ILMSImage Attribute Calculation
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! width="5%" | Attribute type !! width="12%" | Attribute !! width="12%" | GUI-Label !! width="16%" | Internal designation !! width="55%" | Description | ! width="5%" | Attribute type !! width="12%" | Attribute !! width="12%" | GUI-Label !! width="16%" | Internal designation !! width="55%" | Description | ||
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| − | | | + | | basis || average value per band || ''average value per input band'' || <code><layer_id>[_<numerator></code>] || For every input band an average value is calculated from all image pixels summarized in one cell. The internal designation corresponds to the identifier which is selected for the corresponding band (in the example: <code>panchromatic</code>), in case of mult-channel input data completed by one channel number (in the example: <code>multi-spectral_1</code>, <code>multi-spectral_2</code>, etc.). |
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| rowspan="4" | structure || linear texture || ''linear texture'' || <code>linear</code> || The activation of this measure creates the 1st degree texture in a 3x3 kernel. The algorithm calculates the texture for every cell individually and ignores all image pixels which are outside of the current cell. Like all structural features also the linear texture uses the first channel which is displayed in the project information as a basis for calculation. | | rowspan="4" | structure || linear texture || ''linear texture'' || <code>linear</code> || The activation of this measure creates the 1st degree texture in a 3x3 kernel. The algorithm calculates the texture for every cell individually and ignores all image pixels which are outside of the current cell. Like all structural features also the linear texture uses the first channel which is displayed in the project information as a basis for calculation. | ||
Revision as of 11:39, 29 August 2011
Contents |
50px| ILMSImage Attribute Calculation
Introduction
ILMSImage Attribute Calculation is part of the ILMSImage plug-in for QuantumGIS and is used for the derivation and calculation of cell-based attributes and for the integration of additional data layers.
Similar to various ILMSImage panels it consisits of two components, ILMSImage Project Information in the upper section and the actual tools in the lower section.
Das ILMSImage-Panel zur Berechnung von Zellattributen
Attribute Calculation
Background
...
Overview
The panel allows the following functions for the user:
- Calculation of default cell-based attributes: In addition to features of cell geometry basic attributes, different structural features and statistical measures belong to the implemented parameters. After the calculation those are summarized in form of an attribute table.
- Adding additional data layers: The corresponding data layers are selected by the user, an identifier is assigned and added to the existing data layers. If necessary, the data type is automatically adapted and the selected additional data are cut in terms of space.
- Visualization of selected attributes: For this purpose the attributes which are summarized in a database table are transformed into raster data and prepared in QuantumGIS for visualization.
Calculation of Cell-Based Attributes
In order to derive specific attributes for the samples from the link of cell geometry and selected input data, the relevant parameters have to be activated by clicking on the corresponding check box. The default attributes are basic values, structural features, statistical parameters and the implicitly calculated features of cell geometry.
| Attribute type | Attribute | GUI-Label | Internal designation | Description |
|---|---|---|---|---|
| basis | average value per band | average value per input band | <layer_id>[_<numerator>] |
For every input band an average value is calculated from all image pixels summarized in one cell. The internal designation corresponds to the identifier which is selected for the corresponding band (in the example: panchromatic), in case of mult-channel input data completed by one channel number (in the example: multi-spectral_1, multi-spectral_2, etc.).
|
| structure | linear texture | linear texture | linear |
The activation of this measure creates the 1st degree texture in a 3x3 kernel. The algorithm calculates the texture for every cell individually and ignores all image pixels which are outside of the current cell. Like all structural features also the linear texture uses the first channel which is displayed in the project information as a basis for calculation. |
| normalized texture | Normalized texture | normalized |
The normalized textures uses the same algorithm as the linear texture but it normalizes the result additionally with the average value of all image pixels of the current cell. Like all structural features also the normalized texture uses the first channel which is displayed in the project information as a basis for calculation. | |
| Inverse texture | inverse texture | inverse |
By activating the inverse texture the Inverse Difference Moment (Haralick et al. (1973), S. 619) is calculated on pixel level. Inverse texture uses the same algorithm as the linear and normalized texture but it finally calculates the inverse value of the square differences. Like all structural features also the inverse texture uses the first channel which is displayed in the project information as a basis for calculation. | |
| Laplace texture | Laplace texture | laplace |
This structural feature uses the modified Laplace kernel for contrast enhancement for individual cells. The parameter enhances the result with a generic kernel which reacts to local contrast maxima with minimal spatial distance (two to five pixels). As a result, isolated lines are reduced and regions are filled with spatially dense contrasts. | |
| statistics | standard deviation | standard deviation | stddev |
By activating this option the standard deviation of all image pixels summarized in one cell of the first channel in the project information is calculated. |
| cariance | variance | variance |
By activating this option the variance of all image pixels summarized in one cell of the first channel in the project information is calculated. | |
| cell geometry | cell size | without GUI link | size |
The size of one cell in image pixels of the most highly resolved input data channel. |
| cell perimeter | perimeter |
The perimeter of one cell in image pixels of the most highly resolved input data channel. | ||
| cell length | length |
The length of a cell in image pixels of the most highly resolved input data channel. | ||
| cell width | width |
The width of a cell in image pixels of the most highly resolved input data channel. |
After the selected attributes have been calculated, they are summarized in a table and are available for additional analysis using ILMSImage. The user receives a note about the end of the process and a summary of the calculated attributes.
Benachrichtigung bei Abschluss der Attributberechnung
Export and Visualization of Cell-based Attributes
For visual control the plug-in makes it possible to export selected attributes as raster layers after they have been calculated and to show them subsequently in the current QuantumGIS-Project. Consequently, the required attributes are selected and the process is started by clicking on Export/visualize attributes. Then ILMSImage creates raster datasets of the attributes and stores them in the exports directory of the current ILMSImage project. The completion of the process is indicated to the user in a message window.
Benachrichtigung und Abfrage nach Abschluss des Attributexports
The window also offers the possibility of visualizing all exported attributes automatically. For this purpose the raster datasets are loaded into the current QuantumGIS project, relocated to the key group for ILMSImage Exports and their visualization is adapted by using a Standard Deviation Stretch. The result is represented in a map view like this:
800px|Exportierte und in der Kartenansicht visualisierte Attributdatensätze
If the corresponding prompt is denied, the exported attributes can be added to the current QuantumGIS project individually and separately by the user. In this case, the visualization has modified by the user as well.
Working with External Data Layers
Adding and Editing Additional Data Layers
In addition to the mentioned standard attributes, the external data layers can be integrated into the process of attribute calculation. For the integration basically every available dataset in raster form is suitable. In the integration within every layer and for every cell a mean value is calculated and finally added to the attribute table. This means that additional attributes correspond to the above-described basic attribute - with regard to the calculation ordinance – the only difference being that additional data layers do not influence cell creation since they are already completed. This function is therefore suitable for integrating additional multispectral levels (or combinations of these) which are required as attributes for additional analysis but not for a derivation of analysis areas, i.e. cells, into the work process. A simple example is the Normalized Vegetation Difference Index, NDVI which is a measure for vegetation activity. It can be calculated using two channels which are in the visual field and in the close infrared field of the electromagnetic spectrum. As additional data layer a pixel-based NDVI picture is available. The following image shows areas of high vegetation activity in green colors and areas of low activity in yellow colors.
800px|In die Kartenansicht geladener pixelbasierter NDVI-Datensatz
This dataset can now be defined as an external data layer - for this purpose it does not have to be loaded in QuantumGIS; it is sufficient to know the corresponding path. For the definition the corresponding field of the pnale is used. The tool allows to define new external layers (1), edit existing layers (2) and delete external data layers from the project (3).
Tool zur Definition und Bearbeitung externer Datenebenen
Um einen neuen externen Layer anzulegen, erscheint nach Klicken auf das entsprechende Icon ein Dialogfenster, das es erlaubt, die betreffende Datenquelle über das Dateisystem auszuwählen und einen Bezeichner zu vergeben. Dabei sollte darauf geachtet werden, dass ein wirklich eindeutiger Bezeichner gewählt wird, der nicht schon für einen der anderen Datenlayer oder für eines der Standardattribute verwendet (siehe obige Tabelle) Verwendung findet. Für den beispielhaft verwendeten NDVI-Datensatz sieht das folgenderweise aus:
Definition einer neuen externen Datenebene
Nach der Bestätigung wird der Datensatz ins Projektverzeichnis - um ILMSImage analog zu den Quelldateien für die Zellbildung exklusiven Zugriff zu gewährleisten - kopiert. Dabei wird er nach Bedarf auf das Untersuchungsgebiet zugeschnitten. Um eine visuelle Kontrolle zu erlauben, bietet ILMSImage an, das Ergebnis dieses Prozesses in die Kartenansich zu laden.:
Benachrichtigung nach Abschluss der Definition einer externen Datenebene
Nach Bejahung der Frage wird der externe Datensatz mittels eines Standard Deviation Stretch visualisiert, für die Originaldaten bestehende Farbpaletten werden nicht verwendet. Da diese Darstellung nur zur visuellen Kontrolle dienen soll, wird der entsprechende Datensatz vor Durchführung einer Attributberechnung aus der Kartenansicht entfernt. Außerdem erscheint die erzeugte Zusatzebene in der entsprechenden Liste des Werkzeugpanels. Im folgenden Bild werden Areal hoher Vegetationsaktivität in helleren, solche niedrigerer Aktivität in dunkleren Tönen dargestellt:
800px|Zur visuellen Kontrolle geladener externer NDVI-Datensatz
Ein bereits erstellter externer Datensatz lässt sich durch Klicken auf das entsprechende Symbol bearbeiten. Dabei ist eine Änderung des Bezeichners und die Anpassung des Pfades zur Quelldatei möglich.
Automatische Skalierung des Datentyps externer Datenebenen
ILMSImage erlaubt nur Eingangsdaten, die im Byte-Wertebereich (8bit, Grauwert zwischen 0 und 255) vorliegen. Wird bei der Definition einer externen Datenebene ein nicht kompatibler Layer ausgewählt, so erkundigt sich ILMSImage, ob dieser automatisch auf den erlaubten Wertebereich skaliert werden soll. Ist zum Beispiel ein in 16bit vorliegender Teil einer RapidEye-Szene zu integrieren, erscheint die folgende Benachrichtigung:
Benachrichtigung bei Integration eines Layers mit inkompatiblen Datentyp
Nach Bestätigung dieser Nachfrage wird der Datensatz auf den 8bit-Wertebereich skaliert und - wiederum optional - zur visuellen Kontrolle in die Kartenansicht geladen.
Attributberechnung mit externen Datenebenen
Die definierten externen Datensätze stehen wie die ursprünglichen Quelldaten zur Berechnung von Attributen zur Verfügung und werden in der Folge als gleichwertige Layer behandelt. Das gilt für die eigentliche Berechnung und die Visualisierung der berechneten Layer.
Benachrichtigung nach Abschluss der Attributberechnung mit externen Zusatzebenen
Abfrage zur Visualisierung von mit Zusatzebenen berechneter Attribute
Entfernen externer Datenebenen
Um eine externe Datenebene aus dem Projekt zu entfernen, wird diese in der Liste aller externen Layer selektiert und auf das entsprechende Symbol im Panel geklickt. ILMSImage fragt daraufhin, ob der dazugehörige Datensatz dauerhaft gelöscht, d.h. aus dem Dateisystem entfernt, werden soll. Diese Nachfrage bezieht sich nur auf die vorher im Projektverzeichnis erzeugte Arbeitskopie des externen Layers. Die original zur Definition verwendeten Dateien sind von einer Löschung nicht bedroht.
Abfrage beim Entfernen eines externen Layers aus dem ILMSImage-Projekt
Weiteres Vorgehen
Nach der Attributberechnung setzt sich eine typische ILMSImage-Prozesskette mit der thematischen Klassifikation fort, die im Panel ILMSImage Classification realisiert ist.
