Raster Snap makes it easy to select points on raster entities when you are using vectorization tools (VTools) or REM commands.
You can use raster snapping to move your AutoCAD cursor precisely to the center, end, corner, intersection or edge of a bitonal raster entity. When raster snapping is on (active), AutoCAD Raster Design toolset displays a snap window around the AutoCAD cursor. This window moves with the AutoCAD cursor and displays the crosshairs over points you can snap to.
Raster snap modes are very similar to AutoCAD object snap modes (OSNAP), except that they snap to raster objects instead of to vector objects. Also, Raster Snap is active only when you are in a command and are being prompted for a point. Raster Snap settings are located on the Raster Snap tab of the AutoCAD Drafting Settings dialog box.
Conflicts can occur between raster snapping and other utilities that control the cursor, such as Mechanical Desktop’s “Ignore Z Coordinate” feature. When a conflict occurs, the application that cannot gain cursor control displays an error message such as “Unable to Register Input Point Filter.” If AutoCAD Raster Design toolset’s Raster Snap interferes with a cursor control feature in another application, you can turn off Raster Snap. If another application is interfering with Raster Snap, consult that application's documentation for details on how to disable the conflicting feature.