seascape models

Part 1: Extracting exif data from photos using R

See the other parts in this series of blog posts.

My camera comes with an inbuilt GPS allowing you to geo-reference photos you take. Here is a simple example for how we can use this feature to create an interactive web map in R.

The photos come from a survey I did of oysters on a rocky shoreline. I took photos of each quadrat enabling me to geolocate the quadrats as well as record what occurred within them.

First get your hands on a few packages, exif for extracting exif info in R, dplyr for data management and leaflet for making maps:

library(exifr)
library(dplyr)
library(leaflet)

Now set your working director the a folder that holds the photos in questions. We can then get the names of all the photos straight into R’s memory like this:

files <- list.files(pattern = "*.JPG")
dat <- exifr(files)

The pattern argument ensures we just grab the jpegs from the folder and nothing else. Neat, we have our exif info as a dataframe. Now let’s select just the useful columns:

dat2 <- select(dat,
	SourceFile, DateTimeOriginal,
	GPSLongitude, GPSLatitude,
	GPSTimeStamp)

	write.csv(dat2, 'Exifdata.csv',
	row.names = F)

NB the select function comes from the dplyr package. You can do this with base R too, but I prefer dplyr. (You can get my dataframe here)

You can make a quick map of locations like this:

plot(dat$GPSLongitude, dat$GPSLatitude)

Make an interactive map

Interactive web maps are easy with the leaflet package. We can plot the same points over and ESRI provided satellite image like this:

leaflet(dat2) %>%
addProviderTiles("Esri.WorldImagery") %>%
addMarkers(~ GPSLongitude, ~ GPSLatitude)

And here’s what it should look like:

Next up we will look at how to match these locations to the quadrat data I collected. I will also show you how to add photos to the pop-ups at the site locations.

Contact: Chris Brown

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