Mapping Toolbox

mfwdtran

Transform unprojected Greenwich data to a projected Cartesian coordinate system

Syntax

• [x,y] = mfwdtran(lat,lon)
  [x,y,z] = mfwdtran(lat,lon,alt)
  [x,y,z,struct] = mfwdtran(lat,lon,alt,object)
  [...] = mfwdtran(mstruct,...)
  

Description

[x,y] = mfwdtran(lat,lon) transforms unprojected Greenwich data to the projected Cartesian coordinate frame using the map projection defined for the current axes. No clipping or trimming of data is performed with this calling form.

[x,y,z] = mfwdtran(lat,lon,alt) transforms the three-dimensional data to the projected Cartesian coordinate frame using the map projection defined for the current axes. If alt = [] or alt is omitted, the default alt = 0 is used.

[x,y,z,struct] = mfwdtran(lat,lon,alt,object) clips and trims the data during the transformation process. Allowable object strings are 'surface', 'line', 'patch', 'light', 'text', and 'none'. 'none' will result in no clipping or trimming of the input data. The output struct is a structure containing information about the clips and trims associated with the transformed object. This structure is also found in the displayed object's UserData property.

[...] = mfwdtran(mstruct,...) requires a valid map projection structure as the first argument. This structure is used to define the map projection calculations performed. No map axes need be displayed when using this
calling form.

Examples

The following latitude and longitude data for the District of Columbia is obtained from the usalo workspace:

• load usalo
  lat = state(51).lat;
  lon = state(51).long;
  [lat lon]
  ans =
     38.9000  -77.0700
     38.9000  -77.0500
     38.9000  -77.0700
     38.8700  -77.0200
     38.8000  -77.0200
     38.7800  -77.0300
     38.9000  -76.9000
     39.0000  -77.0300
     38.9500  -77.1200
     38.9000  -77.0700
  

Before projecting the data, it is necessary to define projection parameters. This can be done with the axesm command, or with the defaultm command:

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

Now that the projection parameters have been set, transform the District of Columbia data into the Cartesian frame using the Mercator projection:

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

See Also

defaultm	Initialize a default map data structure
gcm	Get current map data structure
minvtran	Map inverse transformation
vfwdtran	Vector forward transformation
vinvtran	Vector inverse transformation

meshm

minaxis