# filters.gpstimeconvert

The gpstimeconvert filter converts between three GPS time standards found in lidar data:

1. GPS time (gt)

2. GPS standard time (gst), also known as GPS adjusted time

3. GPS week seconds (gws)

Since GPS week seconds are ambiguous (they reset to 0 at the start of each new GPS week), care must be taken when they are the source or destination of a conversion:

- When converting from GPS week seconds, the GPS week number must be known. This is accomplished by specifying the start_date (in the GMT time zone) on which the data collection started. The filter will resolve the ambiguity using the supplied start date.

- When converting from GPS week seconds and the times span a new GPS week, the presence or absence of week second wrapping must be specified with the wrapped option. Wrapped week seconds reset to 0 at the start of a new week; unwrapped week seconds are allowed to exceed 604800 (60x60x24x7) seconds.

- When converting to GPS week seconds, the week second wrapping preference should be specified with the wrap option.

Note

The filter assumes points are ordered by ascending time, which can be accomplished by running filters.sort prior to `filters.gpstimeconvert`. Note that GPS week second times that span a new GPS week should not be sorted unless they are unwrapped.

## Example #1

Convert from GPS time to GPS standard time.

    [
        "input.las",
        {
            "type":"filters.gpstimeconvert",
            "conversion":"gt2gst"
        },
        "output.las"
    ]

## Example #2

Convert from GPS standard time to unwrapped GPS week seconds.

    [
        "input.las",
        {
            "type":"filters.sort",
            "dimension":"GpsTime",
            "order":"ASC"
        },
        {
            "type":"filters.gpstimeconvert",
            "conversion":"gst2gws",
            "wrap":false
        }
    ]

## Example #3

Convert from wrapped GPS week seconds to GPS time.

    [
        "input.las",
        {
            "type":"filters.gpstimeconvert",
            "conversion":"gws2gt",
            "start_date":"2020-12-12",
            "wrapped":true
        },
        "output.las"
    ]

## Options

conversion

  The time conversion. Must be one of the following: “gst2gt”, “gst2gws”, “gt2gst”, “gt2gws”, “gws2gst”, or “gws2gt”. [Required]

start_date

  When the input times are in GPS week seconds, the date on which the data collection started must be supplied in the GMT time zone. Must be in “YYYY-MM-DD” format. [Required for the “gws2gt” and “gws2gst” conversions]

wrap

  Whether to output wrapped (true) or unwrapped (false) GPS week seconds. [Default: false]

wrapped

  Specifies whether input GPS week seconds are wrapped (true) or unwrapped (false). [Default: false]