Determine minimum and maximum coordinates and measures
if you decide to specify extent transformations when you create a
spatial reference system.
About this task
Use this process to determine minimum and maximum coordinates
and measures if you:
- Decide to create a new spatial reference system because none
of the spatial reference systems provided with IBM® Spatial Support for Db2 for z/OS® work
with your data.
- Decide to use extent transformations to convert your coordinates.
After you determine the extent values, if any of the coordinates
are decimal values, you need to calculate scale factors. Otherwise,
use the ST_create_srs stored procedure to create a spatial reference
system.
Procedure
To determine the minimum and maximum coordinates and
measures of the locations that you want to represent:
- Determine the minimum and maximum X coordinates.
To
find the minimum X coordinate, identify the X coordinate in your domain
that is furthest west. (If the location lies to the west of the point
of origin, this coordinate will be a negative value.) To find the
maximum X coordinate, identify the X coordinate in your domain that
is furthest east. For example, if you are representing oil wells,
and each one is defined by a pair of X and Y coordinates, the X coordinate
that indicates the location of the oil well that is furthest west
is the minimum X coordinate, and the X coordinate that indicates the
location of the oil well that is furthest east is the maximum X coordinate.
Tip: For multifeature types, such as multipolygons, ensure that
you pick the furthest point on the furthest polygon in the direction
that you are calculating. For example, if you are trying to identify
the minimum X coordinate, identify the westernmost X coordinate of
the polygon that is furthest west in the multipolygon.
- Determine the minimum and maximum Y coordinates.
To
find the minimum Y coordinate, identify the Y coordinate in your domain
that is furthest south. (If the location lies to the south of the
point of origin, this coordinate will be a negative value.) To determine
the maximum Y coordinate, find the Y coordinate in your domain that
is furthest north.
- Determine the minimum and maximum Z coordinates.
The
minimum Z coordinate is the greatest of the depth coordinates and
the maximum Z coordinate is the greatest of the height coordinates.
- Determine the minimum and maximum measures.
If
you are going to include measures in your spatial data, determine
which measure has the highest numerical value and which has the lowest.