Norwegian Mapping Authority Extrapolation Point File¶
This page describes the format for extrapolation point files used in the Norwegian Mapping Authority's transformations.
File Format¶
Extrapolation point files contain coordinates for points in two coordinate systems. These points are used to calculate transformation parameters between the coordinate systems.
The format is as follows:
- First line: Header with coordinate system names and columns
- Following lines: Point names and coordinates
Example¶
EU89-UTM(Sone-32),NGO1048(Akse-3),P,N,E
PP2509 6628338.797 598488.690 198295.772 2032.237
PP2596 6628401.315 597866.501 198374.481 1411.718
PP3529 6628172.393 598409.881 198131.463 1949.122
PP3536 6628706.946 598040.826 198675.592 1593.939
Column Description¶
The format has the following columns:
- Point name: Identifier for the point (e.g., PP2509)
- N-coordinate in from-system: North coordinate in the source system (e.g., 6628338.797)
- E-coordinate in from-system: East coordinate in the source system (e.g., 598488.690)
- N-coordinate in to-system: North coordinate in the target system (e.g., 198295.772)
- E-coordinate in to-system: East coordinate in the target system (e.g., 2032.237)
Using Extrapolation Point Files¶
Extrapolation point files are used to improve transformations between coordinate systems. The points in these files serve as common reference points for the two systems and make it possible to calculate more accurate transformation parameters.
Accuracy and Point Placement¶
To achieve the best possible transformation, the extrapolation points should:
- Be evenly distributed over the area to be transformed
- Have high accuracy in both coordinate systems
- Include at least 3-4 points for basic transformation
- Ideally include 6-10 points for optimal accuracy
Note
The quality of the transformation depends heavily on the quality of the coordinates in the extrapolation point file. Therefore, always use well-documented and accurate coordinates.