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Purpose: Fully describe the Create PNGWalk Feature, and the PNGWalk Tool.

Audience: Scientists

See also:


  1. Introduction
  2. Create PNG Walk
    1. Autorange Some, But Not All, Axes
  3. PNG Walk Tool
  4. Basic PNGWalk

1. Introduction

PNG Walks are a set of images which together study a mission which cannot be captured in one image. These are typically daily plots from a many-year mission. We want to be able to quickly flip through images to find unusual events, for example. If we were to do this using Autoplot interactively, we might be limited by the time the data takes to load. In this case we can set up the PNGWalk to run over night, and then use the PNGWalk Tool to flip through plots in the morning.

Autoplot is able to both produce PNG Walks and look at them. To look at them, the PNG Walk Tool is used, which lets you flip through images quickly, looking at thumbnails and using the mouse wheel.

2. Create PNG Walk

  • Template used to specify the file names and implicitly the interval size.
  • Orbits can be used to create files by orbits.

2.1. Autorange Some, But Not All, Axes

Autoplot v2018a_3 now allows some of the axes to autorange, while others are fixed. In the vap (or current configuration), edit each axis so that its "autorange" property is set if you intend for it to be autoranged. Axes where this is not set are left alone.

See also, which allows additional hints (like include zero or select width from a set of possibilities) to be set.

3. PNG Walk Tool

  • Any set of images can be loaded, they need not be the same size or time tagged.
  • The "QC" (Quality Control) tool can be used to annotate images when the files are local.
  • clicking on the image will give plot coordinates. This is done by looking for special metadata within the PNG files.
  • The QC tool can also be used to create tutorials, where a script grabs captions from the QC files.

4. Basic PNGWalk

  • A set of files in a directory. These are loaded with ".../*.png" for example. png, jpg, and gif images are supported.
  • the directory can be a local folder, a web folder, or within .zip file (as any Autoplot data can be).
  • thumbs subdirectories can exist but are not required.
    • thumbs100 are thumbnails roughly 100 pixels corner to corner
    • thumbs400 are thumbnails roughly 400 pixels corner to corner
    • directories should contain thumbnail images with the same filename as the full-size image.
    • if the file is not found, a thumbnail is generated from the full-size image (but not stored).
  • "QC" files are files containing annotations for the files. This will be the image filename, plus .ok or .problem extensions.
    • the QC tool can be used to read and further annotate files.
    • annotation is only supported for local files and when ftp is used.
  • png files can contain axis information, so that pixel-to-data transformations can be done.
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