Thanks for the information, i had already found some things like that. <br>As a matter of fact it appears i misunderstood what i need to do. <br>I need to reproject data in that are on "some kind" of sinusoidal projection with a GEM6 ellispsoid to some regular lat/lon grid. <br>
<br>My initial raster in "GEM6" is georeferenced (gcps) so i think i will be able to use gdal to reproject this data. As i can't test this because i do not have any input data right now, can anyone confirm ?<br>
<br><div class="gmail_quote">2009/5/6 Peter J Halls <span dir="ltr"><<a href="mailto:P.Halls@york.ac.uk">P.Halls@york.ac.uk</a>></span><br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
For detailed information on DGG's see <a href="http://cs.sou.edu/%7Esahrk/dgg/" target="_blank">http://cs.sou.edu/~sahrk/dgg/</a>.<br>
<br>
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.<br>
<br>
'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.'<br>
<br>
I rather doubt GDAL has the functions for this approach, but I may be wrong.<br>
<br>
Peter<br>
<br>
reg ister wrote:<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><div><div></div><div class="h5">
Hello everyone,<br>
i ve ran into some odd projection and i would like to know if i can use gdal<br>
to reproject georeferenced data in this projection (gcp included in my<br>
raster) . I'm used to gdal and projections but here i can't seem to find<br>
enough information.<br>
The idea is to reproject to a DGG (discrete global grid) The projection is<br>
an adapted sinusoidal grid with an ellipsoid based on GEM 6 model (Goddard<br>
Earth Model)<br>
<br>
Any insight or experience is apreciated but if no one already encountered<br>
such a thing here are some precise questions that can help me<br>
<br>
I never encountered the name DGG before, does it implies some specific<br>
feature about projection or is it just a synonym of grid ?<br>
the grid considered seems to be composed of octaedrons, is it even relevant<br>
when projecting data considering i have the ellipsoid and type of projection<br>
?<br>
I have the major and minor axises for GEM 6 ellipsoid, would it be correct (<br>
and possible ) to specify these to gdal along with a sinusoidal projection<br>
to reproject my data?<br>
as you may have noticed, is said adapted sinusoidal grid... i don't what<br>
adapted implies. would it be possible in gdal to "adapt" the built in<br>
sinusoidal projection ( to what cost in dev )?<br>
<br>
<br>
any help apreciated.<br>
<br>
Thanks everyone, keep up the good work<br>
<br>
<br>
<br></div></div>
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Peter J Halls, GIS Advisor, University of York<br>
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