Digitising - Snap Modes

(These options are not available in the Freeware version)

The Snap Modes are used in conjunction with the Digitising and Vector Editing features. You will find the snap mode options on the Digitising Toolbar and the Vector->Digitise menu.

A Snap is the name we use to describe the process of placing a vector point onto a drawing feature at an exact location without having to manually enter the precise coordinate. For instance, you can snap onto a Vector end point, a polyline end point, or the centre of a pixel.

Target Square

To show you how the snap modes is working, WinTopo Pro shows a target square at the snap location. The target square jumps onto the nearest snap location as you move the cursor around the drawing. When no snap mode is in operation the target square is shown at the centre of the cursor, like this Digitising cursor.

The target square indicates the coordinate that would be used if you clicked the mouse with the cursor at that position.

Snaps

These are the snap modes which are available.

Snap Off Snap Off
With this button depressed, there is no snapping. Digitised points will be placed at the cursor location.

Snap to Pixel Centre Snap to Pixel Centre
This option causes all digitised points to be at exact pixel locations. If you magnify your image, you will see that the vector end points are shown at the centre of the pixels.

This is useful for digitising horizontal and vertical vectors because it is easy to position a vector end at the same horizontal or vertical position as the vector start point.

This is also useful if you want your vector coordinates to be integral values (no decimal places).

Snap to Vertex Snap to Vertex
This mode causes digitised points to snap onto the ends of existing vectors on the drawing.

This is very useful for ensuring that vectors join at exactly one coordinate.

The Snap to Vertex mode is affected by the Maximum Snap Distance setting in the Digitising Options. So snapping will only occur if the cursor is positioned within the maximum snap distance from a vertex. When the cursor is further away from any vertex than the maximum snap distance then WinTopo Pro uses whichever of Snap to Pixel Centre or Snap to Vertex is currently depressed.

Snap to Polyline End Snap to Polyline End
This mode causes digitised points to snap onto the end points of polylines on the drawing.

This is useful for forming closed polygons, and linking one polyline to the end of another.

The Snap to Polyline End mode is affected by the Maximum Snap Distance setting in the Digitising Options. So snapping will only occur if the cursor is positioned within the maximum snap distance from a polyline end point. When the cursor is further away from any polyline end point than the maximum snap distance then WinTopo Pro uses whichever of Snap to Pixel Centre or Snap to Vertex is currently depressed.


Related Topics: