findm

Latitudes and longitudes of nonzero data grid elements

Syntax

[lat,lon] = findm(Z,R)
[lat,lon] = findm(latz,lonz,Z)
[lat,lon,val] = findm(...)
mat = findm(...)


Description

[lat,lon] = findm(Z,R) computes the latitudes and longitudes of the nonzero elements of a regular data grid, Z. Specify R as a GeographicCellsReference or GeographicPostingsReference object. The RasterSize property of R must be consistent with size(Z).

[lat,lon] = findm(latz,lonz,Z) returns the latitudes and longitudes of the nonzero elements of a geolocated data grid Z, which is an M-by-N logical or numeric array. Typically latz and lonz are M-by-N latitude-longitude arrays, but latz may be a latitude vector of length M and lonz may be a longitude vector of length N.

[lat,lon,val] = findm(...) returns the values of the nonzero elements of Z, in addition to their locations.

mat = findm(...) returns a single output, where mat = [lat lon].

This function works in two modes: with a regular data grid and with a geolocated data grid.

Examples

The data grid can be the result of a logical operation. For example, load elevation raster data and a geographic cells reference object. Then, find all locations with elevations greater than 5500 meters.

load topo60c
[lat,lon] = findm((topo60c > 5500),topo60cR);
[lat lon]

ans =
   34.5000   79.5000
   34.5000   80.5000
   30.5000   84.5000
   28.5000   86.5000

These points are in the Himalayas. Find the grid values at these locations using the geographicToDiscrete and sub2ind functions.

[row,col] = geographicToDiscrete(topo60cR,lat,lon);
indx = sub2ind(size(topo60c),row,col);
heights = topo60c(indx)

heights =
        5559
        5515
        5523
        5731

Version History

Introduced before R2006a

R2024b: findm does not accept referencing vectors or referencing matrices as input

The findm function does not accept referencing vectors or referencing matrices as input. Use a geographic raster reference object, specified as a GeographicCellsReference or GeographicPostingsReference 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.

• Create a geographic reference object for a raster of regularly posted samples by using the georefpostings 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.

R2023b: findm will not accept referencing vectors or referencing matrices as input

When you specify a referencing vector or referencing matrix as input, the findm function issues a warning that it will not accept referencing vectors or referencing matrices as input in a future release.