Calculate Attributes

Calculates a new or overwrites an existing attribute.

Parameter

Name	Type	Description
attribute	STRING	view_name.attribute_name
attributeType	STRING	INT, DOUBLE, STRING, DOUBLEVECTOR
variables	STRING_MAP	variable name; view_name.attribute_name or view_name.linked_view_name.attribute_name to resolve the links view_name.linked_view_name_id needs to exist
equation	STRING	equation to solve e.g. variable_a + 5 attributes used in equation need to be defined as variables

Data-stream

View	Attribute	Type	Access	Description
attribute view		COMPONENT	read
	attribute	any	write
variable view		COMPONENT	read
	attribute_name	any	read
	linked_view_id	INT	read	(if linked attribute)
linked view		COMPONENT	read
	attribute_name	any	read

Detailed Description

The module integrates the muparser library, a parser for mathematical equations and can access variables of linked components.

Common use cases

Assign a constant

attribute:     building.construction_year
attributeType: INT
variables:
    (empty)
equation:      1990

Assign a constant from global object

attribute:      building.construction_year
attributeType:  INT
variables:
     y : city.year
equation:       y

Note

When non - linked variables are defined the attribute of the first found feature is returned. Therefore only use in combination where it is guaranteed that only one feature exists within a view. (e.g. city or world)

Assign only to a subset

attribute:        building.construction_year
attributeType:    INT
variables:
     y : city.year
     c : building.construction_year # Variables might have the be initialed before they can be overwritten. This can be done by assigning a constant
equation:         y == 0 ? y : c # If year is not defined (0) the year is set to city.year, otherwise building.construction_year is assigned

Note

For this use case setting a module filter is much more efficient. Use the Assign constant example and set the module attribute filter to building: construction_year is null

Calculate Number of people in a city district

attribute:         district.population
attributeType:     INT
variables:
    pop : district.parcel.building.household.persons
equation:          pop # Assigns the number of people living in a district. The data is derived from the linked feature.

Note

Links are resolved through a recursion and the sum of all the connected attributes is returned.

Increase increment in loop

attribute:          city.year
attributeType:      INT
variables:
     y : city.year # Variables might have the be initialed before they can be overwritten. This can be done by assigning a constant
equation: y + 1

Further to the expression provided by the muparser library following expressions are supported:

Expressions

Name	Description
rand(value)	returns random number in range ]0-value]
round(value)	rounds value to nearest int value
counter	current counter when used in loops
int(value)	convert float to int
num2str(value)	number to string
str2num(value)	string to number
vecsum(array)	sum of a vector
vectimes(array,array)	multiply vectors element by element
? then : else	if clause e.g. a > 5 ? variable_a : variable_b see for the operators see
{1,2,3}	creates a vector. Note that this can only be used stand alone and not in combination any other expression
‘string a’ // ‘string b’	combine strings

Module Name

GDALAttributeCalculator