Q:

Calculating speed along point feature class (.gpx) in ArcMap?

I have imported a .gpx file into ArcMap as a point feature class.
Each feature has a Point z as well as a DateTime.
I want to create a graph that shows speed as a function of distance. How do I do this?

A:

I did a presentation a few years ago where I developed a tool to take GPX points and create a line featureclass by rows where the speed is indicated as an attribute. You can symbolize the output by that field in ArcMap. Natural breaks seems to symbolize it well.
I just uploaded the tool to arcgis.com, you can download it here.
After you get the line, you can use the line as input to a graph from the View > Graph menu (in ArcMap). Or you can use the Feature Vertices to Points tool to turn the line back into points with the speed attribute attached and turn those into a graph. Your value field will be speed
Alternatively, you can hack the script or write you own code as you know the most important part to finding speed: distance / time

