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meshgrat

Construct map graticule for surface object display

Syntax

[lat, lon] = meshgrat(Z, R)
[lat, lon] = meshgrat(Z, R, gratsize)
[lat, lon] = meshgrat(lat, lon)
[lat, lon] = meshgrat(latlim, lonlim, gratsize)
[lat, lon] = meshgrat(lat, lon, angleunits)
[lat, lon] = meshgrat(latlim, lonlim, angleunits)
[lat, lon] = meshgrat(latlim, lonlim, gratsize, angleunits)

Description

[lat, lon] = meshgrat(Z, R) constructs a graticule for use in displaying a regular data grid, Z. In typical usage, a latitude-longitude graticule is projected, and the grid is warped to the graticule using MATLAB® graphics functions. In this two-argument calling form, the graticule size is equal to the size of Z. R can be a geographic raster reference object, a referencing vector, or a referencing matrix.

If R is a geographic raster reference object, its RasterSize property must be consistent with size(Z).

If R is a referencing vector, it must be 1-by-3 with elements:

[cells/degree northern_latitude_limit western_longitude_limit]

If R is a referencing matrix, it must be 3-by-2 and transform raster row and column indices to/from geographic coordinates according to:

[lon lat] = [row col 1] * R

If R is a referencing matrix, it must define a (non-rotational, non-skewed) relationship in which each column of the data grid falls along a meridian and each row falls along a parallel.

[lat, lon] = meshgrat(Z, R, gratsize) produces a graticule of size gratsize. gratsize is a two-element vector of the form [number_of_parallels number_of_meridians]. If gratsize = [], then the graticule returned has the default size 50-by-100. (But if gratsize is omitted, a graticule of the same size as Z is returned.) A finer graticule uses larger arrays and takes more memory and time but produces a higher fidelity map.

[lat, lon] = meshgrat(lat, lon) takes the vectors lat and lon and returns graticule arrays of size numel(lat)-by-numel(lon). In this form, meshgrat is similar to the MATLAB function meshgrid.

[lat, lon] = meshgrat(latlim, lonlim, gratsize) returns a graticule mesh of size gratsize that covers the geographic limits defined by the two-element vectors latlim and lonlim.

[lat, lon] = meshgrat(lat, lon, angleunits), [lat, lon] = meshgrat(latlim, lonlim, angleunits), and [lat, lon] = meshgrat(latlim, lonlim, gratsize, angleunits) use the string angleunits to specify the angle units of the inputs and outputs. The string angleunits can be either 'degrees' (the default) or 'radians'.

The graticule mesh is a grid of points that are projected on a map axes and to which surface map objects are warped. The fineness, or resolution, of this grid determines the quality of the projection and the speed of plotting. There is no hard and fast rule for sufficient graticule resolution, but in general, cylindrical projections need very few graticules in the longitudinal direction, while complex curve-generating projections require more.

Examples

Make a (coarse) graticule for the entire world:

latlim = [-90 90]; 
lonlim = [-180 180];
[lat,lon] = meshgrat(latlim,lonlim,[3 6])

lat =
  -90.0000  -90.0000  -90.0000  -90.0000  -90.0000  -90.0000
         0         0         0         0         0         0
   90.0000   90.0000   90.0000   90.0000   90.0000   90.0000
lon =
 -180.0000 -108.0000  -36.0000   36.0000  108.0000  180.0000
 -180.0000 -108.0000  -36.0000   36.0000  108.0000  180.0000
 -180.0000 -108.0000  -36.0000   36.0000  108.0000  180.0000

These paired coordinates are the graticule vertices, which are projected according to the requirements of the desired map projection. Then a surface object like the topo map can be warped to the grid.

See Also

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