Re: GRDGRADIENT

Hi,

I am trying use grdcut around the center latitude/longitude of -15.5/-71.5 as below:


grdcut slabsurf2.grd -Gslabcut.grd -R-15.6/-15.4/-71.6/-71.4 -V


But I am getting the following error:

grdcut: Subset exceeds data domain!


I run grdinfo to check the range of my slab grid file:

grdinfo slabsurf2.grd

slabsurf2.grd: x_min: -82 x_max: -66 x_inc: 0.0744186046512 name: x nx: 216
slabsurf2.grd: y_min: -20 y_max: -9 y_inc: 0.0718954248366 name: y ny: 154

I couldn't understand why the grdcut is giving this error. I would be grateful for any suggestions.

Thanks
Abhash kumar
________________________________
From: World-Wide GMT Usage and Help Mailing List <[email protected]> on behalf of Paul Wessel <[email protected]>
Sent: Thursday, February 20, 2014 5:12 PM
To: [email protected]
Subject: Re: [GMT-HELP] GRDGRADIENT

I cannot tell if anything is wrong here.  You would have to show based on your data that these strikes are wrong; then we could debug and see what might be going wrong.  Since you "know" the strike might be 30-120, pick a point where you know it should be ~100 and see what grdgradient says.  If there is stark disagreement, use grdcut to cut out a tiny grid (say 5x5 nodes) centered on that value from your grid, rerun grdgradient on this grid to confirm there is a mismatch, and post it as a potential bug on the gmt website.

Cheers, Paul

On Feb 20, 2014, at 11:50 AM, Mr Abhash Kumar <[email protected]<mailto:[email protected]>> wrote:

Hi,
I used grdgradient to calculate the strike of downdip direction at every grid point of the subducting slab:

grdgradient slabsurf2.grd -Dn -Sslabgradient.grd -M -V

I am getting the following results:

-69.9441860465  -17.0522875817  35.6361160278
-69.8697674419  -17.0522875817  36.5936279297
-69.7953488372  -17.0522875817  37.6132316589
-69.7209302326  -17.0522875817  38.6617622375
-69.6465116279  -17.0522875817  34.4591636658
-69.5720930233  -17.0522875817  31.943397522
-69.4976744186  -17.0522875817  31.6246490479
-69.423255814   -17.0522875817  30.8437995911

I roughly know that the strike of downdip direction should vary in the range of 30degree-120 degree in this region. Do I need to use some more functions to calculate the reasonable strike direction. I urgently need to calculate this and would be extremely grateful for any suggestions.

Thanks
Abhash kumar
University of North Carolina at Chapel Hill
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