bomthegov can assemble basic timelapse videos from the images you have collected for a BOM identifier.
Images are collected in the 'images' folder, and are organised by image type, and then ID.
So for example: images/radar/IDR023 ... IDR024 ... and so on.
The folder structure is created depending on what you fetch, and you can fetch for as long as you like (or have disk space for).
All images in an image set will be used to build a timelapse. So for example, if you've collected an entire set of satellite images from the past 2 hours, and run the build timelapse command on that image set, your timelapse will be built of the files from those 2 hours. At the moment, bomthegov does not ignore any frames from a collected image set, so whatever images are in the 'images' folder for that ID, is what will be used to build your timelapse.
To begin the process of building a timelapse from a list of available images, you can run:
bash bomthegov timelapse list
That will show you a list of IDs that are ready to timelapse, and ask you questions about what maximum resolution and Frames Per Second (FPS) rate you want the video to be.
If you know the ID of the image set, and you wish to timelapse right away from the command line (with resolution and FPS defaults), you can specify the ID to process, like so:
bash bomthegov timelapse IDR024
and bomthegov will start building a timelapse for that ID immediately/uninteractively.
You can set up bomthegov to build timelapse videos non-interactively by specifying the ID of the image set, along with the answer to provide to all interactive questions.
For example, the line below will build a timelapse for IDE00105 and set the answer to 'yes' for any interactive questions, and then automatically and non-interactively build the timelapse video with the default technical specifications, as outlined at the end of this doc:
bash bomthegov timelapse IDE00105 yes
Note: If any bomthegov arguments are invoked as a cronjob (not just timelapse arguments), the default answer to any question will always be 'no'.
Currently, non-interactive/auto mode is only available for timelapse builds. The command does not apply to image fetching, software updates, or image storage resets.
bomthegov uses the software package imagemagick to convert satellite and radar images into usable video frames, and then passes those frames to a video encoding tool called ffmpeg to assemble a timelapse video.
The conversion process is likely to be resource-intensive on RAM, CPU, and disk, and depending on how many images need to be converted to video frames, and their original resolution, building the timelapse video may take a long time.
Once a timelapse has been successfully created, bomthegov will notify you, and then ask if you would like to remove the ID from the timelapse list/move the collected image set to a folder called '.archive' so that your image collection for that same ID starts "fresh" for a new timelapse. Your previously collected images are not deleted during this process, they're simply compressed into an archive file (TAR), and moved to the '.archive' folder inside 'images' where you can either use/merge them again later, or delete them manually if you choose.
You can explore the archived images sets yourself here:
images/.archive/
If you would like to 'clean up' all your stored image sets and archives to start from scratch, you can specify the 'reset' option:
bash bomthegov reset
which will delete everything in 'images' (including the '.archive' folder).
Previously prepared timelapse videos will not be deleted in a reset.
The default maximum video resolution and Frames Per Second (FPS) for timelapse videos is 4096x2160 (4K) at 25fps.
HD, 720p, and lower resolutions are available in interactive mode by running:
bash bomthegov timelapse list
which will guide you through the settings interactively.
Note: The maximum video resolution size is only available from source images that are larger than that resolution---i.e. the source imagery is only downscaled, it is not upscaled. So for example, if the imagery from a satellite or radar is originally in HD, then HD will be the maximum video resolution, even if 4K is selected.
For instance, most of the IDE004xx satellites are able to be timelapsed in 4K, many of the other satellite and radar image sets aren't.
All timelapse videos export to MP4 video format, which should make them streamable on the web, and viewable on mobile devices. The MP4 codec is H.264 (AVC) which is supported on a wide range of devices and browsers.
The maximum video bitrates for each resolution size are:
- 4K at 24mbps
- HD at 18mbps
- 720p at 4mbps
- anything else at 2mbps
Timelapses are encoded in two-passes at these bitrates to ensure the best outcome between the highest image quality versus file-size compression.