vec2mtx

Convert latitude-longitude vectors to regular data grid

Syntax

[Z,R] = vec2mtx(lat,lon,density)
[Z,R] = vec2mtx(lat,lon,density,latlim,lonlim)
[Z,R] = vec2mtx(lat,lon,Z1,R1)
[Z,R] = vec2mtx(...,'filled')


Description

[Z,R] = vec2mtx(lat,lon,density) creates a regular data grid Z from vector data, placing ones in grid cells intersected by a vector and zeroes elsewhere. R is the raster reference object for the computed grid. lat and lon are vectors of equal length containing geographic locations in units of degrees. density indicates the number of grid cells per unit of latitude and longitude (a value of 10 indicates 10 cells per degree, for example), and must be scalar-valued. Whenever there is space, a buffer of two grid cells is included on each of the four sides of the grid. The buffer is reduced as needed to keep the latitudinal limits within [-90 90] and to keep the difference in longitude limits from exceeding 360 degrees.

[Z,R] = vec2mtx(lat,lon,density,latlim,lonlim) uses the two-element vectors latlim and lonlim to define the latitude and longitude limits of the grid.

[Z,R] = vec2mtx(lat,lon,Z1,R1) uses a pre-existing data grid Z1, georeferenced by R1, to define the limits and density of the output grid. Specify R1 as a GeographicCellsReference object. The RasterSize property of R1 must be consistent with size(Z). With this syntax, the output R is equal to R1.

[Z,R] = vec2mtx(...,'filled'), where lat and lon form one or more closed polygons (with NaN-separators), fills the area outside the polygons with the value two instead of the value zero.

Notes

Empty lat,lon vertex arrays will result in an error unless the grid limits are explicitly provided (via latlim,lonlim or Z1,R1). In the case of explicit limits, Z will be filled entirely with 0s if the 'filled' parameter is omitted, and 2s if it is included.

It's possible to apply vec2mtx to sets of polygons that tile without overlap to cover an area, as in Example 1 below, but using 'filled' with polygons that actually overlap may lead to confusion as to which areas are inside and which are outside.

Examples

Example 1

Convert latitude-longitude polygons to a regular data grid and display as a map.

states = shaperead('usastatelo', 'UseGeoCoords', true);
lat = [states.Lat];
lon = [states.Lon];
[Z,R] = vec2mtx(lat,lon,5,'filled');
figure 
worldmap(Z,R)
geoshow(Z,R,'DisplayType','texturemap')
colormap(flag(3))

Example 2

Combine two separate calls to vec2mtx to create a 4-color raster map showing interior land areas, coastlines, oceans, and world rivers.

load coastlines
[Z,R] = vec2mtx(coastlat,coastlon,1, ...
                [-90 90],[-90 270],'filled');

rivers = shaperead('worldrivers.shp','UseGeoCoords',true);
A = vec2mtx([rivers.Lat],[rivers.Lon],Z,R);
Z(A == 1) = 3;
figure
worldmap(Z,R)
geoshow(Z,R,'DisplayType','texturemap')
colormap([.45 .60 .30; 0 0 0; 0 0.5 1; 0 0 1])

Define Limits and Density of Output Grid Using Spatial Referencing Object

Import US state polygons as a geospatial table. Extract the coordinates of the polygons by converting the geospatial table to a table.

states = readgeotable("usastatelo.shp");
T = geotable2table(states,["Latitude" "Longitude"]);
[lat,lon] = polyjoin(T.Latitude',T.Longitude');

Choose geographic limits.

latlim = [  15  75];
lonlim = [-190 -65];

Specify a grid with 5 cells per degree.

density = 5;

Compute raster size. (M and N both work out to be integers.)

M = density * diff(latlim);
N = density * diff(lonlim);

Create a geographic raster reference object.

R = georasterref("RasterSize", [M N], ...
    "ColumnsStartFrom","north","Latlim",latlim, ...
		"Lonlim",lonlim);

Create a blank grid that is consistent with R in size. vec2mtx requires a data grid as input.

Z = zeros(R.RasterSize);

Overwrite Z with a new grid including state outlines and interiors.

Z = vec2mtx(lat,lon,Z,R,"filled");

Plot the georeferenced grid.

figure; worldmap(Z,R);
geoshow(Z,R,"DisplayType", "texturemap")
colormap(flag(3))

Version History

Introduced before R2006a

R2022b: vec2mtx will not accept referencing vectors or referencing matrices as input

The vec2mtx function will not accept referencing vectors or referencing matrices as input in a future release. Use a geographic raster reference object, specified as a GeographicCellsReference object, as input instead. Reference objects have several advantages over referencing vectors and referencing matrices.

• Unlike referencing vectors and referencing matrices, reference objects have properties that document the size of the associated raster, its geographic limits, and the direction of its rows and columns.

• You can manipulate the limits of geographic rasters associated with reference objects using the geocrop function.

• You can manipulate the size and resolution of geographic rasters associated with reference objects using the georesize function.

To update your code, create a geographic reference object.

• Create a geographic reference object for a raster of cells by using the georefcells function.

• Convert from a referencing vector to a geographic reference object by using the refvecToGeoRasterReference function.

• Convert from a referencing matrix to a geographic reference object by using the refmatToGeoRasterReference function.

Once you have created a reference object, replace uses of the referencing vector or referencing matrix in your code with the reference object.

R2021a: vec2mtx returns reference objects instead of referencing vectors

Starting in R2021a, most syntaxes of the vec2mtx function return a raster reference object instead of a referencing vector. This change is unlikely to affect your existing code because most Mapping Toolbox™ functions that accept referencing vectors as input also accept raster reference objects.

If you specify a referencing vector or matrix as input, then the vec2mtx function still returns a referencing vector or matrix.