ILWIS objects

Map lists

A map list is a container object which stores the names of a set of raster maps, for example of the multi-spectral bands of a satellite image that you want to classify. A map list may also store the names of several raster maps of a time series which you can display as a slide show. All raster maps in a map list must have the same the same domain and georeference.

A map list is used:

for sampling and image classification,
for the creation of interactive color composites,
for a principal components analysis or factor analysis,
for the calculation of multiband statistics (variance-covariance matrix or correlation matrix),
to present temporal changes in maps; make a time-series by combining several maps of the same theme but of for instance different years into a map list and show the map list as a slide show.

Furthermore, you can apply a MapCalc formula or an operation on all raster maps in a map list:

the MapCalc formula will be applied to all raster maps in the map list, or
the operations that can use a map list as input are: Aggregate Map, Filter, Stretch, Densify, Resample, Sub-Map of raster map, and Mirror/Rotate.

Another type of map lists can be obtained through Import General Raster. When the image to be imported contains information on multiple bands, and when you use the options Use data in original format, without the creation of separate maps, you obtain a map list which only consists of an object definition file (.MPL). When needed, the actual data will be read on the fly from the original non-converted image.

Names of map lists:

In ILWIS 3, object names comply with Windows long file names. Also Universal Naming Convention (UNC) paths are supported. For more information, see How to use long object names.

To create a map list:

To create a map list, open the File menu in the Main window and select the Create Map List command. You can also expand the Create item in the Operation-tree and double-click the New Map List command, or double-click the New Map List item in the Operation-list. Furthermore, you can also create a map list when you start an operation which requires a map list as input, and click the create button in the operation's dialog box.

In the appearing Create Map List dialog box, enter a name and description for the map list, and select the raster maps you wish to add to the map list. Remember that all raster maps in a map list should use the same domain and the same georeference.

To open a map list:

You can open a map list by double-clicking a map list in a Catalog. A special kind of Catalog will be opened which lists all raster maps in your map list; this is called the map list editor.

To display an individual raster map, double-click the raster map in the map list editor.
To open the map list as an interactive color composite, click the Open as Color Composite button in the map list editor. The raster maps should use the Image domain or another value domain.
To open the map list as a slide show, click the Open as Slide Show button in the map list editor.

To open a map list as a color composite or as a slide show, you can also use the right mouse button on a map list in a normal Catalog, and choose Visualization, as Color Composite or Visualization, as Slide Show from the context-sensitive menu. You can of course also use the Operations menu , the Operation-tree or the Operation-list in the Main window.

When you display a map list as an interactive color composite, you can select which maps of the map list should be used in the color composite and you can specify the stretch ranges for each of the selected maps. By changing the display options of the map list, you can easily change the color composite. This is very suitable for sampling and on-screen digitizing. For more information, refer to How to create a color composite.

When you display a map list as a slide show, one map after the other will be shown in the same map window. This is very suitable to display a time series. For more information on slide shows, see How to display a map list as a slide show or Open map list as slide show.

Tip:

To speed up the display of large raster maps e.g. maps consisting of a few thousand lines and columns or more, you can create Pyramid layers. For more information, refer to ILWIS objects : Raster maps - Pyramid layers.

To edit a map list:

To edit a map list, either double-click a map list in a Catalog, or select one or more map lists in a Catalog and choose Edit Object from the Edit menu in the Main window, or use the right mouse button on one or more selected map lists in a Catalog and choose Open from the context-sensitive menu.

In the appearing Map List editor window, you can:

add other raster maps to your map list for instance by using the Add Raster Map button;
remove maps from the map list for instance by using the Remove Raster Map(s) button;
change the order of maps in the map list (for slide shows) by dragging a map to another position.

For more information, refer to How to edit a map list.

Calculating with map lists/Operations on map lists:

Usually, you will create a map list during sampling to obtain a sample set with which you can perform a supervised classification in a later stage. Sampling however is an interactive process and not a genuine operation.

To apply a MapCalc formula on all raster maps in a map list, you can type a map list expression on the command line of the Main window. For instance, if the regular MapCalc formula on InMap reads:

OutMap = SQ(InMap) + 10

Then, the map list expression to use the formula on all input maps in a map list InMapList reads:

OutMapList = MapListApplic(InMapList, "SQ(##) + 10")

where ## represents the individual raster maps in the map list.

Similarly, operations that use a raster map as input and produce a raster map as output, can also be performed on all raster maps of an input map list. You can choose the input map list in the dialog box of the operation but you can also type an expression on the command line of the Main window. The general syntax of map list expressions for operations is:

OutMapList = MapListApplic(InMapList, MapOperation(##, other parameters))

where ## represents the individual raster maps in the map list.

The output map list is a dependent object. When the output map list is opened, the dependent output raster maps will be defined and calculated. The output raster maps of the map list will obtain the same name as the output map list, followed by _1, _2, _3, etc. For more information refer to Aggregate Map : command line (2), Filter : command line (2), Stretch : command line (2), Densify : command line (2), Resample : command line (2), Sub-Map of raster map : command line (2), or Mirror/Rotate : command line (2).

Furthermore, when you perform a statistical operation on a map list, a matrix is returned containing multivariate statistical information on the values of the different raster maps in the input map list. When you use the Principal Components or the Factor Analysis operation, you will obtain, besides the matrix, also an output map list with output raster maps.

Technical information:

A map list only consists of an ASCII object definition file (.MPL). Normally, the object definition file contains further references to the raster maps that are included in the map list.

In case the map list is the result of Import General Raster using the option Use Data in Original Format and without the creation of separate maps, then the object definition file will only contain a reference to the original non-ILWIS file and there will be no separate ILWIS raster maps stored on disk. When such a map list is opened, the first band is called 'band 1', the second 'band 2', etc.

On the command line, the first band of such a map list can be addressed as maplistname.mpl:1, the second band as maplistname.mpl:2, etc. To calculate with such maps on the command line, you can use for instance expressions like OUT = MyMapList:1 + MyMapList:2 or OUT = 'My Map List'.mpl:1 + 'My Map List'.mpl:2.

By opening the properties of a map list, you can see georeference and the domain used by the maps in the map list, whether the map list is editable or dependent, calculated, etc. You can also see which raster maps the map list contains. For more information, see Basic concepts : properties of objects or the Map List Properties sheet.

In case you calculated a variance-covariance matrix or a correlation matrix, the Properties sheet contains an extra Additional Info tab which shows you the Optimum Index Factor (OIF) of combinations of three bands in the map list. For more information, see How to calculate the Optimum Index Factor.

Limitations:

In principle, the maximum number of raster maps that can be included in a map list is 100 million. In practice however limitations will occur by available disk space.