Global Mapper has various snap settings and keyboard shortcuts that facilitate the exacting matching of a vertex with existing vertices or segments while drawing or editing features.
The snap settings and snap tolerance can be set in the Advanced Vector Display Configuration.
To access additional snapping settings described below, activate the Digitizer and right-click to access the Options sub menu.
During some operations (i.e. drawing new area or line features or graphically
placing a new point feature), the cursor can automatically snap to existing
features when you move it near them to facilitate lining up features.
This happens by default unless the ALT or V keys are depressed.
Disables snapping while digitizing.
Enables snapping, only to Area and Line vertices. P Pressing the V key while digitizing also causes only vertices on existing features to be snapped to.
In the 3D viewer hold down the A key to snap to areas, the L key to snap to lines, and the M key to snap to 3d meshes/ models.
Limits snapping to Point features. Holding down the P key causes only nearby point features to be snapped to. This key shortcut is also available when using the digitizer tool in 3D.
Only Snap to Lidar Point Cloud Returns
When this menu item is enabled Lidar point cloud returns will be snapped to when digitizing. This option is disabled by default even when snapping is enabled on the Vector Display tab of the Configuration dialog.
Snap to Pixel Center on Raster Layer
When this menu item is checked, and the data contains one or more raster layers, the cursor will snap to the center of each pixel as it is moved around the view. If the user has enabled snapping to vector features, then the cursor will only snap to a pixel center when it does not snap to a vector feature (i.e., no vector features are nearby.)
You can customize the pixel
radius used when looking for a location on existing features to snap by
creating/ editing the DWORD registry key 'HKEY_CURRENT_USER\Software\Global
Mapper\SnapToPixelRadius'. The default value is 10 pixels. Just create
that registry key and provide the distance (in pixels) to search from
the cursor location for a location to snap to.