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org.opengis.coverage.grid.package-info Maven / Gradle / Ivy

/*
 *    GeoTools - The Open Source Java GIS Toolkit
 *    http://geotools.org
 *
 *    (C) 2011, Open Source Geospatial Foundation (OSGeo)
 *    (C) 2005 Open Geospatial Consortium Inc.
 *
 *    All Rights Reserved. http://www.opengis.org/legal/
 */
/**
 * Quadrilateral grid coverages. The following is adapted from ISO 19123 specification.
 *
 * 
Grid coverages employ a systematic tessellation of the domain. The principal
 * advantage of such tessellations is that they support a sequential enumeration of the elements of
 * the domain, which makes data storage and access more efficient. The tessellation may represent
 * how the data was acquired or how it was computed in a model. The domain of a grid coverage is a
 * set of grid points, including their convex hull in the case of a continuous grid coverage.
 *
 * 
Quadrilateral grid geometry
 *
 * 
A grid 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 a systematic way. The curves are
 * called grid lines; the points at which they intersect are {@linkplain
 * org.opengis.coverage.grid.GridPoint grid points}, and the interstices between the grid lines are
 * {@linkplain org.opengis.coverage.grid.GridCell grid cells}.
 *
 * 
The most common case is the one in which the curves are straight lines, and
 * there is one set of grid lines for each dimension of the grid space. In this case the {@linkplain
 * org.opengis.coverage.grid.GridCell grid cells} are parallelograms or parallelepipeds. In its own
 * coordinate system, such a grid is a network composed of two or more sets of equally spaced
 * parallel lines in which the members of each set intersect the members of the other sets at right
 * angles. It has a set of axes equal in number to the {@linkplain
 * org.opengis.coverage.grid.Grid#getDimension dimension of the grid}. It has one set of grid lines
 * parallel to each axis. The size of the grid is described by a sequence of integers, in which each
 * integer is a count of the number of lines parallel to one of the axes. There are {@linkplain
 * org.opengis.coverage.grid.GridPoint grid points} at all grid line intersections. The axes of the
 * grid provide a basis for defining {@linkplain org.opengis.coverage.grid.GridCoordinates grid
 * coordinates}, which are measured along the axes away from their origin, which is distinguished by
 * having coordinate values of 0. Grid coordinates of grid points are integer numbers. The axes need
 * to be identified to support sequencing rules for associating feature attribute value records to
 * the grid points.
 *
 * 

 *
 * 
NOTE: The dimensions (axes) of a 2-dimensional grid are often called
 * row and column.
 *
 * 
 *
 * 
A grid may be defined in terms of an external {@linkplain
 * org.opengis.referencing.crs.CoordinateReferenceSystem coordinate reference system}. This requires
 * additional information about the location of the grid's origin within the external coordinate
 * reference system, the orientation of the grid axes, and a measure of the spacing between the grid
 * lines. If the spacing is uniform, then there is an affine relationship between the grid and
 * external coordinate system, and the grid is called a rectified grid. If, in addition, the
 * external coordinate reference system is related to the earth by a datum, the grid is a
 * georectified grid. The grid lines of a rectified grid need not meet at right angles; the spacing
 * between the grid lines is constant along each axis, but need not be the same on every axis. The
 * essential point is that the transformation of grid coordinates to coordinates of the external
 * coordinate reference system is an affine transformation.
 *
 * 

 *
 * 
NOTE: The word rectified implies a transformation from an image space
 * to another coordinate reference system. However, grids of this form are often defined initially
 * in an earth-based coordinate system and used as a basis for collecting data from sources other
 * than imagery.
 *
 * 
 *
 * 
A feature attribute value may be of any data type. However, evaluation of a
 * continuous coverage is usually implemented by interpolation methods that can be applied only to
 * numbers or vectors. Other data types are almost always associated with discrete coverages.
 *
 * 
When the relationship between a {@linkplain org.opengis.coverage.grid.Grid
 * grid} and an external {@linkplain org.opengis.referencing.crs.CoordinateReferenceSystem
 * coordinate reference system} is not adequate to specify it in terms of an origin, an orientation,
 * and spacing in that coordinate reference system, it may still be possible to transform the grid
 * coordinates into coordinates in the coordinate reference system. This transformation need not be
 * in analytic form; it may be a table, relating the grid points to coordinates in the external
 * coordinate reference system. Such a grid is classified as a referenceable grid. If the external
 * coordinate reference system is related to the earth by a datum, the grid is a georeferenceable
 * grid. A referenceable grid is associated with information that allows the location of all points
 * in the grid to be determined in the coordinate reference system, but the location of the points
 * is not directly available from the grid coordinates, as opposed to a rectified grid where the
 * location of the points in the coordinate reference system is derivable from the properties of the
 * grid itself. The transformation produced by the information associated with a referenceable grid
 * will produce a grid as seen in the coordinate reference system, but the grid lines of that grid
 * need not be straight or orthogonal, and the grid cells may be of different shapes and sizes.
 *
 * 
Cell structures
 *
 * 
The term "grid cell" refers to two concepts: one important from the
 * perspective of data collection and portrayal, the other important from the perspective of grid
 * coverage evaluation. The ambiguity of this term is a common cause of positioning error in
 * evaluating or portraying grid coverages.
 *
 * 
The feature attribute values associated with a {@linkplain
 * org.opengis.coverage.grid.GridPoint grid point} represent characteristics of the real world
 * measured or observed within a small space surrounding a sample point represented by the grid
 * point. The grid lines connecting these points form a set of {@linkplain
 * org.opengis.coverage.grid.GridCell grid cells}. A common simplifying assumption is that the
 * sample space is equally divided among the sample points, so that the sample spaces are
 * represented by a second set of cells congruent to the first but offset so that each has a grid
 * point at its centre. Evaluation of a grid coverage is based on interpolation between grid points,
 * i.e., within a grid cell bounded by the grid lines that connect the grid points that represent
 * the sample points.
 *
 * 
In the ISO 19123 International Standard, the term grid cell
 * refers to the cell bounded by the grid lines that connect the grid points. The term sample
 * space refers to the observed or measured space surrounding a sample point. The term
 * footprint refers to a representation of a sample space in the context of some
 * coordinate reference system.
 *
 * 
In dealing with gridded data, e.g., for processing or portrayal, it is often
 * assumed that the size and shape of the sample spaces are a simple function of the spatial
 * distribution of the sample points, and typically that the grid cells and the sample cells are
 * congruent.
 *
 * 
In fact, the size and shape of the sample space are determined by the method
 * used to measure or calculate the attribute value. In the simplest case, the sample space is the
 * sample point. It is often a disc, a sphere, or a hypersphere surrounding the sample point. In the
 * case of sensed data the size and shape of the sample space is also a function of the sensor model
 * and its position relative to the sample point, and may be quite complex. Adjacent sample spaces
 * may be coterminous or they may overlap or underlap.
 *
 * 
In addition to affecting the size and shape of the sample space, the
 * measurement technique affects the applicability of the observed or measured value to the sample
 * space. It is often assumed that the recorded value represents the mean value for the sample
 * space. In fact, elements of the sample space may not contribute uniformly to the result, so that
 * it is better conceived as a weighted average where the weighting is a function of position within
 * the sample space. Interpolation methods may be designed specifically to deal with characteristics
 * of the sample space.
 *
 * 
Transformation (e.g., rectification) between grid coordinates and an external
 * coordinate reference system may distort the representation of the sample space in a way that
 * causes interpolation errors.
 *
 * @version ISO 19123:2004
 * @since GeoAPI 2.0
 */
package org.opengis.coverage.grid;