RE: Thoughts on GALEON Phase 2

• To: "'Wenli Yang'" <yang@xxxxxxxxxxxxxxxxxxxxxxx>, "'GALEON email list'" <galeon@xxxxxxxxxxxxxxxx>
• Subject: RE: Thoughts on GALEON Phase 2
• From: "Clemens Portele" <portele@xxxxxxxxxxxxxxxxxxxxxxxxxx>
• Date: Tue, 28 Feb 2006 12:05:55 +0100

Hi Wenli,

I will try to answer some of your questions based on my understanding, but I
am not an expert on grids, so I hope others will correct me if I am wrong.

1) 3d origin / offset vectors and 2d grid: While the grid itself is two
dimensional, it spans a plane (defines a two-dimensional grid coordinate
system) in a 3d coordinate reference system. Therefore the origin and the
two defining axis vectors have three dimensions.

2) GRID-B: "2." is correct. The origin is the origin of the grid coordinate
system, but not necessarily a corner of the grid. Choosing the origin is
somewhat arbitrary and just a convention - like choosing Greenwich for the
zero meridian. So, my assumption so far was that typically when you specify
a grid for each coverage individually then you would likely end up with a
grid envelope that has (0 0) for the low value, but when you want to use a
common grid system across a series of coverages then this may be different.
By the way, if you have ISO 19123, I think it has additional examples for
rectified grids.

Best regards,
Clemens

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    • From: Wenli Yang