Shift to Marker Dialog
In the "Shift to Marker" operation, a Navigator point is added at a feature on an image, then the feature is found in an image at some higher magnification, and the green marker point is placed on the feature. The program can then compute the amount that the Navigator item's stage position needs to be shifted so that it corresponds to the feature's position at the higher magnification. In the simplest (and original) use of this operation, the coordinates of all Navigator points are shifted. This kind of global shift is appropriate when a single low magnification map is taken and needs to be shifted to give correct positions at a medium magnification, or when the grid position has been perturbed without rotation, so that a global shift is sufficient to restore Navigator positions. However, the greater flexibility provided here is needed to be able to use the procedure conveniently at multiple magnifications or when maps to be shifted do not all exist at once.
The first set of choices are whether to apply the measured shift to all maps at the registration of the image with the marker point, or to ones only at one magnification. The latter approach is useful when you want to shift the coordinates of medium-magnification maps so that high magnification targets come out centered, without shifting an already-corrected low-magnification map. This is important if you need to pick more positions on the low-magnification map. Whenever shifts are applied to Navigator items just at one magnification, the program keeps track of which maps are shifted by assigning them a common "shift cohort" ID, and it also shifts points and polygons that have been drawn on those maps.
The second set of choices determine whether the measured shift is saved for reuse with the Apply Saved Shift command. Saved shifts are useful if maps being shifted at a particular magnification are not all available at once. Newly obtained maps can be easily shifted by the same amount as previous ones by using a saved shift. A shift is saved specifically for the magnification at which the Navigator item is marked and the magnification of the image with the marker point. A saved shift can be used only for maps taken at the lower magnification and the items marked on them. The saved shift is used through the Navigator menu item Apply Saved Shift, not by opening this dialog.
See the Scenarios section below for some examples of applying these operations in different situations.
Which items to shift
All items at the registration of the image with marker point: This is the original behavior, before this dialog existed. With this option, the only way to control which items are shifted is by changing the registration.
All maps at Yx and items marked on them: The magnification shown in place of Y is that of the current item (if it is a map) or of the map on which it was drawn. This option is appropriate if you wish to protect already-shifted items at other magnifications from being shifted, and if it is acceptable to shift all maps at the magnification in question.
The third option will appear as:
Only maps at Yx and marked items that have not been shifted before if the map that the current item was marked on has not been shifted previously, or as:
Only maps at Yx and marked items that were shifted along with the map that the current item was marked on if that map has been shifted.
The first variant is useful if you are applying the shift routine from scratch to a newly acquired set of maps. The second variant is useful if you use the Apply Saved Shift command for an initial shift of new maps, then use Shift to Marker to refine that shift. In either case, maps will be shifted regardless of whether there are any points marked on them. The process of including items to shift involves three levels of association:
Saving shifts for reuse
These options are available only when shifting items at a specific magnification.
Do not save shift for reuse: existing saved shifts, if any, will not be affected.
Save shift to apply again from Yx to Zx or other higher mag: The first magnification value is that of the map the current item was marked on; the second one is that of the image with the marker point. If a shift is already saved for this pair of magnifications, it will be replaced; otherwise a new one will be saved.
Add to saved shift from Xx to Yx: This option will modify the indicated shift and is useful if you wish to refine a saved shift after using it so that it might be more accurate on another new set of maps. The text (non-matching higher mag) appears if the current higher magnification is not the same as the one when that shift was saved. Adding to a shift in that case would be appropriate if the two higher magnifications are well-aligned.
Scenarios for Using Shift to Marker