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MapCellsReference

Reference raster cells to map coordinates

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Description

A map cells reference object contains information that describes the relationship between a planar map coordinate system and an intrinsic coordinate system that is anchored to the columns and rows of a 2-D spatially referenced raster grid or image of cells.

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. 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.

This image illustrates a 8-by-10 planar raster of cells. The raster cells have an extent of 1 meter in x and y, cover x values in the range [40,50] in meters, and cover y values in the range [20,28] in meters. The boundary of the raster of cells is made up of the outermost boundaries of the outermost cells.

A planar raster of cells. The raster elements appear between grid lines.

To reference a raster of postings to planar map coordinates, use a MapPostingsReference object instead.

Creation

You can use these functions to create MapCellsReference objects:

  • readgeoraster — Import a raster data file as an array and a reference object.

  • maprefcells — Create a map raster reference object by specifying the x and y world limits of the raster and either the size of the raster or the extent of the cells.

  • maprasterref — Convert a world file to a map raster reference object.

  • refmatToMapRasterReference — Convert a referencing matrix to a map raster reference object.

Properties

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Limits of raster in world x-coordinates, specified as a two-element row vector of the form [xMin xMax].

The value of the ProjectedCRS property determines the length units for the raster. This code shows how to find the length units for a raster associated with the map cells reference object R.

R.ProjectedCRS.LengthUnit

Example: [207000 209000]

Data Types: double

Limits of raster in world y-coordinates, specified as a two-element row vector of the form [yMin yMax].

The value of the ProjectedCRS property determines the length units for the raster. This code shows how to find the length units for a raster associated with the map cells reference object R.

R.ProjectedCRS.LengthUnit

Example: [911000 913000]

Data Types: double

Number of rows and columns of the raster or image associated with the referencing object, specified as a two-element vector, [m n], where m represents the number of rows and n the number of columns.

For convenience, you can assign a size vector having more than two elements. This enables assignments like R.RasterSize = size(RGB), where RGB is m-by-n-by-3. In cases like this, the object stores only the first two elements of the size vector and ignores the higher (nonspatial) dimensions.

Example: [200 300]

Data Types: double

This property is read-only.

Geometric nature of the raster, specified as 'cells'. 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 x-coordinate of 1 or m fall within the raster, not on its edges.

Data Types: char

Edge from which column indexing starts, specified as 'south' or 'north'.

Example: 'south'

Data Types: char

Edge from which row indexing starts, specified as 'west' or 'east'.

Example: 'east'

Data Types: char

Extent in world x-coordinates of individual cells, specified as a positive numeric scalar. Distance between the eastern and western limits of a single raster cell. The value is the same for all cells in the raster.

Example: 2.5

Data Types: double

Extent in world y-coordinates of individual cells, specified as a positive numeric scalar. Distance between the northern and southern limits of a single raster cell. The value is the same for all cells in the raster.

Example: 2.5

Data Types: double

This property is read-only.

Extent of the full raster or image as measured in the world system in a direction parallel to its rows, specified as a positive numeric scalar. In the case of a rectilinear geometry, which is most typical, this is the horizontal direction (east-west).

Data Types: double

This property is read-only.

Extent of the full raster or image as measured in the world system in a direction parallel to its columns, specified as a positive numeric scalar. In the case of a rectilinear geometry, which is most typical, this is the vertical direction (north-south).

Data Types: double

This property is read-only.

Raster limits in intrinsic x-coordinates, specified as a two-element row vector of positive integers, [xMin xMax]. For an m-by-n raster, XIntrinsicLimits equals [0.5, m+0.5], because the RasterInterpretation is 'cells'.

Data Types: double

This property is read-only.

Raster limits in intrinsic y-coordinates, specified as a two-element row vector of positive integers, [yMin yMax]. For an m-by-n raster, YIntrinsicLimits equals [0.5, m+0.5], because the RasterInterpretation is 'cells'.

Data Types: double

This property is read-only.

Type of geometric relationship between the intrinsic coordinate system and the world coordinate system, specified as either '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'.

Data Types: char

This property is read-only.

Type of coordinate system to which the image or raster is referenced, specified as 'planar'.

Data Types: char

Projected coordinate reference system (CRS), specified as a projcrs object. A projected CRS consists of a geographic CRS and several parameters that are used to transform coordinates to and from the geographic CRS.

The value of ProjectedCRS determines the length units for the raster. To find the length units, query the LengthUnit property of the projcrs object.

Object Functions

containsDetermine if geographic or map raster contains points
cropToBlockCrop raster reference object to row and column limits of raster
firstCornerXReturn world x-coordinate of map raster index (1,1)
firstCornerYReturn world y-coordinate of map raster index (1,1)
intrinsicToWorld Transform intrinsic to planar world coordinates
sizesMatchDetermine if geographic or map raster object and image or raster are size-compatible
worldFileMatrixReturn world file parameters for transformation
worldGridWorld coordinates of raster elements
worldToDiscrete Transform planar world to discrete coordinates
worldToIntrinsicTransform planar world to intrinsic coordinates

Examples

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Open Live Script

Import a land cover classification of Oahu, Hawaii as an array, a MapCellsReference object, and a colormap by using the readgeoraster function.

[Z,R,cmap] = readgeoraster('oahu_landcover.img');

View the properties of the MapCellsReference object.

R
R = 
  MapCellsReference with properties:

            XWorldLimits: [569857 645907]
            YWorldLimits: [2345284 2405884]
              RasterSize: [2020 2535]
    RasterInterpretation: 'cells'
        ColumnsStartFrom: 'north'
           RowsStartFrom: 'west'
      CellExtentInWorldX: 30
      CellExtentInWorldY: 30
    RasterExtentInWorldX: 76050
    RasterExtentInWorldY: 60600
        XIntrinsicLimits: [0.5 2535.5]
        YIntrinsicLimits: [0.5 2020.5]
      TransformationType: 'rectilinear'
    CoordinateSystemType: 'planar'
            ProjectedCRS: [1x1 projcrs]

Display the land cover classification on a map.

mapshow(Z,cmap,R)

Figure contains an axes object. The axes object contains an object of type image.

More About

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Version History

Introduced in R2013b

See Also

Functions

Objects

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