📌 Snap Function Overview
This function allows you to snap to an OS feature or an existing overlay graphic, creating a graphic that precisely matches the OS feature or overlay graphic.
⚙️ General Snapping Information
To snap to an OS feature or overlay graphic:
Select the ➕ Add menu option and choose the overlay graphic type you want to add (Polyline, Polygon, Symbol, etc.), or
Select ✏️ Edit > Foreground Overlay > Edit Graphics to modify an existing graphic.
During the process of editing or adding geometry, dialog boxes will appear. These options can be selected using:
🖱️Mouse clicks, or
⌨️ Keyboard shortcuts (underlined letters on the dialog box or via the main status bar).
See The GGP Environment for details on the main status bar.
🖱️ Using Snap
When the desired graphic type is selected, position the cursor over the OS feature or overlay graphic.
Press F2 or right-click to display the snap menu.
Click Snap.
The selected OS feature or overlay graphic will be highlighted, and a dialog box will appear in the top-left corner of your screen.
You can select options using the 🖱️ Mouse or ⌨️ Keyboard shortcuts.
🛠 Snap Options
🔹Part Line
The Part Line option provides the option to snap to a point, a section, or the whole of the highlighted feature.
If the other end of the feature is outside the current view, the current view will be automatically centred on the endpoint of the feature.
Note: This feature is not available while snapping to create a symbol.
📏 Include All of Line/Polygon
This option is available if snapping to the beginning of an entire OS feature or an existing overlay polyline/polygon graphic.
Not available in snap to create a symbol.
If you find that you have snapped to a midpoint of the feature and that you could have selected the beginning point then press [Escape] and reselect the beginning point.
↩ Include All the Line in Reverse
Use this option to snap to a line feature and then continue from the point you just snapped to.
📐 Calculate from Snap Point / Calculate from Start of Line
If this option is checked the dialog box changes to provide three further options.
If you select Calculate from start of line then the initial point used for measuring the length will be the beginning of the snapped feature (i.e., the first node found).
Note: These options are not available for objects such as circles, rectangles, or symbols.
If GGP has selected the wrong end of the line then you will be presented with an option to change to the other end.
📏 Length
If you specify this option without entering an offset then you will be presented with a line that begins with the snap point you specified and is the length you specified.
If you select Calculate from start of line then the first point will be the start of the line.
If GGP determines that the line could travel in both directions along the line you will be asked to confirm which direction you want.
If the length you have specified is too long for the feature you are snapping to then you will be presented with a "Line truncated to..." message.
📐 Offset
If you enter an offset then you will be presented with a snap point rather than a whole line.
The offset will be perpendicular to the line at the length from the snap point specified.
When snapping in a clockwise direction a positive offset will be to the right.
To specify an offset in the other direction, enter a negative offset.
📏 Guide Line
If you check this box then a guide line will be drawn perpendicular to the line you are snapping to and at the length specified.
You can reverse the direction if the length is being measured in the wrong direction.
The line will be infinitely long.
You can select a point along the line by left-clicking along it.
If the point you have selected is within the search tolerance of another feature then a dialog will be shown to determine the precise snap point you require.
Nearest point to projected line will calculate the point exactly where you have selected it.
If you select Intersection point with feature then features within search tolerance will be highlighted.
You can change between features by selecting the [Previous...] or [Next...] buttons.
The currently selected feature will be highlighted.
If you select [OK] then the intersection between the guide line and the selected feature will be used as the snap point.
✦ Next Feature
If the feature highlighted on screen (after selecting snap) is the wrong feature, clicking this button changes the current highlight to the neighbouring feature.
✦ Previous Feature
If the Next feature button has been pressed to highlight a feature other than the originally highlighted feature, clicking this button steps back through the highlighted features.
✦ Next Overlay
If the feature in the overlay highlighted on screen (after selecting snap) is the wrong feature in the wrong overlay, clicking this button changes the current highlight to a neighbouring feature in the next overlay.
✦ Previous Overlay
If the Next Overlay button has been pressed to highlight a feature in another overlay, clicking this button steps back through the highlighted features in the previous overlay files.
🔄 Navigation Buttons in Snap Dialog
➡ Next Feature: Moves highlight to the next feature.
⬅ Previous Feature: Moves highlight to the previous feature.
➡ Next Overlay: Moves highlight to the next overlay feature.
⬅ Previous Overlay: Moves highlight to the previous overlay feature.
If offsetting from the beginning of a line, snapping to the same line again retains the “Calculate from start of line” and “Snap to Guideline” states.
🏗 Practical Use
The chainage & offset feature allows you to input measurements along a road centerline and offset them for accurate placement of real-world data.
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