The Block Snap tool is sequential, and changes operation as it is used. The sequence is;
drag and snap
stretch and snap
rotate stretch and snap
rotate and snap
Block Snap can be a complicated tool, but it is also very powerful. Thus, we include a detailed step by step description in this section. The purpose of the tool is to allow you to fit by snapping complete shapefiles, selected features in shapefiles, and image files to any location on the map within themselves or to each other. Anything selected will snap to anything visible selected or not. Make the files you are interested in 'snapping to something' selected. Snapping will work on any visible file selected or not. Then if you want only certain features you select these with the standard ArcMap selection tools. After setting up your files and selections run the Block Snap tool. The tool operation is in sequence as follows.
The first time you click the tool sets itself in drag mode. The data you selected is collected regardless of a snap onto a vertex or not. Upon a hit a snap box will be seen at the end of a 'drag' line or snap tail. Do not hold the mouse down. Snap values are set by what is entered in the tolerance box on the EV8 toolbar. You must hit a vertex for the tool to begin the drag mode. If you did not get a hit (no snap tail) the first time try again until you do.
The next click will search for a 'to' point to snap onto. This can be a vertex on any file or outline image in your map. You can double click to set the next point anywhere if you wish to bypass a node snap. In an image file you look for the corners. The graphics follower will move and snap to this second point and a point graphic will be drawn at this location. This point is the reference where the block is either stretched from or rotated around.
The tool will now switch to stretch or rotate mode. The cursor will change. If you wish to stretch or rotate without doing a drag move, then you hit the first snap point (the first hit).
When in stretch or rotate mode you may force the tool to work as one or the other. The next snap point you look for is on the follower graphic, not the original data. On a hit, a new snap box will be seen and a new 'drag' line will begin.
If you hit the point reference created in the second click, the tool switches to rotate mode and the 'drag' line will begin at this point. Otherwise the tool remains in stretch mode with the 'drag' line starting at the last location.
In stretch mode you look for a 'to' point just as you did with the second click above. You can hit and snap to any vertex or image corner. Or you can double click to set the fourth point. The follower graphic will now stretch so that the third snap point snaps to the fourth point. The follower is anchored at the place it was first dragged and snapped and stretched from that point. If you press the Ctrl button while in stretch mode, the aspect ratio will remain fixed, and stretching will occur in the Y direction. If you press the Shift button while in stretch mode, the aspect ratio will remain fixed, and stretching will occur in the X direction. Apply this to image files to preserve image ratio.
This means you are in rotate mode. Your 'to' point is just as described above. You hunt for a hit or double click to force a hit. The follower graphic will now rotate and stretch so the third snap point snaps to the fourth point. If you press the Ctrl button while in rotate mode, the data will only rotate, no stretching will occur.
To finish or start over you Right Click and you get the same dialog box you get when you use any of the move tools.
You can right click any time during the process. For example, to do only a snap move you right click instead of continuing into the stretch/rotate mode.
To mosaic images while preserving the image aspect ratio you snap to the upper left corner of the selected image(s) (the ones you want to move) and drag snap this to the upper right corner of a target image (the one you want to snap to). Then to stretch the bottom of the 'moving' image to match the target you snap onto the lower left corner of the follower graphic then snap this corner to the lower right corner of the target. Sometimes the corner of an image is not where it shows on the map. There can be invisible white space that causes you to miss the snap point. If this occurs you might try increasing the tolerance setting. When you snap to either an X or Y location equal to the X or Y of the reference point, the aspect ratio remains fixed. This is the same as using the Ctrl or Shift button. Remember when working with image files, you should always make a backup copy of the aux file that comes with the image file itself. EV8 will overwrite the aux file when images are repositioned.
Snap Toggle (F6 or TAB)
You do not need to set the snapping tolerance. The default is 4 pixels. However if you want to make the snap box larger you can set a value in the tolerance box. At any time the tool is running you may toggle between vertex snapping, and vertex/boundary snapping by pressing the F6 or TAB button. The cursor will change. In vertex snap, the search is for a vertex only. In vertex/boundary snap the search is for a vertex first, then a boundary. A boundary is a line, polyline or the edge of a polygon. Vertex snap mode is the default.