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)

Version History

Introduced before R2006a

expand all

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.