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Accessing 2D Matrix-Organized Tiled Datasets

Original Post by: Shash Thu Aug 6 19:47:55 2009


I am evaluating the CDB API, and trying to access some tiled datasets, namely Elevation datasets.

My question is regarding locating corner data elements, as described in the CDB Specification, version 3.0 - October 2008, page 5-14. Regarding equation 5-1, how are TileLatitude and TileLongitude computed, given a particular lat/lng? Looking at the latitude calculation in eq. 5-1, it is obvious that the TileLatitude must be a higher magnitude than the data element latitude, or the indices become negative.

GeoCells are referenced with the South West corner (bottom, left). Question is how are Tiles referenced, by the SW corner or the NW corner? For example, if I need to access data element at lng=N25, and E55, then the GeoCell location is [N25, E55], there is only 1 tile in that GeoCell at LOD 0, what should the data element indices be?

If I have missed any discussion in the spec regarding TileLatitude/TileLongitude, I'd appreciate a pointer to that as well.

Thanks in advance for the help!


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Original Post by: Shash Thu Aug 6 20:00:06 2009

I should have mentioned, for further clarification, that this question is related to Figure 5-2 Corner Grid Data Elements, Page 5-13. It seems to indicate that Data Element indices are referenced from the NW corner.

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