Changes between Version 1 and Version 2 of MultipleProjectionsJohn


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Timestamp:
12/23/06 12:25:56 (13 years ago)
Author:
jonathan
Comment:

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  • MultipleProjectionsJohn

    v1 v2  
    11I prefer this proposal, because it represents each coordinate system explicitly as something that can be referred to by name.  That makes it possible for a coordinate system to be represented even if there is no variable that uses it (yet).  Disadvantages include the length of the representation and the arbitrariness of the type chosen to represent the coordinate system variables {{{Dutch_CoordSystem}}} and {{{German_CoordSystem}}}.  These variables only exist to hang attributes on, so both their type and value are irrelevant. Nevertheless, this representation seems to capture the intent cleanly, and the extra name required for the coordinate system provides an additional opportunity for making the coordinate systems clear.
    22-- Russ
     3
     4This proposal introduces a coordinate system variable which is
     5separate from the data variable. The coordinate system variable points to the
     6grid mapping and the projection coordinates. The data variable points to one or
     7more coordinate system variables. The advantage of this is that it directly
     8associates the grid mapping and the projection coordinates, and it saves having
     9to make the same association on every data variable. I would say that this is
     10an attractive idea, and it is quite natural to introduce this abstraction as a
     11way of interpreting the file. However, I think it would be inconsistent to
     12separate the coordinate system from the data variable *only* in this rather
     13specialised case, while we do not do it in the commoner situations where the
     14coordinate system is defined by the 1D coordinate variables, or by 2D lat-lon
     15auxiliary coordinate variables. Also, this abstraction may make the file harder
     16to understand and to use by simple programs or inexpert users. Users are
     17accustomed to seeing the coordinates attached to the data variable, which seems
     18an obvious approach. ''Jonathan''