[Manifold-l] Surfer .GRD import

[Pat Waggaman]

Probably data taken in Lat Long and the distances 
properly converted into metres.

Check the data along parallels of Latitude to 
compare.  Points along a higher latitude line 
should have smaller distances between points in 
the grid running EW, than one closer to the 
equator.  The EW distances should relate via the formula cos(lat).

Assuming this is the case, you´d import the data 
and assign it the projection Lat Long in 
Manifold, for that is what the grid really is; 
then you can change the projection as you like.

We did this for the Scripps Gravity dataset back 
in the mid 90´s.  When we got along to 
incorporating Manifold around the turn of the 
century we began the Surfer to Manifold exports, 
due to the superior mapping capability of 
Manifold, wound up with some "gravitic or 
mathematical anomalies" e.g. holes that weren´t 
there in the bottom of the Chilean Fjords.  Just 
saw where the current seismic centers are in the 
spurt of seismic earthquakes in Souther Chile a 
couple of weeks ago, these anomalies were 
actually subterranean magma chambers - gravity 
charting finding the lower density! - and thus we 
were the first to find the volcano which is now 
preparing to erupt in Aisen.  Moral of the story, 
keep the numbers and projections as clear as 
possible, ´cuz the anomalies - can be explosive :)

Cheers,

Pat

At 13:15 03-05-2007, M Roseveare wrote:
>No, the incoming data is in metres, assigned projection is 'orthographic'
>and it comes out squished... I'm not reprojecting to anything either.
>
>
>Martin Roseveare
>Senior Geophysicist
>
>
>Web: www.archaeophysica.co.uk
>Phone: +44 (0) 1989 730 564
>Fax: +44 (0) 7050 369 790
>
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>
>-----Original Message-----
>From: Pat Waggaman [mailto:waggaman at marimsys.com]
>Sent: 03 May 2007 17:53
>To: m.roseveare at archaeophysica.co.uk; manifold-l at directionsmedia.net
>Subject: RE: [Manifold-l] Surfer .GRD import
>
>Are the data in Lat Long?  What units & what
>projection is incoming data and output data?
>
>Does the squishing appear when you project in Manifold to Lat Long?
>
>You´re getting data which is presumably gathered
>at a constant distance interval, that, when
>translated to Lat Long, causes the apparent squishing.
>
>Pat
>
>At 12:37 03-05-2007, M Roseveare wrote:
> >Thanks Pat,
> >
> >The problem occurs though in orthographic projection - long and lat don't
> >come into it unfortunately! The data starts off as orthographic and remains
> >so and hence no distortion should happen. The actual squishing seems to
> >relate to the ratio of the resolutions in the grid. However, changing scale
> >factors etc has no affect.
> >
> >
> >
> >
> >Martin Roseveare
> >Senior Geophysicist
> >
> >
> >Web: www.archaeophysica.co.uk
> >Phone: +44 (0) 1989 730 564
> >Fax: +44 (0) 7050 369 790
> >
> >This e-mail and any attachment may contain proprietary or confidential
> >material and be subject to legal privilege. If you have received it in
>error
> >please promptly erase it from your system and inform the sender.
> >It should not be copied, disclosed to, retained or used in any way by any
> >other party.
> >
> >Nothing in this e-mail should be regarded as representing a binding
>contract
> >unless explicitly stated otherwise. All opinions are those of the sender
>and
> >not necessarily ArchaeoPhysica Ltd.
> >
> >-----Original Message-----
> >From: Pat Waggaman [mailto:waggaman at marimsys.com]
> >Sent: 03 May 2007 17:27
> >To: m.roseveare at archaeophysica.co.uk; manifold-l at directionsmedia.net
> >Subject: Re: [Manifold-l] Surfer .GRD import
> >
> >In bathymetry, back when we were doing a lot of it - we needed the
> >same Surfer to Manifold integration.
> >
> >Our workaround - and this is several Manifold versions ago - was to
> >export CSV from Surfer and then import those tables into Manifold.
> >
> >East - West "squishing will occur with the cos(Lat) x 60 nm of
> >"Longitude compression" as you near the poles.  If that is a problem,
> >raise it as a separate issue, there are questions here of the source
> >data projection and what you want as a finished product.
> >
> >Cheers,
> >
> >Pat
> >
> >
> >
> >At 11:24 03-05-2007, M Roseveare wrote:
> > >Hi all,
> > >
> > >Has anyone come up with a work-around for the Manifold's seemingly dodgy
> > >import of Surfer grids (as surfaces)? I say dodgy because Manifold always
> > >squashes the grid in the east - west direction. I've tried changing
>various
> > >combinations of scale factors but none yield the correct result. It used
>to
> > >be the case that ASCII format grids did this but Surfer 7 binary didn't,
>in
> > >the latest version of Manifold they all come out wrong...
> > >
> > >Any advice welcome - I suspect that it's a bug but wondered whether
>anyone
> > >else has observed the same thing?
> > >
> > >Thanks.
> > >
> > >
> > >
> > >Martin Roseveare
> > >Senior Geophysicist
> > >
> > >
> > >Web: www.archaeophysica.co.uk
> > >Phone: +44 (0) 1989 730 564
> > >Fax: +44 (0) 7050 369 790
> > >
> > >This e-mail and any attachment may contain proprietary or confidential
> > >material and be subject to legal privilege. If you have received it in
> >error
> > >please promptly erase it from your system and inform the sender.
> > >It should not be copied, disclosed to, retained or used in any way by any
> > >other party.
> > >
> > >Nothing in this e-mail should be regarded as representing a binding
> >contract
> > >unless explicitly stated otherwise. All opinions are those of the sender
> >and
> > >not necessarily ArchaeoPhysica Ltd.
> > >
> > >
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