Filter Controls

Filter Controls can be used as a selection tool when using XSL Style Sheets to create reports or export data from LISCAD.

There are three kinds of Filter Controls:

• Point Filter
• Line Filter
• Polygon Filter

All the filter controls are basically identical in functionality. The only difference being in the type of attributes that can be selected depending upon the object type being filtered. The examples used in this discussion focus on the Point Filter Control, although the concepts apply equally to all filter controls.

Filter controls can be applied to objects within the database to extract only those objects containing certain attributes.

Points can be filtered using combinations of the following attributes:

• Code
• Description
• East
• North
• Elevation
• Enabled?
• Has Elevation?
• Identifier
• Group
• Is Contourable?

Lines can be filtered using combinations of the following attributes:

• Code
• Description
• Enabled?
• Group
• Is Arc?
• Is Boundary?
• Is Breakline?
• Is Circle?
• Is Line?
• Is Offset?
• Is Radiation?
• Is Spiral?
• Is Splay?
• Is Spline?
• Length
• Number

Polygons can be filtered using combinations of the following attributes:

• Area
• Code
• Description
• Group
• Number

The Filter Control allows the user to define a set of criteria based upon the above attributes and any object that satisfies the criteria will be selected for the output. Objects that don't satisfy the criteria will be filtered out.

To set up the criteria, based upon the above attributes, the Filter Control allows the user to define how the attributes should be compared with some bounding value or values. The user can select the Operator for an attribute comparison from within the Filter Control. Possible Operators are

• Less Than or Equal To (<=)
• Greater Than or Equal To (>=)
• Equals (=)
• Between
• Contains
• Does Not Contain
• Not Equal
• True
• False

Depending upon the chosen attribute, some of these options will be available in the Filter Control Operator list. For example, attributes which are inherently numbers or characters will have all operators except True or False available. The attributes 'Has Elevation?' and 'Is Contourable?' have only the True or False operators available.

The Filter Control allows the user to provide a value or values to compare the attribute against, based upon the comparison operator. Only one value is available for all Operators except 'Between', where two values need to be provided.

Using a combination of an Attribute, an Operator and a Value, the user can define criteria for a selection and a set of Criteria can be combined together to form a Test.

For example, if the Attribute "East" was chosen, with the Operator >=, and the Value of 300000, then the criteria would be defined as to test for all points with an Easting greater than or equal to 300000.

A Test will often consist of multiple criteria. Each criteria can be added to the test, which requires that every criteria is met. They are joined using a logical AND.

For example, if a criteria was added to the previous test, such that the new criteria was all points with a northing greater than 5800000, then all points with an easting greater than 300000 and northing greater than 5800000 would be chosen.

The AND join applies to all criteria in a test. Multiple tests can be included in a filter. The tests are joined using an OR. A test can be added by using the Add Test function.

Example:

Attribute	Operator	Bounding Value	Comment
Code	Equals	Pit	First Test
Description	Contains	Defect
OR
Group	Equals	Pole	Second Test
Description	Contains	Condemned

This filter will choose all the points with either a code 'pit', and also have 'defect' in their description (First Test) or are on group 'pole' and have 'condemned' in their description (Second Test)

Filters can be saved for use by a particular user. They can be used repeatedly in different projects.