Classification

From ObjectVision

Jump to: navigation, search

Introduction

Numeric data items (see value types Numerical) can be Numerical or Categorical.

  1. Numerical data need to be classified before it can presented in a map view. Classify means grouping the values of the original distribution in a limited set of classes. A class unit and a class break attribute are used for this purpose, see example 1.
  2. Categorical data does not have to be classified before it can be presented in a map view, as it is already available in a limited set of classes. Still it can be useful to classify also this type of data, e.g. to reclassify groups to Low, Middle and High, see example 2.

For each class of a class unit, visualisation styles (like colors) and labels can be configured. Labels describe the classes in the map view legend or in the table. The combination of class breaks (if necessary), the set of visualisation styles and labels is called a Classification Scheme. Classification schemes in the GeoDMS are usually configured in a Classifications Container.

Classification Schemes

The following examples show the configuration of Classification Schemes for Numerical (1) and Categorical (2) data:

example 1: Numerical data

unit<float32> meter := baseunit('m', float32)
,   cdf   = "Classifications/m_4K/ClassBreaks";
  
unit<uint8> m_4K: nrofrows = 4
{
   attribute<meter> ClassBreaks: DialogType = "Classification",
      [0,200,400,800];
   attribute<uint32> SymbolColor: DialogType = "SymbolColor",
      [rgb(128,255,0),rgb(0,128,0),rgb(0,64,128),rgb(255,0,0)];
   attribute<string> Labels: DialogType = "LabelText",
      ['0 - 200 meter','200 - 400 meter','400 - 800 meter','>= 800 meter'];
}

example 2: Categorical data

unit<uint8> LS_pres: nrofrows = 3
{
   attribute<uint32> BrushColor: DialogType = "BrushColor",
      [rgb(255,255,198),rgb(0,0,200),rgb(0,215,0)];
   attribute<string> Label: DialogType = "LabelText",
      ['Low','Medium','High'];
}

In the first example, a values unit meter is configured with metric: meter. Such quantity values units are usually configured in a Units container. For this values unit a cdf property is configured, referring to a class break attribute, usually called ClassBreaks (or Classes), of a Classification Scheme. By configuring this cdf property, the GeoDMS will use this Classification Scheme by default for all data items with this values unit, to classify the data for the map view. By configuring the cdf property to a data item, the default Classification Scheme configured for the values unit is overruled.

In the first example, the class values unit is a uint8 unit called m_4K. Class units are usually configured in a Classification container. For the class unit, the nrofrows property need to be configured. In the example the class unit has 4 entries.

In the second example the class unit is LS_pres (LandScapePressure). This class unit is also the values unit for items describing the landscape pressure in two classes.

The class units have the following subitems:

  1. ClassBreaks item: The first data item is the item with the class breaks (only for example 1), needed if data must be classified. The values unit of this ClassBreaks item must be the same values unit as the original data item to be classified. In the example this is the values unit meter. The DialogType property for this item needs to be set to Classification. For each class, the start value is configured as primary data (or read from an external storage). In the example the first class starts with the value 0. The class continues until the start value of the next class, in this case 200. The last class is always open ended. The syntax for the data of the ClassBreaks item is: [start value class 1, .., start value class n ]
  2. Visualisation style items, like SymbolColor and BrushColor : The second (set of) data item(s) is used for the visualisation of each class. The DialogType needs to be configured to the specific visualisation style. The possible style items are dependent on the type of data.The current Classification and Palette editor in the GeoDMS GUI only supports adapting colors. Other visualisation style items can at the moment only be configured in the GeoDMS syntax.
  3. Labels item: The last data item is the item with the labels shown in the (map) legend for each class. A labels item need to be configured as an attribute with a string values type. The DialogType property for labels items needs to be set to "LabelText". For each class a label needs to be configured. The syntax for the data of the label item is: [label 1, .., label n].Labels are also shown in the table to refer the data visualized. The current Classification and Palette editor in the GeoDMS GUI supports editing label items.
Personal tools