spatial types: looking ahead to spatial search
DESCRIPTION
It is not enough to collect the data and produce data products. In order to be useful the data has to be used. To facilitate data use eventually a search interface has to be developed, probably many. And those interfaces can only be as good as the metadata they have to work with. HDF is not so much a data format as a file format that packages the data with the metadata, so facilitating data access by providing adequate and appropriate metadata starts with data production. In many areas this is not much of a challenge. The temporal coverage of the granules is generally well known, channel and derived parameter names are generally just a matter of convention, etc. But spatial coverage can vary quite a bit, especially for remotely sensed data, and can often be problematic. This paper goes through the five most common spatial types (point, grid, tile, scene, and swath) discusses the problems associated with each, and makes some recommendations for the metadata that needs to be included with the data to facilitate fast, efficient, accurate search when the time comes.TRANSCRIPT
Fall, 2004 National Snow and Ice Data Center 1
Spatial Types
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Point Data
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Sparse Point Data
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Dense Point Data
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Gridded Data
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MODIS CMG - Coverage
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SSM/I Ease-grid
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SSM/I EASE Grid - Coverage
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Polar Stereo (Sea Ice)
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Polar Stereo (Sea Ice) - Coverage
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Polar Stereo (Sea Ice) - Coverage
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Polar Stereo (Sea Ice) - Coverage
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Polar Stereo (Sea Ice) - Coverage
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Polar Stereo (Sea Ice) - Coverage
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Polar Stereo (Sea Ice) - Coverage
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Tiles
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05v08h Coverage
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05v08h w/ lat/lon bounding box
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05v08h Spherical
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AVHRR L1b (Scene)
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AVHRR L1b (Scene) - Coverage
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AVHRR L1b (Scene) - Coverage
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AVHRR L1b (Scene) - Coverage
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AVHRR L1b (Scene) - Coverage
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AVHRR L1b (Scene) - Coverage
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Weird Shape
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Full Orbit - Coverage
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Full Orbit - LLBox
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Full Orbit – Lat/lon Blocks
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Full Orbit – Spherical Blocks
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Full Orbit - Coverage
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Full Orbit - Coverage
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Full Orbit – Using Backtrack
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Summary
Point Data: use points or multi-points.
Grids: Use a lat/lon bounding box if appropriate, otherwise use a spherical n-gon. Accuracy is more important than speed.
Tiled Data: A form of regional grid, use a lookup table.
Scenes: Use a spherical quadrilateral, maybe up to a spherical decagon for larger scenes. Speed is more important than accuracy.
Orbits: The best way to define the coverage of an orbit is to define the orbit. The best way to search for orbital data is to search orbits. Use Backtrack.