When do we need media.csv?

[peterdesmet]

The media.csv is often the largest file to read, which is why read_camtrap_dp() initially had an option to skip it while reading data. We plan to remove that parameter to avoid complexity in further functions and not put the burden on the user to make this choice.

Alternative options to speed up reading:

1. Only select relevant columns from media (with col_select)
2. Only read media.csv in functions that actually need it (mostly write_ functions)
3. A combination of the two

For documentation, here's when I think we need media columns:

column	write_camtrap_dp()	write_dwc()	other functions
mediaID	yes	yes	yes (for reference)
deploymentID	yes	yes (for join)	yes (for join)
captureMethod	yes	yes	potentially (as filter)
timestamp	yes	yes	yes (for join)
filePath	yes	yes	potentially
filePublic	yes	yes	potentially
fileName	yes	yes (for sorting)	unlikely
fileMediatype	yes	yes	potentially (as filter)
exifData	yes	no	unlikely
favorite	yes	yes	unlikely
mediaComments	yes	yes	unlikely

So a potential solution could be to:

1. read_camtrap_dp() uses col_select and only reads mediaID, deploymentID, captureMethod and timestamp. This will speed up this function.
2. filter_ functions applied to deployments and observations also filter the media (on deploymentID, mediaID or a timestamp that falls between eventStart and eventEnd)
3. write_ functions read the full media.csv (can still be found using the $directory) and join with (potentially filtered) media already in memory. This will slow down those functions.

I don't know what the performance gain would be and if users are more likely to be patient when using read_camtrap_dp() or write_ functions. What is certain is that far more users will use read_camtrap_dp() than the write_ functions, so any speed gain benefits more users. I would wait and see if we hear about performance issues before considering the approach described above.

[peterdesmet]

Making media conditional adds complexity, so would always read media (as is done in https://inbo.github.io/camtrapdp/reference/read_camtrapdp.html).