org.geotools.mbstyle.parse

Class MBFunction

Object

MBFunction

public class MBFunction
extends Object

MBFunction json wrapper, allowing conversion to a GeoTools Expression.

Each function is evaluated according type: MBFunction.FunctionType.IDENTITY, MBFunction.FunctionType.INTERVAL, MBFunction.FunctionType.CATEGORICAL, MBFunction.FunctionType.EXPONENTIAL.

We have several methods that intelligently review getType() and produce the correct expression:

• color()
• numeric()
• function(Class)
• enumeration(Class)

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	MBFunction.FunctionCategory Function category property, zoom, or property and zoom.
static class	MBFunction.FunctionType Optional type, one of identity, exponential, interval, categorical.

Field Summary

Fields

Modifier and Type	Field and Description
protected JSONObject	json
protected MBObjectParser	parse

Constructor Summary

Constructors

Constructor and Description
MBFunction(JSONObject json)
MBFunction(MBObjectParser parse, JSONObject json)

Method Summary

Modifier and Type	Method and Description
EnumSet<MBFunction.FunctionCategory>	category() Programmatically look at the structure of the function and determine if it is a Zoom function, Property function or Zoom-and-property functions.
Expression	color() GeoTools Expression from json definition that evaluates to a color, used for properties such as 'color' and 'fill-color'.
static MBFunction	create(JSONObject json) Function as defined by json.
Expression	enumeration(Class<? extends Enum<?>> enumeration) GeoTools Expression from json definition that evaluates to the provided Enum, used for properties such as 'line-cap' and 'text-transform'.
Expression	font() GeoTools Expression from json definition that evaluates to a font string, used for 'text-font'.
Expression	function(Class<?> clazz) GeoTools Expression from json definition.
Number	getBase() (Optional) Number.
Object	getDefault() A value to serve as a fallback function result when a value isn't otherwise available.
String	getProperty() If specified, the function will take the specified feature property as an input.
JSONArray	getStops() Functions are defined in terms of input and output values.
MBFunction.FunctionType	getType() Access the function 'type', or null if not specified.
MBFunction.FunctionType	getTypeWithDefault(Class<?> clazz) Return the function type, falling back to the default function type for the provided Class if no function type is explicitly declared.
boolean	isArrayFunction() Returns true if this function's stop values are all arrays.
Expression	numeric() GeoTools Expression from json definition that evaluates to a numeric, used for properties such as 'line-width' and 'opacity'.
List<MBFunction>	splitArrayFunction() Splits an array function into multiple functions, one for each dimension in the function's stop value arrays.

Methods inherited from class Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

parse

protected final MBObjectParser parse

json

protected final JSONObject json

Constructor Detail

MBFunction

public MBFunction(JSONObject json)

MBFunction

public MBFunction(MBObjectParser parse,
                  JSONObject json)

Method Detail

getType

public MBFunction.FunctionType getType()

Access the function 'type', or null if not specified.

Depending on the domain you are working with ( enumeration(Class), color(), enumeration(Class)} ) the default value to use is different. These functions check for null and use the appropriate setting.

Returns:

function type, or null if not defined.

getDefault

public Object getDefault()

A value to serve as a fallback function result when a value isn't otherwise available. It is used in the following circumstances:

• In categorical functions, when the feature value does not match any of the stop domain values.
• In property and zoom-and-property functions, when a feature does not contain a value for the specified property.
• In identity functions, when the feature value is not valid for the style property (for example, if the function is being used for a circle-color property but the feature property value is not a string or not a valid color).
• In interval or exponential property and zoom-and-property functions, when the feature value is not numeric.

If no default is provided, the style property's default is used in these circumstances.

Returns:

The function's default value, or null if none was provided.

getTypeWithDefault

public MBFunction.FunctionType getTypeWithDefault(Class<?> clazz)

Return the function type, falling back to the default function type for the provided Class if no function type is explicitly declared. The parameter is necessary because different output classes will have different default function types.

Examples (For a function with no explicitly declared type):

 getTypeWithDefault(String.class); // "interval" function type
 getTypeWithDefault(Number.class); // "exponential" function type
 

Parameters:

clazz - The class for which to return the default function type

Returns:

The function type, falling back to the default when the provided Class is the return type.

See Also:

The "type" header under Mapbox Spec: Functions

getProperty

public String getProperty()

If specified, the function will take the specified feature property as an input. See Zoom Functions and Property Functions for more information.

Returns:

property evaluated by function, optional (may be null for zoom functions).

category

public EnumSet<MBFunction.FunctionCategory> category()

Programmatically look at the structure of the function and determine if it is a Zoom function, Property function or Zoom-and-property functions.

Returns:

Classify function as MBFunction.FunctionCategory.PROPERTY, MBFunction.FunctionCategory.ZOOM or both.

getStops

public JSONArray getStops()

Functions are defined in terms of input and output values. A set of one input value and one output value is known as a "stop."

Returns:

stops definition, optional may be null.

getBase

public Number getBase()

(Optional) Number. Default is 1. The exponential base of the interpolation curve. It controls the rate at which the function output increases. Higher values make the output increase more towards the high end of the range. With values close to 1 the output increases linearly.

Returns:

The exponential base of the interpolation curve.

create

public static MBFunction create(JSONObject json)

Function as defined by json.

The value for any layout or paint property may be specified as a function. Functions allow you to make the appearance of a map feature change with the current zoom level and/or the feature's properties.

Parameters:

json - Definition of Function

Returns:

Function as defined by json

color

public Expression color()

GeoTools Expression from json definition that evaluates to a color, used for properties such as 'color' and 'fill-color'.

This is the same as numeric() except we can make some assumptions about the values (converting hex to color, looking up color names).

• MBFunction.FunctionType.IDENTITY: input is directly converted to a color, providing a way to process attribute data into colors.
• MBFunction.FunctionType.CATEGORICAL: selects stop equal to input value
• MBFunction.FunctionType.INTERVAL: selects stop less than numeric input value
• MBFunction.FunctionType.EXPONENTIAL: interpolates an output color between two stops

If type is unspecified exponential is used as a default.

Returns:

Function (or identity Expression for the provided json)

font

public Expression font()

GeoTools Expression from json definition that evaluates to a font string, used for 'text-font'.

Fonts only use interval functions

• MBFunction.FunctionType.INTERVAL: selects stop less than numeric input, and returns stop value as a number

Returns:

Expression providing font string (used for `text-font`)

numeric

public Expression numeric()

GeoTools Expression from json definition that evaluates to a numeric, used for properties such as 'line-width' and 'opacity'.

This is the same as color() except we can make some assumptions about the values (converting "50%" to 0.5).

• MBFunction.FunctionType.IDENTITY: input is directly converted to a numeric output
• MBFunction.FunctionType.CATEGORICAL: selects stop equal to input, and returns stop value as a number
• MBFunction.FunctionType.INTERVAL: selects stop less than numeric input, and returns stop value as a number
• MBFunction.FunctionType.EXPONENTIAL: interpolates a numeric output between two stops

If type is unspecified exponential is used as a default.

Returns:

Function (or identity Expression for the provided json)

function

public Expression function(Class<?> clazz)

GeoTools Expression from json definition.

Delegates handling of Color, Number and Enum - for generic values (such as String) the following are available:

• MBFunction.FunctionType.IDENTITY: input is directly converted to a literal
• MBFunction.FunctionType.CATEGORICAL: selects stop equal to input, and returns stop value as a literal
• MBFunction.FunctionType.INTERVAL: selects stop less than numeric input, and returns stop value a literal

If type is unspecified interval is used as a default.

Parameters:

clazz - Type of data expected

Returns:

Function (or identity Expression for the provided json)

enumeration

public Expression enumeration(Class<? extends Enum<?>> enumeration)

GeoTools Expression from json definition that evaluates to the provided Enum, used for properties such as 'line-cap' and 'text-transform'.

• MBFunction.FunctionType.IDENTITY: input is directly converted to an appropriate literal
• MBFunction.FunctionType.CATEGORICAL: selects stop equal to input, and returns stop value as a literal
• MBFunction.FunctionType.INTERVAL: selects stop less than numeric input, and returns stop value a literal

If type is unspecified internval is used as a default.

Returns:

Function (or identity Expression for the provided json)

isArrayFunction

public boolean isArrayFunction()

Returns true if this function's stop values are all arrays.

For example, the following is an array function:

 "{'property':'temperature',
   'type':'exponential',
   'base':1.5,
   'stops': [
          // [stopkey, stopValueArray]
             [0,       [0,10]],
             [100,     [2,15]]
    ]
   }"
 

Returns:

true if this function's stop values are all arrays.

splitArrayFunction

public List<MBFunction> splitArrayFunction()
                                    throws ParseException

Splits an array function into multiple functions, one for each dimension in the function's stop value arrays.

For example, for the following array function:

 "{'property':'temperature',
   'type':'exponential',
   'base':1.5,
   'stops': [
          // [stopkey, stopValueArray]
             [0,       [0,10]],
             [100,     [2,15]]
    ]
   }"
 

This method would split the above function into the following two functions:

"X" Function:

 "{'property':'temperature',
   'type':'exponential',
   'base':1.5,
   'stops': [
          [0,   0],
          [100, 2]
    ]
   }"
 

And "Y" Function:

 "{'property':'temperature',
   'type':'exponential',
   'base':1.5,
   'stops': [
          [0,   10],
          [100, 15]
    ]
   }"
 

Returns:

A list of MBFunction, one for each dimension in the stop value array.

Throws:

ParseException