Definiens Developer 7 - PCI Geomatics

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Definiens Developer 7 - Reference Book3 Algorithms ReferenceImage Layer WeightsImage layers can be weighted differently to consider image layers depending on theirimportance or suitability for the segmentation result.The higher the weight which is assigned to an image layer, the more of its informationwill be used during the segmentation process , if it utilizes the pixel information.Consequently, image layers that do not contain the information intended forrepresentation by the image objects should be given little or no weight.Example: When segmenting a geographical LANDSAT scene using multiresolutionsegmentation, the segmentation weight for the spatially coarser thermal layer should beset to 0 in order to avoid deterioration of the segmentation result by the blurredtransient between image objects of this layer.Thematic LayersSpecify the thematic layers that are to be considered in addition for segmentation.Each thematic layer that is used for segmentation will lead to additional splitting ofimage objects while enabling consistent access to its thematic information. You cansegment an image using more than one thematic layer. The results are image objectsrepresenting proper intersections between the thematic layers.Precondition: Thematic layers must be available.Scale ParameterThe Scale parameter is an abstract term which determines the maximum allowedheterogeneity for the resulting image objects. For heterogeneous data the resultingobjects for a given scale parameter will be smaller than in more homogeneous data. Bymodifying the value in the Scale parameter value you can vary the size of imageobjects.TipProduce Image Objects that Suit the Purpose (1)Always produce image objects of the biggest possible scale which still distinguishes differentimage regions (as large as possible and as fine as necessary). There is a tolerance concerningthe scale of the image objects representing an area of a consistent classification due to theequalization achieved by the classification. The separation of different regions is moreimportant than the scale of image objects.22
Definiens Developer 7 - Reference Book3 Algorithms ReferenceComposition of Homogeneity CriterionThe object homogeneity to which the scale parameter refers is defined in theComposition of homogeneity criterion field. In this circumstance, homogeneity isused as a synonym for minimized heterogeneity. Internally three criteria are computed:Color, smoothness, and compactness. These three criteria for heterogeneity maybeapplied multifariously. For most cases the color criterion is the most important forcreating meaningful objects. However, a certain degree of shape homogeneity oftenimproves the quality of object extraction. This is due to the fact that the compactness ofspatial objects is associated with the concept of image shape. Thus, the shape criteria areespecially helpful in avoiding highly fractured image object results in strongly textureddata (for example, radar data).Figure 7: Multiresolution concept flow diagram.Color and ShapeBy modify the shape criterion, you indirectly define the color criteria. In effect, bydecreasing the value assigned to the Shape field, you define to which percentage thespectral values of the image layers will contribute to the entire homogeneity criterion.This is weighted against the percentage of the shape homogeneity, which is defined inthe Shape field. Changing the weight for the Shape criterion to 1 will result in objectsmore optimized for spatial homogeneity. However, the shape criterion cannot have avalue more than 0.9, due to the obvious fact that without the spectral information of theimage, the resulting objects would not be related to the spectral information at all.Use the slider bar to adjust the amount of Color and Shape to be used for thesegmentation.NoteThe color criterion is indirectly defined by the Shape value.The Shape value can not exceed 0.9.23
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Definiens Developer 7 - PCI Geomatics

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