The GRALE Editor allows you to select the points which should be used in an inversion procedure. This is of course much easier if there's a FITS or color image (JPG/PNG) to guide you, and this screencast shows how to set such a background. You can add a number of so called layers, containing a FITS image, color image or image points, and which are shown on top of each other. In this screencast only the 'image layer' type is used, which is meant to display an astronomical image in some format. The other type, 'points layer' is meant to store points belonging to the same gravitationally lensed image. So first, we'll add an 'image layer' and double click 'Load image' to load a FITS image. To adjust the way the values in the FITS image are translated to visible pixels, change the 'Min' and 'Max' values. The image is automatically centered on the center pixel, but typically one would like to change this. To do so, select the 'Center image' tool and double click the point that you'd like to have as the center. The center coordinates that are visible in the layers window are in degrees and are derived from the WCS coordinates stored in the FITS image. You can zoom in and out using the scroll wheel of your mouse. Since some features are more easily visible in another frequency range, we'll load a FITS image observed with another filter as well. By toggling the check box in front of the layer you can select which layers are visible and in this case it shows that the two layers are not properly aligned. To align them, we need to make sure that both FITS images are centered on the same coordinate, which we can do by copying and pasting the values. Afterwards the images are clearly well aligned. It may be possible that you've created a color image as well in which some lensed features may be easier to detect/select. For this reason it is possible to load a JPG or PNG as well. Most often, this image will not be aligned with the FITS images, as is obvious in this example. To align them, you can select points in the color image and corresponding points in a FITS image, and instruct the program to align them as well as possible. Selecting such points is done with the 'Point match tool'. WARNING: make sure that the layer in which you want to select points is marked as 'Active'. This can be done by double clicking that layer. In the example here, we'll first select a few points in each layer to obtain a rough correspondence. Numbering the points - which is necessary to tell the program which points should correspond to which - is done using the 'Group number' tool. To make the program calculate a tranformation for the color image, double click the 'Match FITS image' text of the color image layer. Make sure that only the FITS layer that contains the other set of marked points is enabled, otherwise the program may not know where to look for a match. When a first correspondence is obtained, we can improve the match using points near the edges. Of course, you can either move points using the 'Select/move' tool, or you can keep adding points in the layers to create a more accurate match.