# Documentation

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# geointerp

Geographic raster interpolation

## Syntax

``Vq = geointerp(V,R,latq,lonq)``
``Vq = geointerp(___,method)``

## Description

example

````Vq = geointerp(V,R,latq,lonq)` interpolates the geographically referenced raster `V`, using bilinear interpolation. The function returns a value in `Vq` for each of the query points in arrays `latq` and `lonq`. `R` is a geographic raster reference object that specifies the location and extent of data in `V`.```
````Vq = geointerp(___,method)` specifies alternate interpolation methods.```

## Examples

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`load topo`

Create a raster reference object associated with the `topo` raster grid.

`R = georefcells(topolatlim,topolonlim,size(topo))`
```R = GeographicCellsReference with properties: LatitudeLimits: [-90 90] LongitudeLimits: [0 360] RasterSize: [180 360] RasterInterpretation: 'cells' ColumnsStartFrom: 'south' RowsStartFrom: 'west' CellExtentInLatitude: 1 CellExtentInLongitude: 1 RasterExtentInLatitude: 180 RasterExtentInLongitude: 360 XIntrinsicLimits: [0.5 360.5] YIntrinsicLimits: [0.5 180.5] CoordinateSystemType: 'geographic' AngleUnit: 'degree' ```

Define the points you want to interpolate using latitude and longitude.

```mylats = [-40 -20 20 40]; mylons = [ 42 54 38 62];```

Interpolate the values at the defined points.

`Vinterpolated = geointerp(topo,R,mylats,mylons)`
```Vinterpolated = 1.0e+03 * -2.8327 -4.3855 -0.7125 0.1700 ```

## Input Arguments

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Georeferenced raster grid, specified as numeric or logical array.

Data Types: `single` | `double` | `int8` | `int16` | `int32` | `int64` | `uint8` | `uint16` | `uint32` | `uint64` | `logical`

Geographic raster, specified as a `GeographicCellsReference` or `GeographicPostingsReference` object.

To convert a referencing matrix to a geographic raster reference object, use `refmatToGeoRasterReference`.To convert a referencing vector to a geographic raster reference object, use `refvecToGeoRasterReference`.

Latitude of query point coordinates, specified as a numeric array.

Data Types: `single` | `double`

Longitude of query point coordinates, specified as a numeric array.

Data Types: `single` | `double`

Interpolation methods, specified as one of these character vectors or strings.

MethodDescription
`'nearest'`Nearest neighbor interpolation
`'linear'`Bilinear interpolation
`'cubic'`Bicubic interpolation
`'spline'`Spline interpolation

Data Types: `char` | `string`

## Output Arguments

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Interpolated values, returned as a numeric array.