Re: Gravity effect of a layer

> I tried a small region and the program ran; clearly it was working on 
> the big grid but very very slowly!

Yes, it is slow but one often do not need to compute with a very high 
resolution. Bhattacharyya prisms would be a bit faster but probably not 
that much

> The output is very much affected by boundary effects. There is no way 
> to set a larger dimension to work in other than cut a larger grid 
> area to process and set a region of interest (-R).  With grdfft etc we 
> can set a -N option to force a larger dimension, but not here.

Yes, there is. See option -Q (documented) and the, sorry my fault, the 
-R option that is only mentioned on the on line help

>  Given that this is a small region, the gravity signal computed seems 
> rather large? The thickness range is 3600-10400m.

They looks perfectly reasonable values. A max of ~700 mGal compare very 
well with the Bouger plate that gives (with you density)

  2*pi*2000*6.67e-11*10000*1e5 = 838 mGal

>
> Attached a quick image of the original data and output.
>
> Cheers
> Lester
>
> ------------------------------------------------------------------------
> Date: Wed, 12 Mar 2014 07:45:33 -1000
> From: [email protected]
> Subject: Re: [GMT-HELP] Gravity effect of a layer
> To: [email protected]
>
> Is there a -Vl option to see progress? If not then please add.
>
> Sent from my iPad
>
> On Mar 12, 2014, at 6:29 AM, "J. Luis" <[email protected] 
> <mailto:[email protected]>> wrote:
>
>     Lester,
>
>     grdgravmag3d is a slow program (it computes the effect of all the
>     triangles (two per cell) at all the nodes of the destination
>     grid), and your grid isn't exactly small (in terms of grdgravmag3d
>     reference frame)
>     Are you sure it hanged? The processor was working at 100%?
>     Can you cut a smaller piece of the grid and try again? If it still
>     hangs open an issue in the gmtrac page and append the file so that
>     we can debug it.
>
>     Joaquim
>
>         Hello,
>
>         I have a grid of sediment thickness data and would like to
>         correct the gravity data for this.
>
>         I have looked at grdgravmag3d and this should be fine, but
>         when I tried this route it gets stuck:
>
>         grdgravmag3d -C2000 -GSeds_thick_clipped_grav.grd -V -fg
>         Sediment_thickness_clipped.grd -I1m -Z
>         grdgravmag3d: Grid dimensions are nx = 2581, ny = 1441
>         grdgravmag3d: Allocates memory and read data file
>         Line = 0         of = 1441 <----- hangs here!
>
>         What I am looking to do is a sediment corrected Bouguer.
>
>         Any pointers would be useful.
>
>         Thanks
>         Lester
>
>
>         To unsubscribe, send the message "signoff gmt-help" to
>         [email protected] <mailto:[email protected]> 
>
>
>     To unsubscribe, send the message "signoff gmt-help" to
>     [email protected] <mailto:[email protected]>
>
> To unsubscribe, send the message "signoff gmt-help" to 
> [email protected]
> To unsubscribe, send the message "signoff gmt-help" to 
> [email protected] 


To unsubscribe, send the message "signoff gmt-help" to [email protected]