Geoida Help

Interrogate Point

Select this option if you wish to view or edit details for individual points within the database.

The prompt Select required point appears in the status bar prompt-panel and a boxed-cross-hair pointer appears on the screen - place the pointer around the required point and click the mouse to select it for display. If a number of points fall within the cursor outline, the point closest to the centre will be selected.

If the required point cannot be picked from a concentrated group of points, use Zoom Point Range to exclude the persistent points that mask the point required, or use List Points / Export to select the point by point-number and use the Modify function.

The Interrogate Point window displays the point in the coordinate type according to the Coordinate System selection in Job Configuration which defines how points are stored in the database.

Convention for geographic coordinates

If point coordinates are displayed as geographic (latitudes and longitudes), the convention applied for entering or modifying the values (both here and otherwise throughout Geoida) is: south latitudes are -ve and north latitudes are +ve within the range -90 to +90 degrees; longitudes west of the Greenwich meridian (0 degrees) are -ve and east of Greenwich are +ve, range -180 to +180 degrees.

Geoid interpolation

The Interpolate button will normally be enabled if a geoid model exists unless the point is a fixed point, because it is expected that fixed points and their geoid-spheroid separation values will have been defined in the Enter Points option. If it is necessary to interpolate a new geoid-spheroid separation value for a fixed point from the model, un-cross the Fixed check-box which will then enable the Interpolate button, interpolate the new value, and then re-cross the Fixed check-box.

Define Alpha ID

As an alternative to using the Alpha-Numeric ID Cross-Reference option to define alpha point IDs and their point number cross-references, click the Define Alpha ID button to open the Alpha-Numeric Point ID Cross-Reference window and specify the alpha ID for the current point. Note that it is not necessary for every point to have an alpha ID - the field may be left blank if desired, but if there has already been an alpha ID defined in Alpha-Numeric ID Cross-Reference then it will be displayed here in the Alpha ID field.

Notes

1. If the selected point is displayed or edited in a coordinate type different from that in which it was originally stored (eg, it may have been stored as grid coordinates but it is currently being edited as geographic), slight changes to the coordinates may be made to the point if the OK button is clicked to close the window, even though no edit changes were specifically made by the user. This is because a coordinate conversion was made in order to display the coordinates in the alternative type, eg converted from grid to display latitude and longitude. Even though the number of decimal seconds displayed for geographic coordinates is 5, this is still only the equivalent of 3 decimal places of a metre for grid coordinates, and if a point was originally a calculated position (stored to double-precision accuracy) or was entered as grid coordinates accurate to 5 decimal places, this precision will be lost because the coordinates have been converted and the exact value as displayed will be saved after re-converting back to the original type. Therefore to preserve precision: (i) if possible, edit points only in their original coordinate type (usually will be the same as the job type), and (ii) avoid clicking the OK button to exit this window when no changes are made (use Cancel).
   
   
2. When the number of decimal places is increased (E,N or Height spin-buttons), the message Original values reloaded or Original height reloaded may appear. This is done to preserve (as much as possible) the precision of the point as already stored and to advised the user in case changes had already been made to the coordinates of the point before the decimal places was increased. Otherwise, if this was not done, the original precision of the stored point could be lost because it will be displayed at the default settings for the decimals and re-saved with the values truncated at those default decimal places.

Click OK to save or Cancel to discard any changes made to the selected point - the box-shaped cursor will re-appear to select another point as prompted. When Interrogate Point is no longer required, press the keyboard Escape button or the right mouse button to close the option; selecting another menu item will also terminate this option.

An alternative modify function is contained within the List Points / Export option, and new points can be created quickly by clicking their approximate positions on-screen and then editing the coordinates, with the Digitise Provisional Points option.