GeoConcept Map Writer Parameters

Specifies the pathname to the map file that will be used as a template for the destination map. The precision, extents, and any layer information from the template map will be preserved, but class definitions will not.

Since the template map sets the precision of the coordinates, it is important to select a template map with an appropriate precision. There are two possible problems to guard against. The first is when the precision is too low, and the geometry of lines and polygons is affected by this lack of precision. For example, given a line with points at coordinates (1.001, 4.002) and (1.05, 4.082), but a precision of only .1 will result in a map with a line-type object, but whose coordinates are (1.0, 4.0) and (1.0, 4.0); i.e. the same point! In particular, polygons can suddenly change shape radically, or lose all area if they contain points that differ by a value smaller than the precision of the map.

The other problem that you should guard against is setting the precision too high. GeoConcept maps store all coordinates as integers, multiplying coordinates by powers of ten in order to retain the fractional elements of coordinates. For example, a coordinate of 445533.023, when stored in a map with precision of 0.0001, will store this coordinate as the integer 4,455,330,230. On a 32-bit machine, the maximum value for an integer is 2,147,483,647. It is thus easy to see that with extremely high precision maps, it is possible for coordinates at the high end of the ranges of latitudes and longitudes can be greater than this value. If this occurs, the translation will fail, and the log file will indicate that the precision of the map is too high for the given coordinates.

The value of this parameter determines whether the constructed subclass is 2D or 3D. If set to Auto Detect (the default), the subclass will be determined by the geometry of the first feature read.

In GeoConcept, a subclass is either 2D, 3D, or 3D Mono. The latter is used only for lines and polygons, and it means a 3D line or polygon in which the entire geometry is at some specific height/altitude.

A 3D Mono geometry takes the Z-value from the first coordinate and stores the rest of the coordinates as 2D with the understanding that they are really 3D with the same Z-value as the first coordinate. It is impossible to write a 3D geometry to a 2D subclass, where the Z-value is retained. However, it is possible to write a 2D geometry to a 3D subclass (where the Z-value is undefined).

When a Template map is selected, it is used to determine extents and resolution of the map. This parameter controls whether the class/subclass structure of the map and all the objects in it should be deleted.

If the default value Class_Definitions is used, then the destination map is entirely emptied out of any class and subclass definitions. What will remain in the map is the extents, resolution, and any defined global fields.

By setting this parameter to Nothing, the destination map is left as a copy of the template; therefore, the writer will insert data directly into (a copy of) an existing GeoConcept map.

This required parameter controls the strings that will be used for the creation of the class and subclass definitions in the output GeoConcept map. If it is set, the format attributes gcm_class_name and gcm_subclass_name will be used for the GeoConcept class and subclass definitions, respectively.

In a GeoConcept-to-GeoConcept translation, this will be set to Yes by default.

For translations that are not GeoConcept-to-GeoConcept, this parameter can be set to Yes, but the format attributes gcm_class_name and gcm_subclass_name must be exposed on the destination feature type definitions, and appropriate values be assigned. It is imperative that each feature type receive a combination of class and subclass values (via the format attributes) that is unique.

For example, setting these attributes to the same value for both a feature type that only supports polygon geometry, and a feature type that only supports point geometry will result in a failed translation, since each combination of class and subclass supports only a single geometry type. Even if the geometries of two feature types agree in value, if their attributes are different, the result can be a loss of data, since only the first feature type definitions attribute values will be accepted.