gvSIG-Desktop 1.1. Manual de usuario.

Click on the “New point” button in the “Georeference” dialogue and go to the view.

Place the mouse pointer over the image to be georeferenced and look for a control point. This point is defined as a red circle with a cross in the middle. If you move outside the boundaries of this image, gvSIG shows an error message and you will have to select a point once again. If you click on the following button

two small windows will drop down. In the left-hand window, the location of the created control point appears over an image zoom, as the following image shows.

If you wish to specify the point further, you can zoom into the image using the zoom tools in the centre of the dialogue box.

If you then click on the point in the mini view and drag it you can move its location.

These changes will automatically be reflected in the gvSIG view.

When you have marked the control point on the image to be georeferenced, this will disappear from the view (this option is marked by default in the "Options" tab in the "Georeference" window and can be modified at any time) and will only leave the base map with the destination point marked on the view.

In this case, the point is defined by a blue square with a cross in the centre.

You can do the same with the mini view on the right as you did with the left, i.e. if you wish to move closer to the point location, you can zoom into the right-hand image and drag the point over the view to place it more precisely.

You can also specify the points in the text boxes in the georeference dialogue window. When the points have been input, press “Enter” and the point will be located in the view.

Remember that the “X” and “Y” text boxes belong to the image to be georeferenced and that “Longitude” and “Latitude” correspond to the georeferenced image. If you have made a mistake with the point and wish to delete it, click on “Remove selected point”.

If you click on this button, a confirmation message will appear.

If you click on "Yes", the point will be deleted. If you wish to remove all the points, click on the “Remove all the points” button.

The control point selection must be repeated as a minimum of three points are required for georeferencing, although at least nine are advisable.

There is another series of tools in the “Georeference” window:

This tool allows you to go to the first control point, to the previous point, search for control points using a pull-down menu, go to the following control point and go to the last pull-down point respectively.

This button allows you to select control points from the view. Firstly, select the control point of the image to be georeferenced and finally, the control point of the destination coordinate.

You can disable an input control point via the "Active” check box in the “Point” tab. This means that the point will not be used in the error and georeference calculations and the symbols will not appear in the view. If you need the point again, you can enable the check box.

If you click on the “Table” tab, a table will appear with all the points and their errors. This table can be enlarged to show more information.