With the 0.9 release of WebODM we are introducing the ability to preview and export contours directly from map view. This has been a much requested feature and we decided to take on the work to implement it.
Behind the curtains we used the GRASS GIS engine which already powers the volume measurement plugin to do the contours calculation, with some help from GDAL/OGR. The beauty of using a familiar language to power these computations is that it’s really easy (if you are familiar with GRASS) to understand how the information is calculated. No mistery. It’s all here.