Fwd: Re: [GRASS-dev] VTK export for lat-long locations

["Sören Gebbert"]

Hi Benjamin,
-------- Original-Nachricht --------
Datum: Tue, 06 Mar 2007 16:45:14 +0100
Von: Benjamin Ducke <benjamin.ducke at ufg.uni-kiel.de>
An: 
CC: grass-dev at grass.itc.it
Betreff: Re: Fwd: Re: [GRASS-dev] VTK export for lat-long locations

> Wow, that explains the result I got!
> So I guess you need to know exactly how many meters a lat/long cell
> dimension is in the current projection, so you can scale the Z axis
> accordingly?

Yes, thats the point. And i need to know where to start.

> Does this vary between cells? Does GRASS have a function to calculate

It changes with every raster row.

> metric lengths between two points in a lat-long system? If so, I guess
> you would need to take the the metric distance between corner points of
> a lat-long cell and use the value for Z axis scaling?

AFAIK these functions are implemented in grass (lib/gis/area* and stuff).

The point is, im not very familiar with this kind of coordinate transformation, and even if i know the distance between each point,
i dont know where to start with 0,0 in metric coordiantes. :/

Maybe im a bit dumb?

Best regards
Soeren

> 
> Sören Gebbert wrote:
> > -------- Original-Nachricht --------
> > Datum: Tue, 06 Mar 2007 16:06:18 +0100
> > Von: "Sören Gebbert" <soerengebbert at gmx.de>
> > An: Benjamin Ducke <benjamin.ducke at ufg.uni-kiel.de>
> > CC: 
> > Betreff: Re: [GRASS-dev] VTK export for lat-long locations
> > 
> > Hi Benjamin,
> > please dont use the vtk export modules with lat/lon projections.
> > The vtk export modules in grass are not 
> > usable with lat/lon projections right now.
> > I think i should put this info to the html docs.
> > 
> > The lat/lon coordiantes are used to define the coordinates for each
> point.
> > VTK interpret these coordinates as planimetric and not as lat/lon.
> > This is not that bad for x,y coordinates, but for the height (z
> coordinate).
> > Because if x and y lat/lon coordiantes are of type [54.001/34.002] and
> the
> > height varies from 0m - 500m you will get a senseless result.
> > 
> > I still dont know exactly how to implement a meaningful 
> > lat/lon ->planimetric coordinate transformation to get rid 
> > fo this behaviour.
> > 
> > Any suggestions are welcome.
> > 
> > Best regards
> > Soeren
> > 
> > 
> > -------- Original-Nachricht --------
> > Datum: Tue, 06 Mar 2007 15:57:17 +0100
> > Von: Benjamin Ducke <benjamin.ducke at ufg.uni-kiel.de>
> > An: GRASS devel <grass-dev at grass.itc.it>
> > CC: 
> > Betreff: [GRASS-dev] VTK export for lat-long locations
> > 
> >> Hi everyone,
> >>
> >> I just tested r.out.vtk in a lat-long location and all I got when I
> >> loaded the VTK file in Paraview (2.6.0), was a single line of data
> >> projecting through the origin of the coordinate system.
> >>
> >> Does anyone have any experiences with VTK/Paraview and lat-long data?
> >>
> >> Thanks,
> >>
> >> Benjamin
> >>
> >>
> >> -- 
> >> Benjamin Ducke, M.A.
> >> Archäoinformatik
> >> (Archaeoinformation Science)
> >> Institut für Ur- und Frühgeschichte
> >> (Inst. of Prehistoric and Historic Archaeology)
> >> Christian-Albrechts-Universität zu Kiel
> >> Johanna-Mestorf-Straße 2-6
> >> D 24098 Kiel
> >> Germany
> >>
> >> Tel.: ++49 (0)431 880-3378 / -3379
> >> Fax : ++49 (0)431 880-7300
> >> www.uni-kiel.de/ufg
> >>
> >> _______________________________________________
> >> grass-dev mailing list
> >> grass-dev at grass.itc.it
> >> http://grass.itc.it/mailman/listinfo/grass-dev
> > 
> 
> -- 
> Benjamin Ducke, M.A.
> Archäoinformatik
> (Archaeoinformation Science)
> Institut für Ur- und Frühgeschichte
> (Inst. of Prehistoric and Historic Archaeology)
> Christian-Albrechts-Universität zu Kiel
> Johanna-Mestorf-Straße 2-6
> D 24098 Kiel
> Germany
> 
> Tel.: ++49 (0)431 880-3378 / -3379
> Fax : ++49 (0)431 880-7300
> www.uni-kiel.de/ufg
> 
> _______________________________________________
> grass-dev mailing list
> grass-dev at grass.itc.it
> http://grass.itc.it/mailman/listinfo/grass-dev

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