Create a CSV with the coordinates from geotagged photos

Recently I took a lot of photos on my phone during fieldwork (survey for the NERC-ARF LiDAR and hyperspectral calibration flights) and wanted to extract the GPS coordinates from each photo so I could load them into QGIS using the add delimited text dialogue. The aim wasn’t to have precise locations for each photo (GPS positions for each of the points surveyed were recorded separately) but to give a quick idea of the locations we’d visited before the main GPS data were processed.

I while ago (2012!) I wrote a script for this task. The script (CreateJPEGKMZ) requires pillow and the imagemagick command line tools.

It code isn’t particularly tidy (despite my recent updates) but it basically pulls out the GPS location from the EXIF tags and writes this to a CSV file. To create a KMZ a thumbnail image is created and a corresponding KML file. Both the thumbnail and KML are then zipped together to generate the KMZ which can be opened in GoogleEarth.

To use the script to write a CSV file:

CreateJPEGKMZ.py --outcsv gps_points.csv input_jpeg_files

To also create KMZ files for each photo:

CreateJPEGKMZ.py --outcsv gps_points.csv \
                 --outkmz output_kmz_files 
                 input_jpeg_files

This was also a good lesson in the benefits of having scripts in version control and publicly available.

Create a GIF from a series of images

Creating a video is a cool way to visualise a time series of remote sensing data / outputs. Rather than creating a full video you can also use a GIF. One advantage of GIFs is you can embed them in Powerpoint presentations and they should will play in presentation mode (I’ve found them more reliable than videos in other formats).

You can use the ImageMagick convert command to create a GIF:

convert -delay 20 -loop 0 in_files/*.png out_animation.gif

However, depending on how your files are named it might not sort the numbers as expected leading to jumps in the video. This problem was addressed in the following post on the ‘remotelysensible’ blog:

Alphanumeric string sorting in Python

This can be used to sort the files in Python then call the convert command using subprocess:

#!/usr/bin/env python

import argparse
import re
import subprocess

re_natural = re.compile('[0-9]+|[^0-9]+')

def natural_key(s):
   """
   Natural sorting function from http://stackoverflow.com/questions/12184015/in-python-how-can-i-naturally-sort-a-list-of-alphanumeric-strings-such-that-alp
   """
   return [(1, int(c)) if c.isdigit() else (0, c.lower()) for c in re_natural.findall(s)] + [s]

if __name__ == '__main__':
   parser = argparse.ArgumentParser(description='Create an animated gif from a series of images')
   parser.add_argument("images", nargs='+',type=str, help="Input images")
   parser.add_argument('-o', '--outgif',
                       metavar ='Output gif',
                       help ='Output name for gif',
                       required=True)
   args=parser.parse_args()

   sorted_png_files = sorted(args.images, key=natural_key)

   convert_cmd = ['convert','-delay','20','-loop','0']
   convert_cmd.extend(sorted_png_files)
   convert_cmd.extend([args.outgif])

   subprocess.call(convert_cmd)

The script is run using:

python create_gif.py -o out_animation.gif in_files/*.png 

As well as creating GIFS of a time series you can use SPD 3D Points Viewer to export images of a point cloud as it rotates and create a gif from these similar to this video of airborne LiDAR data over Lake Vyrnwy on YouTube: https://www.youtube.com/watch?v=P_9998KJib4

The script can be downloaded from GitHub. Note the delay is hardcoded at 20/100th of a second but this can be changed if needed.

Create an animated GIF from a series of images

ImageMagick is a collection of command line tools which allows you to do lots of cool things with images. I use it a lot to create animations, in particular to add multiple images and text to a single slide. If you want to make something simpler than a movie, it is possible to generate a gif animation using ImageMagick. The simplest command is:

convert -delay 100 *files.png animation.gif

Which will create an animation from all files matching ‘*files.png’ with a 100 x 1/100 s (1 s) delay between images.

If you want to add a title for each image you can also do this with ImageMagick, using something similar to:

convert image.png -gravity south \
 -strokewidth 10 -pointsize 100 \
 -fill white -annotate 0 "Title" \
 image_with_title.png 

An example script, using RSGISLib to colour images and imagemagick to create a GIF, is available on github.