Mapping Toolbox

geographic data structure

Define specially formatted structure containing data for map objects

Description

Data for map objects can be stored in a specially formatted structure called a geographic data structure, which allows for easy display, manipulation, and extraction of map data. The Mapping Toolbox provides the displaym, extractm, and mlayers tools specifically designed to be used with such structures.

A geographic data structure can be defined for six different types of map objects: lines, patches, regular surfaces, general surfaces, text, and light objects. A specific set of fields is required for each different type of map object. Each of these required fields must exist for each element in the structure. However, fields that are not essential for displaying the object can be left empty. For example, the otherproperty field must exist, but can be an empty cell array. Listed below are the six types of map objects along with their required fields.

line	type, tag, lat, long, altitude, otherproperty
patch	type, tag, lat, long, altitude, otherproperty
regular	type, tag, map, maplegend, meshgrat, altitude, otherproperty
surface	type, tag, map, lat, long, altitude, otherproperty
text	type, tag, lat, long, altitude, string, otherproperty
light	type, tag, lat, long, altitude, otherproperty

The type field must be one of the specified map object types: 'line', 'patch', 'regular', 'surface', 'text' or 'light'.

The tag field must be a string different from the type field usually containing the name or kind of map object.

The lat, long, and altitude fields can be scalar values, vectors, or matrices, as appropriate for the map object type.

The map field is a matrix map. If map is a regular matrix map, maplegend is its corresponding matrix map legend, and meshgrat is a two-element vector specifying the graticule mesh size. If map is a general matrix map, lat and long are the matrices of latitude and longitude coordinates.

The otherproperty field is a cell array containing any additional display properties appropriate for the map object. Cell array entries can be a line specification string, such as 'r+', or property-value pairs, such as 'color','red'. If the otherproperty field is left as an empty cell array, default colors are used in the display of lines and patches based on the tag field.

Examples

The layermtx workspace contains five different geographic data structures:

• load layermtx
  whos
    Name             Size         Bytes  Class
    cities           1x10         15956  struct array
    citymarker       1x10          7048  struct array
    lights           1x2           1798  struct array
    matrixmaps       1x2         141414  struct array
    topostruct       1x1         519342  struct array
  

The citymarker structure contains ten elements, each consisting of the required fields for a line object:

• citymarker
  citymarker = 
  1x10 struct array with fields:
      lat
      long
      type
      tag
      altitude
      otherproperty
  

The first element contains data for a Cape Town city marker. Note that the altitude field can be left empty:

• citymarker(1)
  ans = 
                lat: -34
               long: 18.30000000000000
               type: 'line'
                tag: 'Cape Town'
           altitude: []
      otherproperty: {1x1 cell}
  

The otherproperty field indicates that the city marker for Cape Town will be a blue asterisk:

• citymarker(1).otherproperty
  ans = 
      'b*'
  

See Also

displaym	Project data in a geographic data structure
extractm	Extract vector data from a geographic data structure
mlayers	GUI for manipulating map layers

geod2rec

geoid vector