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

[Markus Neteler]

Benjamin Ducke wrote on 03/06/2007 04:45 PM:
> 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?
> Does this vary between cells? Does GRASS have a function to calculate
> metric lengths between two points in a lat-long system?

In v.to.db we solved that problem some months ago. The function is
Vect_line_geodesic_length() which is found in lib/vector/Vlib/line.c

markus


>  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?
>
> 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
>>>       
>
>