# minvtran

Unproject features from map to geographic coordinates

## Syntax

```[lat,lon] = minvtran(x,y) [lat,lon,alt] = minvtran(x,y,z) [...] = minvtran(mstruct,...) ```

## Description

`[lat,lon] = minvtran(x,y)` applies the inverse transformation defined by the map projection in the current map axes. Using `minvtran`, you can convert point locations and line and polygon vertices in a planar, projected map coordinate system to latitudes and longitudes.

`[lat,lon,alt] = minvtran(x,y,z)` applies the inverse projection to 3-D input, resulting in 3-D output. If the input `Z` is empty or omitted, then ```Z = 0``` is assumed.

`[...] = minvtran(mstruct,...)` takes a valid map projection structure as the first argument. In this case, no map axes is needed.

## Examples

Before using any transformation functions, it is necessary to create a map projection structure. You can do this with `axesm` or the `defaultm` function:

```mstruct = defaultm('mercator'); mstruct.origin = [38.89 -77.04 0]; mstruct = defaultm(mstruct);```

The following latitude and longitude data for the District of Columbia is obtained from the `usastatelo` shapefile:

```dc = shaperead('usastatelo', 'UseGeoCoords', true,... 'Selector',{@(name) strcmpi(name,'District of Columbia'),... 'Name'}); lat = [dc.Lat]'; lon = [dc.Lon]'; [lat lon] ans = 38.9000 -77.0700 38.9500 -77.1200 39.0000 -77.0300 38.9000 -76.9000 38.7800 -77.0300 38.8000 -77.0200 38.8700 -77.0200 38.9000 -77.0700 38.9000 -77.0500 38.9000 -77.0700 NaN NaN```

This data can be projected into Cartesian coordinates of the Mercator projection using the `mfwdtran` function:

```[x,y] = mfwdtran(mstruct,lat,lon); [x y] ans = -0.0004 0.0002 -0.0011 0.0010 0.0001 0.0019 0.0019 0.0002 0.0001 -0.0019 0.0003 -0.0016 0.0003 -0.0003 -0.0004 0.0002 -0.0001 0.0002 -0.0004 0.0002 NaN NaN```

To transform the projected x-y data back into the unprojected geographic system, use the `minvtran` function:

```[lat2,lon2] = minvtran(mstruct,x,y); [lat2 lon2] ans = 38.9000 -77.0700 38.9500 -77.1200 39.0000 -77.0300 38.9000 -76.9000 38.7800 -77.0300 38.8000 -77.0200 38.8700 -77.0200 38.9000 -77.0700 38.9000 -77.0500 38.9000 -77.0700 NaN NaN``` 