Re: Gravity effect of a layer

Hi Joaquim, Paul,
 
I tried a small region and the program ran; clearly it was working on the big grid but very very slowly!
 
I assume that thicknesses must be in meters so Im scaled the original km grid and tested a small 2x2 degree area:
 
grdgravmag3d -C2000 -Gtest_layer_grav.grd -Vl -fg test_invert2.grd -I1m
grdgravmag3d: Geographic grid, longitudes span less than 360
grdgravmag3d: Geographic grid, longitudes span less than 360
grdgravmag3d: Chosen boundary condition for all edges: geographic
grdgravmag3d: Grid dimensions are nx = 121, ny = 121
grdgravmag3d: Allocates memory and read data file
grdgravmag3d: Reading grid from file test_invert2.grd
grdgravmag3d: packed z-range: [3606.04,10434.4]
grdgravmag3d: Geographic grid, longitudes span less than 360
grdgravmag3d: Chosen boundary condition for all edges: geographic
grdgravmag3d: Set boundary condition for all edges: natural
grdgravmag3d: Set boundary condition for left   edge: natural
grdgravmag3d: Set boundary condition for right  edge: natural
grdgravmag3d: Set boundary condition for bottom edge: natural
grdgravmag3d: Set boundary condition for top    edge: natural
grdgravmag3d: Writing grid to file test_invert1_layer_grav.grd
grdgravmag3d: packed z-range: [-796.454,-84.6499]
 
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.
 
Given that this is a small region, the gravity signal computed seems rather large? The thickness range is 3600-10400m.
 
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]> 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

         

         

      
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