. scalar coordinates trace header bytes 71-72)
> Well in fact you cannot do that so according to your processing software
> it will raise an error or not. And you don't want to know how the rounding
> is made, it is at bit level so...
> For other reasons the vertical sampling rate does not like to have too
> many decimals. So when you convert your profiles in depth you have weird
> things going on.
> I use OdT since many years in seismics or GPR and I really advise 2 things:
> Add yourself a coeff of 100 or 1000 on your coordinates (in 3D: xyz)
> Extract your navigation with your processing software and import it in
> manage 2D geometry. The OdT 2D geometry can swallow anything as far as I
> have observed.
> just a reminder, all concepts are not exchangeable between geophysical
> methods and numerics have limitations,
>
> Regards,
>
>
> Julien
>
>
>   Julien Moreau, PhD
> Assistant Professor, Applied Geophysics
> Department of Geosciences and Natural Resource Management
> University of Copenhagen,
> Øster Voldgade 10, 1350 København, Denmark
> Office: +45 21 28 86 34
>
>
>  ------------------------------
> *From:* users-bounces at opendtect.org [users-bounces at opendtect.org] on
> behalf of Alessandro Menichino [alessandro.menichino at gmail.com]
> *Sent:* 29 January 2014 11:17
> *To:* Maurizio Ercoli
> *Cc:* users at opendtect.org
> *Subject:* Re: [OpendTect_Users] GNSS coordinates, Decimal degree
>
>  Hi Maurizio,
> I use opendtect for seismic interpretation, if you have a non projected
> coordinates OPD use them as projected coordinates. One walk-aroud is could
> be to use a scalar during the import of data, so you don't have a lot od
> decimal digit.
> try to send me the survey folder (only for the settings of the area) and
> one sgy file.
>
>  Berst regards,
> Alessandro
>
>  Il giorno 28/gen/2014, alle ore 19:01, Maurizio Ercoli <
> maurizio.ercoli at gmail.com> ha scritto:
>
>  Dear all,
>
> I'm using OpendTect for the interpretation of GPR data, and I have
> coordinates recorded with a GNSS system, having centimetric accuracy.
>
> I can't import correctly the decimal degrees in ODT, someone can help me?
>
> I can also upload a SEG-Y file, if you need it...
>
> Thank you in advance.
>
>  Best regards,
>
>  M.
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