Auto-Pick settings are found in the Configuration menu, on the Coordinate Reference System tab, in Geodetic Settings as "Use Auto-Pick for coordinate transformations".
Within the Geodetic Settings, available from the Coordinate Reference System tab of the Configuration menu, the option to Use Auto-Pick for coordinate transformations speeds up the process of choosing a new coordinate system. Unless a specific transformation is needed, checking this box can save time and make Global Mapper do the work of choosing the best way to go between different systems.
When Auto-Pick is enabled, grid files needed for transformations may be downloaded automatically. When this occurs, a "Grid file download progress" bar will be shown.
There are two possible behaviors for this setting:
Use most accurate GeoCalc selection(s)
If selected, Global Mapper will choose the most accurate transformation available without prompting for additional user input. First, it will filter transformations based on broad criteria, then pick the best available. This ensures that a relevant, high-accuracy transformation is chosen. This option is selected by default.
General Priorities:
When Auto-Picking a transformation, Global Mapper prioritizes transformations with a matching Area of Use for the loaded data, and then it prefers direct shifts over indirect shifts with multiple steps. This leads to the following priorities for overall category of transformation:
- Direct shift with a matching Area of Use
- Indirect shift (multiple steps via an intermediate) with a matching Area of Use
- Direct shift without a matching Area of Use
- Indirect shift (multiple steps via an intermediate) without a matching Area of Use
Specific Priorities:
If multiple transformations are available within the same "tier" of priority above, then one will be chosen based on the following priority tiers:
- If the Area of Use is matched, priority will be given to high-accuracy grid-based transformations, such as NTV1, NTV2, ED50 to ED87 North Sea, NADCON, NADCON5, NTF to RGF93, Ordnance Survey Grid, and Tokyo to JGD2000
- If none of those are available, or if Area of Use is not matched, next priority is given to 10-Parameter Molodensky Badeskas transformations
- 7-Parameter CFR and 7-Parameter PVR transformations
- 6-Parameter, 3-Parameter Molodensky, 4-Parameter, Geocentric Translation, Longitude Rotation
- Anything else
If there are multiple transformations within the same "tier" of priority, then the one with the best accuracy value is chosen.
Additionally, if none of the above succeeds, Global Mapper will check if both datums are considered WGS84 equivalent. If they are, then it will report that no transformation is needed.
Attempt to match legacy Global Mapper selections
If selected, when choosing a new coordinate system, data will be transformed and/or reprojected in the same way as in versions of Global Mapper before v27. In some cases, this may cause Global Mapper to use a transformation that is less accurate, but can help to ensure consistency when using workspaces saved in earlier versions.
Geodetic Settings that affect Auto-Pick behavior:
If Filter coordinate transformations by area of use is unchecked, then Area of Use will not be considered when auto-picking transformations.
If Allow Null Transformations is unchecked, Auto-Pick will also not be able to select “None”, with the exception of when an unknown vertical coordinate system is in use.
If Show deprecated geodetic definitions is checked, then they will be considered only once all other options have been exhausted. If the setting is unchecked, they will not be considered by Auto-Pick at all.
If Enable 'via intermediate' category is unchecked, then indirect shifts will not be considered.