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# maptrims

Trim regular data grid to latitude-longitude quadrangle

## Syntax

[Z_trimmed] = maptrims(Z,R,latlim,lonlim)
[Z_trimmed] = maptrims(Z,R,latlim,lonlim,cellDensity)
[Z_trimmed, R_trimmed] = maptrims(...)

## Description

[Z_trimmed] = maptrims(Z,R,latlim,lonlim) trims a regular data grid Z to the region specified by latlim and lonlim. By default, the output grid Z_trimmed has the same sample size as the input. 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) and its RasterInterpretation must be 'cells'.

If R is a referencing vector, it must be a 1-by-3 vector 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. latlim and lonlim are two-element vectors, defining the latitude and longitude limits, respectively. The latlim vector has the form:

`[southern_limit northern_limit]`

Likewise, the lonlim vector has the form:

`[western_limit eastern_limit]`

When an individual value in latlim or lonlim corresponds to a parallel or meridian that runs precisely along cell boundaries, the output grid will extend all the way to that limit. But if a limiting parallel or meridian cuts through a column or row of input cells, then the limit will be adjusted inward. In other words, the requested limits will be truncated as necessary to avoid partial cells.

[Z_trimmed] = maptrims(Z,R,latlim,lonlim,cellDensity) uses the scalar cellDensity to reduce the size of the output. If R is a referencing vector, then R(1) must be evenly divisible by cellDensity. If R is a referencing matrix, then the inverse of each element in the first two rows (containing "deltaLat" and "deltaLon") must be evenly divisible by cellDensity.

[Z_trimmed, R_trimmed] = maptrims(...) returns a referencing vector, matrix, or object for the trimmed data grid. If R is a referencing vector, then R_trimmed is a referencing vector. If R is a referencing matrix, then R_trimmed is a referencing matrix. If R is a geographic raster reference object, then R_trimmed is either a geographic raster reference object (when Z_trimmed is non-empty) or [] (when Z_trimmed is empty).

## Examples

```load topo
[subgrid,subrefvec] = maptrims(topo,topolegend,...
[80.25 85.3],[165.2 170.7])

subgrid =
-2826       -2810       -2802       -2793
-2915       -2913       -2905       -2884
-3192       -3186       -3165       -3122
-3399       -3324       -3273       -3214

subrefvec =
1    85   166```

The upper left corner of the grid might differ slightly from that of the requested region. maptrims uses the corner coordinates of the first cell inside the limits.