Expression Syntax

The PDAL expression syntax is a subset of that found in a great many programming languages. Specifically, it uses a limited set of operators from the C language. Dimension names can be used where a variable or constant would be used. Double-precision constants are supported.

All mathematical operations are done with double-precision floating point. There is no automatic conversion of numeric values to logical values. For example, the following is not permitted:

((Intensity > 0) && Classification)

Instead, you must write:

((Intensity > 0) && (Classification != 0))

Mathematical Operators

Operator	Function	Example
*	Multiplication	Intensity * 64.0
/	Division	Green / 255
+	Addition	Classification + 255
-	Subtraction	X - 64215.2

Logical Operators

Operator	Function	Example
!	Not	!(X < 25)
>	Greater	X > 52.523
>=	Greater Than or Equal	X >= 52.523
<	Less	Y < -28.456
<=	Less Than or Equal	X <= 0
==	Equal	Classification == 7
!=	Not Equal	Classification != 7
&&	And	Classification == 7 && Intensity > 64
||	Or	Classification == 7 || Classification == 8

The order or operations is as listed, which matches that of the C language. Parentheses are supported to alter the order of operations.

Examples

((Classification == 7 || Classification == 8) && NumberOfReturns == 1)

Selects points with a classification of 7 or 8 and number of returns equal to 1. Note that in this case the parentheses are necessary.

X > 2500 && X < 4700 && Y > 0

Selects points with an X between 2500 and 4700 and a positive Y value.

(NumberOfReturns > 1 && ReturnNumber == 1)

Selects “first” returns from a laser pulse.

!(NumberOfReturns == 1)

Selects only those points where the laser pulse generated multiple returns.