ShiftWiz from Dotted Eyes

ShiftWiz automatically shifts map features in your own layers of asset data by warping them to fit a set of control vectors, as if the layer was on a rubber sheet.

This is required in cases where features have been digitised to fit a set of base maps, and the base maps are later adjusted as a result of a more accurate survey.

Ordnance Survey PAI Programme

Ordnance Survey carried out just such a survey and published a national programme of positional accuracy improvement to the Land-Line and OS MasterMap products for rural areas mapped at 1:2,500 scale. The implementation started in June 2001 and is now complete; however, you may be like many organisations that due to operational reasons have yet to address the impact on your asset data.

ShiftWiz adds value to PAI

ShiftWiz goes beyond the essential rubber-sheeting process. It can optionally ‘snap’ each of the vertices in your own layer to the nearest vertex in a reference layer, such as the new base map – you can even specify a distance tolerance to search within.

ShiftWiz processes a complete layer at a time. It creates a new output file, containing the same features - shifted in position according to the control vectors.

The control vectors required by ShiftWiz are defined as coordinate records, each with a feature code, in a file of Comma-Separated Values (CSV). This is the same format used by Ordnance Survey to record positional shifts in Land-Line or DNF base maps as a result of the positional accuracy improvement programme. These files record the original location of selected points on the original base map and their new location after positional accuracy improvement.

Benefits

• Apply the weighted effect of control vectors to all features in your own layers;
• Copy all attribute data automatically from the original features to the shifted features;
• Use the CSV files supplied by Ordnance Survey, or alternatively create your own;
• Process different types of feature at the same time - points, lines, regions and text features;
• Specify either all control vectors, or only those relating to, say, buildings;
• Trade off the precision of local shifts at the control points against any distortions in shape;
• Control how the shifting effect tapers off and is constrained outside the area of control vectors;
• Edit the layer containing shift vectors using your own GIS software (to eliminate rogue vectors);
• Snap each of the vertices in your own layer to the nearest vertex in a reference layer such as a new base map.

Next steps

Talk to a Dotted Eyes' consultant about how we can help you with your PAI project by calling 01527 556920 or send email us.

Visit Ordnance Survey's website for more information about Ordnance Survey’s Positional Accuracy Improvement Programme.