The PANCROMA Landsat Point Spectrum Generator (PSG) is a Landsat spectral analysis utility that allows you to interrogate a Landsat band data set and to generate a spectrum that corresponds to points that you select from the set. This can be a powerful tool for mineral exploration or land use analysis when combined with the Landsat Spectral Analyzer described above.
Previous articles have described the PANCROMA Point Spectrum tool for generating spectral data from selected pixels in multispectral data sets. It is often helpful to be able to zoom into an image in order to identify and select pixels of interest to add to the Point Spectrum list. PANCROMA has a utility for doing this. In order to use the zoom tool, open your multispectral images as described in the previous articles describing the Point Spectrum generator. When the Point Spectrum Form becomes visible, you will see two radio buttons labeled 'Zoom Enabled' and 'Zoom Disabled', as shown below.
When the 'Zoom Disabled' radio button is checked, data entry works as described previously. That is, each time you click on the multispectral band image, a data point corresponding to that pixel location will be added to the list.
However, when 'Zoom Enabled' is checked, data will no longer be added to the Point Spectrum list when you click on the grayscale band image. Instead, clicking on the image will identify the zoom center and enable the Zoom menu. When you select your zoom center by clicking on an area of interest in the image, select 'Display' | 'Zoom In'. A zoomed image will be created in a new graphics window, centered on the point that you clicked. (Note: in order to avoid attempting to compute zoom data for pixels off the edge of the image where no data exists, the zoom center will be automatically moved back from the image borders if necessary. In this case you may have to scroll the zoomed image a bit to locate you zoom center.)
Note that the pixels in the zoom window track those of the source image as you move your cursor. In order to add points to the Point Spectrum list, select the 'Zoom Disabled' radio button. This will allow points that you select from either image to be added to the Point Spectrum list. You can go back and zoom more deeply into the image by re-checking the 'Zoom Enabled' button, which will suspend the addition of points to the Point Spectrum list again and allow the identification of new zoom centers on either image.
Note that it is possible to display an RGB true color or false color image to aid in the location of points of interest. To do this, open the three band files of interest by selecting 'File' | 'Open'. Once all three files are opened, check the 'Maintain RGB Comparison Image' check box at the bottom of the Main Window. Then select 'Band Combination | Generate RGB True Color Composite'. Two RGB images will be displayed select 'Close Graphics Window and Reset'. The RGB form will close, leaving the Comparison Image open. Now you can process your band file data as usual. An example screen shot of an RGB false color composite, band image and zoom image is shown below.
See the PANCROMA Instruction Manual for more information on the zoom utilities.