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filters.mongo

The Mongo Filter applies query logic to the input point cloud based on a MongoDB-style query expression using the point cloud attributes.

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Example

This example passes through only the points whose Classification is non-zero.

[
    "input.las",
    {
        "type": "filters.mongo",
        "expression": {
            "Classification": { "$ne": 0 }
        }
    },
    "filtered.las"
]

This example passes through only the points whose ReturnNumber is equal to the NumberOfReturns and the NumberOfReturns is greater than 1.

[
    "input.las",
    {
        "type": "filters.mongo",
        "expression": { "$and": [
            { "ReturnNumber": "NumberOfReturns" },
            { "NumberOfReturns": { "$gt": 1 } }
        ] }
    },
    "filtered.las"
]

Options

expression
A JSON query :ref:`expression` containing a combination of query comparisons and logical operators.

Expression

A query expression is a combination of comparison and logical operators that define a query which can be used to select matching points by their attribute values.

Comparison operators

There are 8 valid query comparison operators:

  • $eq: Matches values equal to a specified value.
  • $gt: Matches values greater than a specified value.
  • $gte: Matches values greater than or equal to a specified value.
  • $lt: Matches values less than a specified value.
  • $lte: Matches values less than or equal to a specified value.
  • $ne: Matches values not equal to a specified value.
  • $in: Matches any of the values specified in the array.
  • $nin: Matches none of the values specified in the array.

Comparison operators compare a point cloud attribute with an operand or an array of operands. An operand is either a numeric constant or a string representing a dimension name. For all comparison operators except for $in and $nin, the comparison value must be a single operand. For $in and $nin, the value must be an array of operands.

Comparison operator specifications must be contained within an object whose key is the dimension name to be compared.

{ "Classification": { "$eq": 2 } }
{ "Intensity": { "$gt": 0 } }
{ "Classification": { "$in": [2, 6, 9] } }

The $eq comparison operator may be implicitly invoked by setting an attribute name directly to a value.

{ "Classification": 2 }

Logical operators

There are 4 valid logical operators:

  • $and: Applies a logical and on the expressions of the array and returns a match only if all expressions match.
  • $not: Inverts the value of the single sub-expression.
  • $nor: Applies a logical nor on the expressions of the array and returns a match only if all expressions fail to match.
  • $nor: Applies a logical or on the expressions of the array and returns a match if any of the expressions match.

Logical operators are used to logically combine sub-expressions. All logical operators except for $not are applied to arrays of expressions. $not is applied to a single expression and negates its result.

Logical operators may be applied directly to comparison expressions or may contain further nested logical operators. For example:

{ "$or": [
    { "Classification": 2 },
    { "Intensity": { "$gt": 0 } }
] }
{ "$or": [
    { "Classification": 2 },
    { "$and": [
        { "ReturnNumber": "NumberOfReturns" },
        { "NumberOfReturns": { "$gt": 1 } }
    ] }
] }
{ "$not": {
    "$or": [
        { "Classification": 2 },
        { "$and": [
            { "ReturnNumber": { "$gt": 0 } },
            { "Z": { "$lte": 42 } }
        ] }
    ] }
}

For any individual dimension, the logical and may be implicitly invoked via multiple comparisons within the comparison object. For example:

{ "X": { "$gt": 0, "$lt": 42 } }