NMEA AIS – Marine Navigation Data Reader Parameters

Using the minimum and maximum x and y parameters, define a bounding box that will be used to filter the input features. Only features that intersect with the bounding box are returned.

If all four coordinates of the search envelope are specified as 0, the search envelope will be disabled.

When selected, this parameter removes any portions of imported features being read that are outside the Search Envelope.

The example below illustrates the results of the Search Envelope when Clip to Search Envelope is not selected (set to No) and when it is selected (set to Yes).

• No: Any features that cross the search envelope boundary will be read, including the portion that lies outside of the boundary.
• Yes: Any features that cross the search envelope boundary will be clipped at the boundary, and only the portion that lies inside the boundary will be read. The underlying function for the Clip to Search Envelope function is an intersection; however, when Clip to Search Envelope is selected, a clipping operation is also performed in addition to the intersection.

In AIS, longer messages are split into multiple parts, which are related by an ID. However, the message IDs used when transmitting are not unique. This leads to the possibility that unrelated message pieces (if they have the same ID) could be combined. To prevent this, partially received multi-part messages are dropped as incomplete if the rest of the message is not found within the next set of incoming messages. The size of this set is determined by this parameter.

The value for this parameter is an integer. The default is 40.