Spectral Angle Mapper, SAM, is a classification method for comparing the similarity between different spectra. SAM calculates an angle, d, between the vectors of the compared spectra. The angle is calculated from the direction of the compared vectors, which means the SAM algorithm is not sensitive to varying illumination. SAM should be used on reflectance data only.

1. In Evince, SAM can be used for making selections. The SAM selection dialog appears for Contour 2D, 3D and RGB Image plots of original image data when choosing "Selections" from the plot menu. The SAM selection dialog contains a spectrum showing the current selected observation/pixel. The user can mark another selection in the plot and the spectrum in the SAM dialog will be updated instantly. The user will also have to give the angle threshold, which will set all pixels with an angle under the threshold to selected. The "Select" button at the bottom left of the dialog is used for making the selection in the plot.

2. SAM can also be used to create a spectral angle map from a Contour 2D, 3D or an RGB image plot of the original data . Use the point selection to select a point and right-click on the plot to access the plot menu. From the advanced menu item, select Create spectral angle map.

A dialog where the spectral angle map is created appears. The user can choose to create a Contour 2D, a Contour 3D or both plots from the image data. The Contour 2D will show a spectral angle map where white areas are pixels with very similar spectral properties as the selected pixel. The Contour 3D will show a spectral angle map where areas with a high altitude are pixels with very similar spectral properties as the selected pixel.

The figures below show the Contour 2D Spectral Angle Map to the left and the Contour 3D Spectral Angle Map to the right.