Markers#

Overview#

This tool allows for interactively creating markers in any viewer and logging information about the location of that marker along with the applicable data and viewer labels into a table. It also allows the user to measure distances between points in a viewer.

UI Access#

Details#

With the Markers tool open in the Information tab, mouse over any viewer and press the “m” key to log the information displayed in the app toolbar into the table. The markers remain at that fixed pixel-position in the viewer they were created (regardless of changes to the underlying data or linking, see Linking of datasets in glue) and are only visible when the plugin is opened.

When images are WCS linked, the table also exposes columns labeled “pixel:unreliable”, “world:unreliable”, and “value:unreliable”. These will be logged as True in cases where the information is outside the bounds of the reference image’s WCS (noted in the mouseover display by the information showing as grayed).

Distance Tool#

The Markers plugin also includes a tool for measuring the distance and position angle between two points in a viewer. This functionality is available whenever the Markers plugin is open.

  1. Mouse over the desired start point in a viewer and press the d key. A ... indicator will appear in the Last Measured Distance field at the bottom of the plugin, showing that the first point is set.

  2. Mouse over the desired end point and press the d key again.

This will draw a line between the two points. A label showing the distance will appear, rotated to be parallel with the line, and offset to prevent intersecting the line.

A new table, Measurements, will also appear below the main markers table. This table logs the start and end coordinates (both pixel and world, if available), the on-sky separation, the pixel distance, and the position angle for each measurement.

Additional Features:

  • Snapping: To measure the distance from or to an existing marker, hold down the Alt key (or Option on Mac) when you press d. The tool will “snap” to the nearest marker already in the main table.

  • Clearing: Pressing the r key will clear all markers from the main table and all distance lines from the viewers.

API Access#

To export the table into the notebook or clear the table via the API:

markersplugin = jd.plugins['Markers']
t = markersplugin.export_table()
markersplugin.clear_table()