Raster maps, polygon maps, segment maps, point maps, tables and columns are called data objects.
Raster maps
A raster map consists of pixels (picture elements) of a certain size, e.g. 20m x 20m. Pixels are either codified by IDs, class names, values, or colors; this is determined by the domain of the map. A raster map should have coordinates, that is a georeference. In ILWIS, most spatial operations are performed on raster maps.
To obtain a raster map:
Polygon maps
A polygon map is a vector map containing closed areas and the boundaries making up the areas. Polygon maps can for example contain uniquely codified areas such as cadastral plots, or mapping units such as land use classes, geological units or soil units. The areas are either codified by IDs, class names or values; this is determined by the domain of the map. Further, a polygon map uses a certain coordinate system.
Polygon maps are generally used as a stepping stone to raster maps.
To obtain a polygon map, you first have to create a new segment map and edit it with the segment editor (with or without digitizer); then polygonize these segments within the segment editor or with the Segments to Polygons operation.
Segment maps
A segment map is a vector map containing lines (for example roads, rivers or contour lines). Segments are either codified by IDs, class names or values (height map); this is determined by the domain of the map. Further, a segment map uses a certain coordinate system.
To obtain a segment map, you should create one and edit it with the segment editor (with or without digitizer).
Point maps
A point map contains points, for example water wells or sample points. Points are either identified by IDs, class names or values; this is determined by the domain of the map. Further, a point map uses a certain coordinate system.
To obtain a point map you should create one and edit it with the point editor (with or without digitizer).
(Attribute) Table
A table consists of records and columns. A table is an attribute table when the table stores additional information on elements in a map; i.e. extra tabular data which relates to mapping units, points, segments, or polygons in maps.
Raster, polygon, segment and point maps of the domain type Class or ID can have attribute tables. The domain of the attribute table should be the same as the domain of the map to which it relates. An attribute table can be linked to a map or to a domain through the Properties of a map or a domain.
An attribute table can be edited when the table is displayed in a table window. When the table is linked to a map or to a domain, and the map is displayed in a map window, you can also double-click the units in the map.
Columns
A table consists of columns. You can perform calculations with columns using TabCalc.
Each column has a domain. A column with a value domain contains values, a column with a class domain contains class names, a column with domain ID contains IDs, etc. Columns can also have domain String; you can use this to type for instance descriptions.
If in an attribute table you have columns with a class domains, or with user-defined value domains, you may consider to prepare a representation for these columns as well. When you open the map to which the attribute table is linked, you can directly display the map by one of its attributes.
Map lists, object collections, map views, layouts, annotation text objects and graphs are called container objects.
Map lists
A map list is a set of raster maps, for example the bands of a satellite image. All raster maps in the map list must have the same georeference and the same domain.
A map list is used for:
A map list can be created from the File menu in the Main window or while starting an operation which requires a map list as input. You can include as many maps in a map list as you like.
Object collections
An object collection is a set of ILWIS objects.
An object collection only stores the names and locations of the object definition files of the maps, tables, etc. that are included in the object collection. The object definition files of these maps, tables, etc. contain further references to the names and locations of the data files on disk.
Object collections:
Furthermore, a special case of object collections are database collections. Database collections are the result of accessing an external database, and only contain the Use As tables u of the external database. For more information, see ILWIS objects : tables - databases.
Map views
A map view is a saved map window.
In one map window, you can display:
When you save a map window as a map view, all layers in the map window and their display settings as well as the georeference of the map window are stored. When you open a map view later on, the map window will appear exactly as it was saved. You do not need to add individual maps to the map window anymore, nor specify their display options.
Map views MUST be created when you wish to print maps. After saving the map window(s) as map view(s), create a layout to which you can add one or more map views and additional annotation such as legends, north arrows, scale bars and scale texts, texts (such as a title), map borders including ticks and coordinates for grid lines or a graticule, a page border, boxes, bitmaps and pictures.
Mind: A map view in a layout may only contain one raster map.
In the layout editor, you can then make a final composition of the map views and the annotation.
Layouts
A layout is required to print maps with optional annotation. A layout is a virtual sheet of paper on which you can make a composition of one or more map views, specify the scale on which these map views should be printed, and on which you can insert annotation.
In the layout editor, you can add to a layout:
For each map view, you can add to the layout:
Tip:
To obtain a layout, first save a map window containing one or more maps, optionally Annotation Text, grid lines and/or graticules as a map view. Then, create a layout and add one or more map views to it.
Annotation Text
An Annotation Text object, also called an annotation text layer, is designed to display and store multiple texts (such as labels of points, segments or polygons) at multiple positions.
Tip:
When one or more maps, annotation text layers, optional grid lines and graticules that are displayed in a map window are saved as a map view, and when the map view is added to a layout, you can add further texts (such as a title) to the layout.
Graphs
A graph can be created from columns in a table.
You can either create a so-called graph from columns (displayed as points, bars, line, step or needle), or a rose diagram. The graph will be shown in a graph window.
After you displayed a graph from columns, you can add graphs from formula, a least squares fit, or a semi-variogram model. In the graph window, the different graph layers will appear in the Graph Management pane.
A saved graph contains all necessary display options to redisplay the graph after the graph window has been closed.
For more information, refer to Graph window : functionality, Graph window : examples of graphs, or Graph window : Graph Management pane.
Domains, representations, georeferences, and coordinate systems are called service objects.
Domains
A domain is a set of possible values of a variable. In ILWIS, a domain is the set of possible IDs, class names, or values that can be used for instance in a map. All maps, tables and columns (data objects) have a domain; a domain is a service object for maps, tables and columns. One domain can be used for several data objects.
The four main types of domains are:
for data objects which contain unique identifiers (e.g. plot 1024, plot 1025) |
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for data objects that contain classes (e.g. soil units: clay, sandy loam) |
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for data objects that contain measurable, calculated or interpolated values (e.g. height, concentration) |
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for satellite images containing values between 0 and 255. |
Maps which use a class, value or the image domain can have a user-defined representation.
Representations
A representation generally defines the manner in which the classes of a map with a class domain, or the values of a map with a value domain or the image domain should be represented on the screen and on a printer. A representation is a service object for a domain, i.e. a domain uses a certain representation. For maps which have a specific meaning (e.g. land use classes or height values) and which need fixed colors, it is advisable to create a user-defined domain and a user-defined representation. Maps which use the same domain are by default displayed in the same colors.
Representation types:
Georeferences
A georeference is a service object which stores the relation between rows and columns of a raster map (row,col) and coordinates (X,Y). A georeference is needed for raster maps. A georeference uses a coordinate system. It is advised that raster maps of the same area use the same georeference.
To combine raster maps with different georeferences, for instance in MapCalc or Cross, first use the Resample operation, so that all maps will use one georeference.
Coordinate systems
A coordinate system defines the possible XY- or LatLon-coordinates that can be used in your maps and thus stores information on the kind of coordinates you are using in your maps. You may for instance use user-defined coordinates, coordinates defined by a national standard or coordinates of a certain UTM zone. Point, segment and polygon maps always have a coordinate system. Raster maps have a georeference which uses a coordinate system. A coordinate system is a service object for point, segment and polygon maps, and for georeferences of raster maps.
There are five main types of coordinate systems:
Tip:
It is advised to use one coordinate system for all your maps. In case you have data of different sources in different projections, it is advised to transform all data to one common coordinate system.
Histograms, sample sets, stereo pairs, criteria trees, two-dimensional tables, matrices, filters, functions, scripts are called special objects.
Histograms
A histogram is a special object which lists frequency information on values, classes or IDs in a raster, polygon, segment or point map. A histogram is automatically calculated when displaying a value map with stretching; you can also use the Histogram operation.
In a histogram window, a histogram is presented as a table and as a graph.
Summary information of a value histogram, such as mean, standard deviation, and intervals, can be viewed both in the histogram window as well as in the Properties of the histogram.
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A raster histogram lists the number of pixels, the percentages and the areas per value, class or ID. If the input raster map uses a domain Value, also cumulative number of pixels and cumulative percentages are calculated. |
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A polygon histogram lists the number of polygons and the perimeter and area of polygons per class, ID, or value. If the input polygon map uses a Value domain, also the cumulative number of polygons, cumulative perimeters and cumulative areas are calculated. |
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A segment histogram lists the number of segments and their length per class, ID or value. If the input segment map uses a Value domain, also the cumulative number of segments and cumulative lengths are calculated. |
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A point histogram lists the number of points per class, ID or value. If the input point map uses a Value domain, also the cumulative number of points are calculated. |
Sample sets
Prior to an image classification, sample pixels or training pixels have to be selected in a sample set. To create a sample set, first a map list and a domain have to be specified. Then, with sampling, assign class names to groups of pixels that are supposed to represent a known feature on the ground and that have similar spectral values in the maps in the map list.
A sample set contains:
When your graphics board is configured to use 256 colors, you can locate your training pixels on a background map, for instance a color composite. In case your graphics board is configured to use more than 256 colors, you will use an interactive color composite; then, a background map is not used.
Stereo pairs
A stereo pair is calculated from a pair of input raster maps, for instance two aerial photographs with overlap, the fiducial marks of the photographs, the principal point of each photograph, the transferred principal points, and optionally one or two scaling points.
A stereo pair is automatically calculated when it is opened for display. The stereo pair then contains:
A stereo pair can be displayed:
To create a stereo pair, use the Epipolar Stereo Pair operation.
Criteria trees
A criteria tree contains the definition of a complicated calculation in which multiple input maps and/or attribute columns are combined, according to certain user-defined rules or criteria, to obtain a final output raster map using Spatial Multi-Criteria Evaluation (SMCE).
Under the main goal of a criteria tree, you can add:
A criteria tree as a whole contains all rules you defined; it thus contains the way in which all input data should be standardized, grouped or weighed, to be able to calculate the final output map. The calculated final output map will show the performance of an area for the main goal that was set.
To build a criteria tree, you need to:
Optionally, you can calculate performance by multiple scenarios or alternatives, in order to select the best scenario or alternative, and to identify poorly performing scenarios or alternatives. You will use:
Two-dimensional tables
A two-dimensional table is used to combine two raster maps with class or ID domain. It defines a new value for each possible combination of input classes or IDs.
A two-dimensional table view consists of rows which represent the domain of one map and of columns which represent the domain of another map. You have to assign a new value, class name or ID to the fields which represent the combination of the domains. Then you have to apply the two-dimensional table on the command line of the Main window. The output raster contains the values, classes or IDs as entered in the two-dimensional table.
Matrices
A matrix is a 2-dimensional array of values. Matrices are calculated by the Principal Components operation and by the Factor Analysis operation. The Principal Components operation calculates a.o. a variance-covariance matrix and the Factor Analysis operation calculates a.o. a correlation matrix. The matrices can be shown.
In the properties dialog box of a matrix, some additional information of the matrix can be viewed namely the total variances in the output bands.
Filters
Filters are used in the Filter operation.
ILWIS offers you:
Functions
Functions can be used in all calculators in ILWIS: MapCalc, TabCalc, scripts and the pocket line calculator. Some 50 internal functions are available (see also Map and Table Calculation), but also user-defined functions can be created.
A user-defined function may contain any combination of operators and functions, and may use parameters representing maps and columns. Parameters in a user-defined function can have any name.
Scripts
A script is a sequence of ILWIS expressions. By creating a script, you can build a complete GIS or Remote Sensing analysis for your own research discipline. Scripts are equivalent to batch files in ILWIS version 1.4.
For more information about scripts, see ILWIS objects : scripts. For more information on script syntax, see Map and Table calculation, Appendices : ILWIS expressions and Appendices : ILWIS script language (syntax).
See also: