This option imports point coordinate data from files of various formats and enters the points into the current job database. The option may be used to transfer point data into Geoida from either external sources, or from one Geoida job to another using the Geoida INT (internal) file format (refer to List Points / Export option). In addition, if the source data is of a different datum or coordinate system from that defined for the current job, a transformation may be applied to the data.

IMPORTANT - DO NOT import data that is not compatible with the current job's configuration settings as defined by Job Configuration. Geoida INT files include several header lines of job detail information - these should first be checked against the current job's configuration to verify particularly that the spheroid and datum settings are the same. If importing data files of third party origin, check spheroid and datum details with the supplier and compare with the current job configuration - if datum or spheroid are different, apply a transformation.

The Import Points window is displayed when this option is selected.

Figure 1: Import Points option

More Info:

When Geoida is running, details of the purpose and use of each control in this window will be displayed in the bottom panel when the mouse is passed over any active object.


Unless the format selected for the import source file is Geoida INT or one or two others of the Specific formats in which the horizontal and vertical datums of the source data may be defined in the file, the datums for the incoming data will otherwise be assumed to be the same as that already defined for the job - see IMPORTANT note above. In some cases the zone number for grid coordinates and the geoid-spheroid separation may not be defined in the data file so the defaults as entered in the Zone and G-S Sep fields will be applied. If a transformation is specified, the default zone number and geoid-spheroid separation (if applicable) are applied to the incoming data before transformation if not defined within the incoming data.

Geoida Internal format (INT)

If it is necessary to edit a Geoida internal transfer file before importing, care should be taken to avoid disturbing the header format. Geoida skips over the initial header lines but examines the file to locate the column headers from which it determines the coordinate type. Data is expected to be found in pre-defined columns and errors may result if the column format is changed. Coordinates will be converted into the required type for the job - for example, if the job is set as 'Grid Projection', latitude and longitude values read from the file will be converted to the equivalent easting and northing values for the current spheroid and projection.

Format types

The imported file may be either of a simple generalised text format (General option) or in a specific named format (Specific option):

Select the required format type (General or Specific) and choose the format from the drop-down list - if the file format is selected before selecting the actual file, on clicking the Select button the file specification in the Open File dialog will be pre-set to the required file type; in some cases, if a file is subsequently selected not having an extension in keeping with the previously selected format, the format selection may change to a more compatible type. The format required may also be defined in the first instance by selecting in the Open File dialog and the format selection in the General - Specific drop-down list will be changed accordingly.

The View Log button in the Import Points window is normally disabled, but after loading the file or if the data is transformed, the button will become enabled so that the log file may be examined. Details of the importation (and transformation, if any) and any errors encountered during the import operation will be shown in the log file.

AutoCAD DXF (ASCII) format

For reading files in DXF format, the default setting is with the Read Points from Lines & Polylines checkbox un-checked whence points will be read only from the POINT entities section. However, if additional points are required to be read from LINE entity end-points or POLYLINE vertices, check the box. Because POINT entities are defined first in a DXF file, any of these additional points may actually duplicate those already loaded - Geoida therefore checks for points with the same coordinates and omits any duplicates.

Testing of coordinate values

Except for jobs configured for Plane coordinates (refer to Job Configuration option), all points read from file for importation are tested, either immediately as read or after transformation, to ensure that acceptable ranges are not violated with respect to the type of data, absolute values and the job datum. Geographic coordinates must be within the ranges +/- 90 degrees latitude and +/- 180 degrees longitude. For a standard Transverse Mercator grid projection, coordinates must be positive and less than 10 million metres; for special-area Transverse Mercator project grids or other types of projections, the limits are defined by the projection's Grid Extents (refer to the Projection option) and permitted to be ΒΌ of the zone's width or length outside these limits. Points that do not conform to acceptable ranges are omitted; if the number of failed points reaches 100 the following warning is displayed to permit the user to abandon the import if desired:

The number of points with coordinates out-of-range now exceeds 100
Do you wish to continue importing ?

Failure to load points will be noted in the log file, and a concluding message will be displayed such as

114 points falling out-of-range were omitted - refer to log file for details

A 'Zone warning' may also be printed in the log file if a transformation has been applied and the coordinates of the new point tested either outside the target zone or still within the original zone. This applies particularly to Zone-to-Zone, Grid-file and 3D-Similarity transformations because each of these requires that the original coordinates be first converted (if necessary) to geographic coords which are tested against the zone boundaries.

Coordinate conversion and precision

The coordinates of imported points will be converted to the coordinate system as set for the job, even if a transformation is performed on the incoming data; i.e. if the Coordinate System for the job is defined in Job Configuration as Grid Projection, the imported points will be stored as grid even if they are defined in the imported file as geographic. The more accurate representation of point position in a geodetic reference system is by geographic coordinates (latitudes and longitudes); grid projection coordinates are only a derivative from geographic coordinates and position accuracy is lost in the conversion process to grid. If a transformation between different datums is made during importation, particular care should be taken as a number of grid-to-geographic, geographic-to-grid, and datum-to-datum conversions may be necessary, and with each step of the process some accuracy will be lost. Every opportunity should be observed to reduce the number of conversion steps required; working with geographic coordinates is the best means of reducing precision loss during conversions.

See Data Transformations - General under the General Transformation Principles heading and Loss of precision with repeated transformation sub-heading for more discussion.

Transformation during import

If a transformation of the incoming data is required, first cross the Transform check-box - this will enable the Select Transformation button and the Log Details check-box; in addition, the Load button's caption will be changed to display Transform.

Figure 2: Definition of a transformation during import

Clicking on the Select Transformation button will open the Select Transformation window where a compatible data transformation may be selected. The points to be imported must be of the same coordinate type as the Source coordinate type set in this window because no additional conversion between grid and geographic coordinate types can take place before transforming each point (as could be done in the List Points / Export or Transform Job options), since at the point of transformation in this case, the datum and projection details of the source are not known. The only details known about the transformation before actually transforming each point are for the job and these details will not be the same as for the source system.

Hence, the 'Source' and 'Target' coordinates systems are defined as follows:

IMPORTANT - ALWAYS verify the accuracy and reliability of a transformation before applying to critical data - always test first with points whose coordinates are known in both systems.

Refer to the Transform Job option for details of the Select Transformation window, and to the Definitions menu Transformations option and the Data Transformations - General topic for additional information.

Transforming import file

Transformation of the imported source file is available for a small number of 'Specific' formats where the imported file is duplicated but with all coordinates re-written as transformed values matching the current job datum.

Figure 3: Transformation of an imported file

This option appears as the Transform imported file checkbox which is visible only when a suitable Specific format type is selected. The checkbox is enabled (i.e., the option may be used if required) only in the following circumstances:

Note that points imported into the job may be re-numbered if required but if the import file contains point numbers or alpha-numeric IDs, the original point numbers or IDs are not changed in the transformed file. With the exception of lines containing coordinate values, all other data contained in the file will remain unchanged.

Note also that heights are required for a Molodensky or 3D-Similarity transformation. Since some types of record in the imported file may contain only horizontal coordinate values and no height value (eg TEXT and POLYGON records in a Civilcad AS5 file), a temporary height of zero is assigned to prevent the transformation failing so that all coordinates in the file are transformed and a complete file is produced. However this may result in very slight errors in the transformed horizontal values for these entities - refer to Multi-Parameter Transformation under the heading Point Heights for further details.

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