Click on this button or the menu item to show the Options tabbed dialogue box:
and you will see:
You can toggle the programme window size along with the use of more than one monitor if installed and enabled by clicking the relevant checkbox. For one monitor, the checkbox shows and for two it changes to The choice becomes effective when the programme is restarted. Changing the window size using the upper right corner buttons and is immediately effective, but the change is not retained for the next programme restart..
Other options are immediately in effect when the options box is closed.
In the left panel, you can choose the appearance of the output image.
Choose Overlay Source + Target White if you have a black and white map and wish to display the black lines of the map in white where they correspond with features in the transformed image.
Choose Overlay Source + Target Black if you have a black and white map and wish to display the black lines of the map in black where they correspond with features in the transformed image.
Overwrite Target uses the input image (Source) to overwrite the output image (Target) after transformation regardless of the colour of the target.
Merge Source with Target places those parts of the input image in areas of the output image which are pure white, leaving the remainder of the output image untouched.
White and Black backgrounds create target images that show only the transformed data on the respective white or black backgrounds.
If you have chosen Mix as an output option, you can choose the percentage of mixture of the source and the target image after transformation with the track bar next to the Mix button.
Insert White Bgd Source-Target means that if a source image pixel is not white, it is inserted into the target, otherwise the target is left as it is.
Insert Black Bgd Source-Target means that if a source image pixel is not black, it is inserted into the target, otherwise the target is left as it is.
These two options are usually used when inserting rectified coloured orthophoto set into a coloured satellite or Google Earth image.
The Xor option gives false colour output which may be useful for testing the visibility of a transformation to an image background like an orthophoto. It is normally not used as a permanent result.
It is recommended to try various options followed by an Undo to see what they do to your data. This must be done without using the Transform and scale option which does not support undo, because it must close the original images before displaying them.
Interpolation and Transformation Options:
The transformation calculates the colour or grey value at the position of an output pixel from the input image. The interpolation option permits choosing the way the pixel value is computed from its nearest neighbours, since the transformed position usually falls in between four adjacent pixels. The speed of calculation for each output pixel depends on the choice of interpolation:
1) Coarse: the colour or grey value of the nearest neighbour to the computed input position is taken. This is the fastest method, but it may produce a jagged appearance in straight line features (aliasing).
2) Medium: the colour or grey value is interpolated bi-linearly dependent on the values of the four neighbours and the distance of the calculated point from them. This is nearly as fast as the nearest neighbour method, but it blurs the result slightly.
3) Fine: the colour or grey value is interpolated from the 16 nearest neighbours of the pixel using an approximation to a sin(x)/x (sinc) function which best preserves fine detail. Since considerably more calculation is required, this is the slowest method.
The programme computes an optimal transformation depending on the number of available control points in the source and target images. For 4 points, a projective transformation is computed. It does not take small errors in the positions of those points into account. For 5 or 6 points, a least-squares error fit is used. If there are 7 to 9 points, a second order non-linear correction is added to the least squares calculation. This compensates to some extent for radial lens distortion and moderate terrain height differences. For 10 to 12 points third order, 13-17 fourth order and 18 or more fifth order corrections are used which improve terrain matching and other smaller differences.
You can restrict calculation to a projective transformation only by choosing Projective, and only the least-squares error routines are used. If you have 7 or more points, you can force calculation to use the higher order corrections.
If you don't want to be bothered by warnings when the reprojection error exceeds 1% of the average side lengths of all images, uncheck the Reprojection Warning box.
File Default Options:
Here in the left panel, you can choose to display either all supported types of image files or only a single type which you select. Similarly, you can choose the type of output file in the right panel. A large number of other types of additional image file types may be chosen and loaded using the file opening dialogue.
Grid calibration options are shown in the upper right corner. Choosing EPSG also requires choice of the appropriate European Petroleum Survey Grid option number from the main menu.
The programme can read and write files for geo-referencing in two popular geographic information systems (GIS), ArcGis and MapInfo. If you have already geo-referenced a map or a satellite or orthophoto in either of these GIS, by reading it in with the GIS option selected, an initial calibration will be carried out. This can be refined later with the programme's calibration options.