# Use buffer expressions with GeoAnalytics Tools

The following tools in the GeoAnalytics Tools toolbox allow you to apply an expression:

The GeoAnalytics Tools that use expressions have different purposes, as well as limitations on the expressions that can be applied. At ArcGIS 10.6, all expressions used in GeoAnalytics support Arcade.

## Reconstruct Tracks and Create Buffers

Buffer expressions are used by the Reconstruct Tracks and Create Buffers tools.

Buffer sizes are commonly entered using constant or field values. However, entering values is not the only way you can specify a buffer size using GeoAnalytics Tools. In some cases, you may want to perform a mathematical calculation to set the buffer size. The calculation is applied to each analyzed feature. Calculations are performed when the analysis runs on your ArcGIS GeoAnalytics Server.

Buffer expression examples are included in the following sections.

## Mathematical operator and function examples

Buffer expressions mathematically process numbers. The following table shows a sample of available operations.

OperatorExplanationExampleResult

a + b

a plus b.

fieldname contains a value of 1.5.

\$feature["fieldname"] + 2.5

4.0

a - b

a minus b.

fieldname contains a value of 3.3.

\$feature["fieldname"]- 2.2

1.1

a * b

a times b.

fieldname contains a value of 2.0.

\$feature["fieldname"] * 2.2

4.4

a / b

a divided by b.

fieldname contains a value of 4.0.

\$feature["fieldname"] / 1.25

3.2

abs( a )

Returns the absolute (positive) value of a.

fieldname contains a value of -1.5.

abs(\$feature["fieldname"])

1.5

log( a )

Returns the natural logarithm (base E) of a.

fieldname contains a value of 1.

log(\$feature["fieldname"])

0

sin( a )

Returns the trigonometric sine of a. The input is assumed to be an angle in radians.

fieldname contains a value of 1.5707.

sin(\$feature["fieldname"])

1

cos( a )

Returns the trigonometric cosine of a. The input is assumed to be an angle in radians.

fieldname contains a value of 0.

cos(\$feature["fieldname"])

1

tan( a )

Returns the tangent of a. The input is assumed to be an angle in radians.

fieldname contains a value of 0.

tan(\$feature["fieldname"])

0

sqrt( a )

Returns the square root of a.

fieldname contains a value of 9.

sqrt(\$feature["fieldname"])

3

min( a, b )

Returns the lowest-valued number between a and b.

fieldname contains a value of 1.5 and a value of -3.

min(\$feature["fieldname"], -3)

-3

max( a, b )

Returns the highest-valued number between a and b.

fieldname1 contains a value of 1.5, and fieldname2 contains a value of -3.

max(\$feature["fieldname1"], \$feature["fieldname2"])

1.5

constrain(<value>,<low>,<high>)

Returns the input value if it's within the constraining bounds. If the input value is less than the low value, it returns the low value. If the input value is greater than the high value, it returns the high value.

constrain(\$feature["distance"], 0, 10)

constrain(\$feature['Store dist'], 6, distance)

Returns 0 if distance is less than 0, 10 if distance is greater than 10, and distance otherwise.

Returns 6 if Store dist is less than 6, distance if Store dist is greater than distance, and Store dist otherwise.

Multiplication example for a buffer expression

``\$feature["Distance"] * 2``

## As distance function examples

The as distance functions cast numeric values to a linear distance, which can then be used in a mathematical expression. The Reconstruct Tracks and Create Buffers tools can use as distance functions. If a numeric value is used without an as distance function, the unit is assumed to be meters.

FunctionExplanationExampleResult

as_meters( <value> )

Applies a calculation assuming the input values are in meters.

as_meters( \$feature["fieldname"] )

as_meters(150)

Results are buffered by 150 meters.

as_kilometers( <value> )

Applies a calculation assuming the input values are in kilometers.

as_kilometers( \$feature["fieldname"] )

as_kilometers(150)

Results are buffered by 150 kilometers.

as_feet( <value> )

Applies a calculation assuming the input values are in feet.

as_feet( \$feature["fieldname"] )

as_feet(150)

Results are buffered by 150 feet.

as_yards( <value> )

Applies a calculation assuming the input values are in yards.

as_yards( \$feature["fieldname"] )

as_yards(150)

Results are buffered by 150 yards.

as_nautical_miles( <value> )

Applies a calculation assuming the input values are in nautical miles.

as_nautical_miles( \$feature["fieldname"] )

as_nautical_miles(150)

Results are buffered by 150 nautical miles.

as_miles( <value> )

Applies a calculation assuming the input values are in miles.

as_miles( \$feature["fieldname"] )

as_miles(150)

Results are buffered by 150 miles.

For each feature, multiply the field Distance, assuming it's in kilometers, and add 10 meters for a buffer expression.

``as_kilometers(\$feature["Distance"]) * 3 + as_meters(10)``

## Conditional operators

Conditional statements can use the following operators:

OperatorExplanationExampleResults

a > b

a < b

a is greater than b

a is less than b

10 > 2

False

a >= b

a <= b

a is greater than or equal to b

a is less than or equal to b

abs(-10) >= 10

True

a != b

a is not equal to b

abs(-3) != -3

True

a == b

a is equal to b

abs(-5) == 5

True

<condition1> || <condition2>

Condition 1 or condition 2 is met.

(abs(-5) == 5) || (10 < 2)

True

<condition1> && <condition2>

Condition 1 and condition 2 are met.

(abs(-5) == 5) && (10 < 2)

False

Example of a buffer expression using advanced functions and conditions

``iff(field1 > field2, iff(field2 = 0, field3, field4), 0)``

Multiplication example for join condition

``iff(field1 > field2, iff(field2 = 0, field3, field4), 0) > \$join["Distance"] * 2``

## Logical operator examples

In addition to the conditional operators, more advanced logical operators can be used to create buffers as shown in the following table.

FunctionExplanationExampleResult

iif(<condition>,<true value>,<false value>)

Returns one value if a condition evaluates to true and returns another value if that condition evaluates to false.

<true value> and <false value> can be the following:

• A numeric field. If there is a space in the field name, use square brackets.
• A number.
• A function.

iif(\$feature["field1"] > \$feature["field2"], \$feature["field1"], 0)

iif(\$feature["field1"] > \$feature["field2"], iif(\$feature["field2"] = 0, \$feature["field3"], \$feature["field4"]), 0)

Returns field1 if field1 is greater than field2, and 0 otherwise.

Returns the result of the second iif function if field1 is greater than field2, and 0 otherwise.

when(<expression1> , <result1> , <expression2> , <result2> , ... , <expressionN> , <resultN>, <default>)

Evaluates a series of expressions in order until one evaluates to true.

• expression—An expression.
• result—The result of the expression. It can be a number or field.
• default—An optional value if none of the expressions match.

when((\$feature["field1"] + 10) > 1, 1,(\$feature["field2"] + 10) > 2 , 2, \$feature["field3"])

If field1 + 10 is greater than 1, returns 1. If not, checks if field2 + 10 is greater than 2. If yes, it returns 2. If not, it returns field3.

decode(<conditional val> , <case1> , <result1>, <case2>, <result2>, ... <caseN>, <resultN>, <defaultValue> )

Evaluates an expression and compares its value with subsequent parameters. If the expression matches, it returns the next parameter value. If none match, there is the option for the last parameter to be a default return value.

• conditional val—The conditional value. It can be a field or an expression.
• case—A value to be compared to the conditional val.
• result—The result if the corresponding case matches the conditional val.
• defaultValue—An optional value if no other values are true.

decode(\$feature["field1"] + 3 , \$feature["field1"], 1, \$feature["field2"], 2, 0)

Compares equality between the conditional val field1 + 3 and case1 field1. If true, it returns 1. If false, it compares the equality between field1 + 3 and field2. If true, it returns 2; otherwise, it returns 0.

## Track-aware examples

Reconstruct Tracks can use track-aware equations in Arcade as shown in the following table:

FunctionExplanationExampleResult

TrackStartTime()

Calculates the start time of a track in milliseconds from epoch.

Using a track that starts on January 2, 2017.

TrackStartTime()

1483315200000

TrackDuration()

Calculates the duration of a track in milliseconds from the start until the current time step.

Using a track that starts on January 2, 2017, and the current time is January 4, 2017.

TrackDuration()

172800000

TrackCurrentTime()

Calculates the current time in a track.

Using a feature that occurs on January 3, 2017, at 9:00 a.m.

TrackCurrentTime()

1483434000000

TrackIndex

Returns the time index of the feature being calculated.

Calculating this value on the first feature in a track.

TrackIndex

0

TrackFieldWindow(<fieldName>, <startIndex>, <endIndex>)

Returns an array of values in the given field for the specified time index. The window function allows you to go forward and backward in time. The expression is evaluated at each feature in the track.

• The current feature is at index 0.
• Positive values represent features that occur in the future, after the current value. For example, position 1 is the next value in the array.
• Negative numbers represent features that occurred in the past, before the previous feature. For example, -1 is the previous value in the array.

MyField has sequentially ordered values of [10, 20, 30, 40, 50]. The expression is evaluated at each feature in the track. Results are returned inclusive of the start feature, and exclusive of the end feature.

Example 1: TrackFieldWindow("MyField,-1,2)

Example 2: TrackFieldWindow("MyField,-2,0)

Example 3: TrackFieldWindow("MyField,0,3)

Example 1: When evaluated at each feature, the table shows the following results:

 Evaluated feature Result 10 [10,20] 20 [10, 20, 30] 30 [20,30,40] 40 [30,40,50] 50 [40, 50]

Example 2: When evaluated at index 2 (value is 30), it returns 10.

Example 3: When evaluated at index 2 (value is 30), it returns 50.

TrackGeometryWindow(<startIndex>, <endIndex>)

Returns an array of values representing geometry for the specified time index. The window function allows you to go forward and backward in time. The expression is evaluated at each feature in the track.

• The current feature is at index 0.
• Positive values represent features that occur in the future, after the current value. For example, position 1 is the next value in the array.
• Negative numbers represent features that occurred in the past, before the previous feature. For example, -1 is the previous value in the array.

MyField has sequentially ordered values of [10, 20, 30, 40, 50]. The geometry of the features is [{x: 1, y: 1},{x: 2, y: 2} ,{x: null, y: null},{x: 4, y: 4}, {x: 5, y: 5}]. The expression is evaluated at each feature in the track. Results are returned inclusive of the start feature, and exclusive of the end feature.

Example 1: TrackGeometryWindow(-1,2)

Example 2: TrackGeometryWindow(0,1) on a polyline dataset

Example 3: TrackGeometryWindow(0,1) on a polygon dataset

Example 4: Find the X value of the previous point TrackGeometryWindow(-1,0)["x"]

Example 1: When evaluated at each feature, the table shows the following results:

 Evaluated feature Result 10 [{x: 1, y: 1},{x: 2, y: 2}] 20 [{x: 1, y: 1},{x: 2, y: 2} ,{x: null, y: null}] 30 [{x: 2, y: 2} ,{x: null, y: null},{x: 4, y: 4}] 40 [{x: null, y: null},{x: 4, y: 4}, {x: 5, y: 5}] 50 [{x: 4, y: 4}, {x: 5, y: 5}]

Example 2: Polylines are returned in the following format: [{"paths":[[[-180,-22.88],[-177.6,-23.6]],[[180,-18.099999999999994],[179.7,-18.4],[179.4,-18.7],[178.9,-18.9],[178.5,-19.3],[178.2,-19.7],[178.4,-20],[178.8,-20.2],[178.9,-21.8],[179,-22.2],[179.4,-22.7],[180,-22.88]],[[-178,-17],[-178.8,-17.3],[-179.2,-17.5],[-179.6,-17.8],[-179.9,-18],[-180,-18.099999999999994]]]}]

Example 3: Polygons are returned in the following format: [{"rings":[[[-7882559.1197999995,6376090.883500002],[-7893142.474300001,6042715.216800004],[-8544018.775999999,6045361.0554000065],[-8544018.775999999,6376090.883500002],[-7882559.1197999995,6376090.883500002]]]}]

Example 4: Evaluated at index 2 (value is 30): 2

TrackWindow(<value1>, <value2>)

Returns an array of values representing geometry and all attributes for the specified time index. The window function allows you to go forward and backward in time.

• The current feature is at index 0.
• Positive values represent features that occur in the future, after the current value. For example, position 1 is the next value in the array.
• Negative numbers represent features that occurred in the past, before the previous feature. For example, -1 is the previous value in the array.

MyField has sequentially ordered values of [10, 20, 30, 40, 50], in addition to the objectID, globalID and instant_datetime fields. The geometry of the features is [{x: 1, y: 1},{x: 2, y: 2} ,{x: null, y: null},{x: 4, y: 4}, {x: 5, y: 5}]. The expression is evaluated at each feature in the track. Results are returned inclusive of the start feature, and exclusive of the end feature.

Example 1: TrackWindow(-1,0)

Example 2: geometry(TrackWindow(-1,0)["x"]

Example 1: When evaluated at each feature, the table shows the following results:

 Evaluated feature Result 10 20 [{"geometry": {x: 1, y: 1}},{"attributes": {"MyField" : 10, "trackName":"ExampleTrack1"}}] 30 [{"geometry": {x: 2, y: 2}},{"attributes": {"MyField" : 20, "trackName":"ExampleTrack1"}}] 40 [{"geometry": {x: null, y: null}},{"attributes": {"MyField" : 30, "trackName":"ExampleTrack1"}}] 50 [{"geometry": {x: 4, y: 4}},{"attributes": {"MyField" : 40, "trackName":"ExampleTrack1"}}]

Example 2: Evaluated at index 2 (value is 30): 2

Use the following track expressions to calculate distance, speed, and acceleration on tracks.

All distance calculations are calculated in meters, speed in meters per second, and acceleration in meters per second squared. Distances are measured using geodesic distances.

FunctionExplanation

TrackCurrentDistance()

The sum of the distances travelled between observations from the first to the current observation.

TrackDistanceAt(value)

The sum of the distances travelled between observations from the first to the current observation plus the given value.

TrackDistanceWindow(value1, value2)

The distances between the first (inclusive) to the last value (exclusive) in a window about the current observation (0).

TrackCurrentSpeed()

The speed between the previous observation and the current observation.

TrackSpeedAt(value1)

The speed at the observation relative to the current observation. For example, at value 2, it's the speed at the observation two observations after the current observation.

TrackSpeedWindow(value1, value2)

The speed values between the first (inclusive) and the last value (exclusive) in a window around the current observation (0).

TrackCurrentAcceleration()

The acceleration between the previous observation and the current observation.

TrackAccelerationAt(value1)

The acceleration at the observation relative to the current observation.

TrackAccelerationWindow(value1, value2)

The acceleration values between the first (inclusive) to the last value (exclusive) in a window around the current observation (0).

The example calculations for distance, speed, and acceleration will use examples from the following image: FunctionExample result

TrackCurrentDistance()

Point IDResult (meters)

P1

0

P2

60

P3

80 + 60 = 140

P4

30 + 80 + 60 = 170

P5

35 + 30 + 80 + 60 = 205

P6

25 + 35 + 30 + 80 + 60 = 230

TrackDistanceAt(2)

Point IDResult (meters)

P1

0 + 80 + 60 = 140

P2

30 + 80 + 60 = 170

P3

35 + 30 + 80 + 60 = 205

P4

25 + 35 + 30 + 80 + 60 = 230

P5

null

P6

null

TrackDistanceWindow(-1, 2)

Point IDResult (meters)

P1

[0,60]

P2

[0, 60, 140]

P3

[60, 140, 170]

P4

[140, 170, 205]

P5

[170, 205, 230]

P6

[205, 230]

TrackCurrentSpeed()

Point IDResult (meters/second)

P1

0

P2

60/60

1

P3

80/60

1.33

P4

30/60

.5

P5

35/60

0.5833

P6

25/60

0.4167

TrackSpeedAt(2)

Point IDResult (meters/second)

P1

80/60

1.33

P2

30/60

.5

P3

35/60

0.5833

P4

25/60

0.4167

P5

null

P6

null

TrackSpeedWindow(-1, 2)

Point IDResult (meters/second)

P1

[0, 1]

P2

[0, 1, 1.3]

P3

[1, 1.3, 0.5]

P4

[1.3, 0.5, 0.583]

P5

[0.5, 0.583, -0.4167]

P6

[0.583, -0.4167]

TrackCurrentAcceleration()

Point IDResult (meters/second²)

P1

0

P2

0.0167

P3

0.0056

P4

-0.0014

P5

0.0014

P6

-0.0028

TrackAccelerationAt(2)

Point IDResult (meters/second²)

P1

0.0056

P2

-0.0014

P3

0.0014

P4

-0.0028

P5

null

P6

null

TrackAccelerationWindow(-1, 2)

Point IDResult (meters/second²)

P1

[0, 0.0167]

P2

[0, 0.0167, 0.0056 ]

P3

[0.0167, 0.0056 , -0.0014]

P4

[ 0.0056 , -0.0014, 0.0014]

P5

[-0.0014, 0.0014, -0.0028]

P6

[0.0014, -0.0028]