grids.xsd
See ISO/DIS 19136 20.2.
An implicit description of geometry is one in which the items of the geometry do not explicitly appear in the encoding. Instead, a compact notation records a set of parameters, and a set of objects may be generated using a rule with these parameters. This Clause provides grid geometries that are used in the description of gridded coverages and other applications.
In GML two grid structures are defined, namely gml:Grid and gml:RectifiedGrid.
The gml:Grid implicitly defines an unrectified grid, which is a network composed of two or more sets of curves in which the members of each set intersect the members of the other sets in an algorithmic way. The region of interest within the grid is given in terms of its gml:limits, being the grid coordinates of diagonally opposed corners of a rectangular region. gml:axisLabels is provided with a list of labels of the axes of the grid (gml:axisName has been deprecated). gml:dimension specifies the dimension of the grid.
The gml:limits element contains a single gml:GridEnvelope. The gml:low and gml:high property elements of the envelope are each integerLists, which are coordinate tuples, the coordinates being measured as offsets from the origin of the grid along each axis, of the diagonally opposing corners of a "rectangular" region of interest.
A rectified grid is a grid for which there is an affine transformation between the grid coordinates and the coordinates of an external coordinate reference system. It is defined by specifying the position (in some geometric space) of the grid "origin" and of the vectors that specify the post locations.
Note that the grid limits (post indexes) and axis name properties are inherited from gml:GridType and that gml:RectifiedGrid adds a gml:origin property (contains or references a gml:Point) and a set of gml:offsetVector properties.