[gdal-dev] GEM 6 sinusoidal projection

[Peter J Halls]

For detailed information on DGG's see http://cs.sou.edu/~sahrk/dgg/.

There is a paper in the journal Cartography and Geographic Information Science, 
'Geodesic Discrete Global Grid Systems' by Kevin Sahr, Denis White and A. Jon 
Kimerling, linked from the above web page, which surveys DDG in detail.  In 
summary, DDG is a data structure, based on 'regular, multi-resolution partitions 
of polyhedra' where 'each region has a single point associated with it'.  It is 
analogous to Voronoi cells, but regular, rather than irregular.  'Usually, this 
series consists of increasingly finer resolution grids; i.e., the grids in the 
series have a monotonically increasing number of cells.' - this seems similar to 
using a quad-tree approach.

'Grids based on square partitions are by far the most familiar to users, and 
they map efficiently to common data structures and display devices. But such 
grids also have limitations. Discrete Global Grid Systems induced by the 
latitude–longitude graticule do not have equal-area cell regions, which 
complicates statistical analysis on these grids.'  A wide variety of cell forms 
have been proposed by various workers but, according to Sahr et al, 'It is 
highly unlikely that any single Geodesic DGGS will ever prove optimal for all 
applications. Many of the proposed systems include design innovations in 
particular areas, though their construction may have involved other, less 
desirable design choices.'

I rather doubt GDAL has the functions for this approach, but I may be wrong.

Peter

reg ister wrote:
> Hello everyone,
> i ve ran into some odd projection and i would like to know if i can use gdal
> to reproject georeferenced data in this projection (gcp included in my
> raster) . I'm used to gdal and projections but here i can't seem to find
> enough information.
> The idea is to reproject to a DGG (discrete global grid) The projection is
> an adapted sinusoidal grid with an ellipsoid based on GEM 6 model (Goddard
> Earth Model)
> 
> Any insight or experience is apreciated but if no one already encountered
> such a thing here are some precise questions that can help me
> 
> I never encountered the name DGG before, does it implies some specific
> feature about projection or is it just a synonym of grid ?
> the grid considered seems to be composed of octaedrons, is it even relevant
> when projecting data considering i have the ellipsoid and type of projection
> ?
> I have the major and minor axises for GEM 6 ellipsoid, would it be correct (
> and possible ) to specify these to gdal along with a sinusoidal projection
> to reproject my data?
> as you may have noticed, is said adapted sinusoidal grid... i don't what
> adapted implies. would it be possible in gdal to "adapt" the built in
> sinusoidal projection ( to what cost in dev )?
> 
> 
> any help apreciated.
> 
> Thanks everyone, keep up the good work
> 
> 
> 
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-- 
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Peter J Halls, GIS Advisor, University of York
Telephone: 01904 433806     Fax: 01904 433740
Snail mail: Computing Service, University of York, Heslington, York YO10 5DD
This message has the status of a private and personal communication
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