How to incorporate stdmetrics in gridmetrics function?

Question

I am attempting to feed the lidR gridmetrics function a list of metrics. I can generate the list of metrics within a function (following this example):

myMetrics = function(z, i)
{
 metrics = list(
 zmean = mean(z),
 imean = mean(i),
 zwimean = sum(z*i)/sum(i), # Mean elevation weighted by intensities
 zimean = mean(z*i), # Mean products of z by intensity
 zsqmean = sqrt(mean(z^2)) # Quadratic mean
 )
 return(metrics)
}

And then feed the list into the gridmetrics function:

metrics = grid_metrics(lidar, myMetrics(Z, Intensity), 20)

However, I cannot find a way to incorporate individual stdmetrics into the above myMetrics function.

How, for example, would I add the zqx or zkurt metrics (from this source) into the myMetrics function, which can then be fed into the gridmetrics function?

Answer 1

You can use the function stdmetrics inside your custom function like in the following example (using stdmetrics_z)

myMetrics = function(z, i)
{
 lidrmetrics = stdmetrics_z(z)
 mymetrics = list(
 zwimean = sum(z*i)/sum(i), # Mean elevation weighted by intensities
 zimean = mean(z*i), # Mean products of z by intensity
 zsqmean = sqrt(mean(z^2)) # Quadratic mean
 )
 return(c(mymetrics, lidrmetrics))
}
metrics = grid_metrics(lidar, myMetrics(Z, Intensity))

Of course if the function requires more inputs you must update the parameters of your custom function. This is documented in the examples of help("stdmetrics").

Also the following works too.

metrics = grid_metrics(lidar, c(myMetrics(Z, Intensity), stdmetrics_z(Z)))