A map raster reference object encapsulates the relationship
between a planar map coordinate system and a system of intrinsic coordinates
anchored to the columns and rows of a 2-D spatially referenced raster
grid or image. See Intrinsic Coordinate System.
Typically, the raster is sampled regularly in the planar world x and
world y coordinates of the map system, such that
the intrinsic x and world x axes
align and the intrinsic y and world y axes
align. When this is true, the relationship between the two systems
is rectilinear.
More generally, and much more rarely, their relationship is
affine. The affine relationship allows for a possible rotation (and
skew).
In either case, rectilinear or affine, the sample spacing from
row to row need not equal the sample spacing from column to column.
If the raster data set is interpreted as comprising a grid of cells
or pixels, the cells or pixels need not be square. In the most general
case, they could conceivably be parallelograms, but in practice they
are always rectangular.
Construction
You can use either of the following functions to construct a
map raster reference object:
By default, maprasterref creates a map raster
reference object with the raster interpretation of cells (map.rasterref.MapCellsReference).
To create a map raster reference object with a raster interpretation
of postings (map.rasterref.MapPostingsReference),
call maprasterref specifying the rasterInterpretation input
argument.
For example, this syntax constructs a MapRasterReference object
with default property settings:
Two-element vector [M N] specifying the number
of rows (M) and columns (N)
of the raster or image associated with the referencing object. For
convenience, you can assign a size vector having more than two elements
to RasterSize. This enables assignments like R.RasterSize
= size(RGB), where RGB is M-by-N-by-3.
In cases like this, only the first two elements of the size vector
are stored. Higher (non-spatial) dimensions are ignored. M and N must
be positive in all cases and must be 2 or greater when RasterInterpretation is 'postings'.
Default: [2 2]
RasterInterpretation
Defines the geometric nature of the raster and controls the
handling of raster edges, among other things.
The value 'cells' indicates that the raster
comprises a grid of quadrangular cells, and is bounded on all sides
by cell edges. For an M-by-N raster,
points with an intrinsic X-coordinate of 1 or N or
an intrinsic Y-coordinate of 1 or M fall
within the raster, not on its edges.
The value 'postings' indicates that the raster
comprises a grid of sample points, where rows or columns of samples
run along the edge of the grid. For an M-by-N raster,
points with an intrinsic X-coordinate of 1 or N and/or
an intrinsic Y-coordinate of 1 or M fall
right on an edge (or corner) of the raster.
Cannot be set.
Default: 'cells'
ColumnsStartFrom
Edge where column indexing starts. A string that equals 'south' or 'north'.
Default: 'south'
RowsStartFrom
Edge from which row indexing starts. A string that equals 'west' or 'east'.
Default: 'west'
CellExtentInWorldX
Supported by map.rasterref.MapCellsReference.
Extent in world X of individual cells. Distance
between the eastern and western limits of a single raster cell. The
value is always positive, and is the same for all cells in the raster.
Cannot be set.
CellExtentInWorldY
Supported by map.rasterref.MapCellsReference.
Extent in world Y of individual cells. Distance
between the northern and southern limits of a single raster cell.
The value is always positive, and is the same for all cells in the
raster.
Cannot be set.
SampleSpacingInWorldX
Supported by map.rasterref.MapPostingsReference.
Extent in world X of individual cells. Distance
between the eastern and western limits of a single raster cell. The
value is always positive, and is the same for all cells in the raster.
Cannot be set.
SampleSpacingInWorldY
Supported by map.rasterref.MapPostingsReference.
Extent in world Y of individual cells. Distance
between the northern and southern limits of a single raster cell.
The value is always positive, and is the same for all cells in the
raster.
Cannot be set.
RasterExtentInWorldX
Extent of the full raster or image as measured in the world
system in a direction parallel to its rows. In the case of a rectilinear
geometry, which is most typical, this is the horizontal direction
(east-west).
Cannot be set.
RasterExtentInWorldY
Extent of the full raster or image as measured in the world
system in a direction parallel to its columns. In the case of a rectilinear
geometry, which is most typical, this is the vertical direction (north-south).
Cannot be set.
XIntrinsicLimits
Raster limits in intrinsic x.
Two-element row vector of the form [xMin xMax].
For an M-by-N raster with RasterInterpretation equal
to 'postings', it equals [1 N].
For 'cells', it equals [0.5, N + 0.5].
Cannot be set.
YIntrinsicLimits
Raster limits in intrinsic y
Two-element row vector of the form [yMin yMax].
For an M-by-N raster with RasterInterpretation equal
to 'postings', it equals [1 M].
For 'cells', it equals [0.5, M + 0.5].
Cannot be set.
TransformationType
Type of geometric relationship between the intrinsic coordinate
system and the world coordinate system. The string has the value 'rectilinear' or 'affine'.
Its value is 'rectilinear' when world x depends
only on intrinsic x and vice versa, and world y depends
only on intrinsic y and vice versa. When the value
is 'rectilinear', the image displays without rotation
in the world system, although it might be flipped. Otherwise, the
value is 'affine'.
Cannot be set.
CoordinateSystemType
Type of coordinate system to which the image or raster is referenced.
It is a constant string with value 'planar'.
A 2-D Cartesian system with its x-axis running
parallel to the rows of a raster or image and its y-axis
running parallel to the columns. x increases by
1 from column to column, and y increases by 1 from
row to row.
The Mapping Toolbox™ and Image Processing Toolbox™ use
the convention for the location of the origin relative to the raster
cells or sampling points such that, at a sample location or at the
center of a cell, x has an integer value equal
to the column index. Likewise, at a sample location or at the center
of a cell, y has an integer value equal to the
row index. For details, see Image Coordinate Systems in
the Image Processing Toolbox documentation.