Comparing Elevation Data

Hello All,

Just wanted to share some recent results when comparing the elevation data accessible from various web api.  I was inspired by this application set up by Steve Young. For the test, I used a 400m swatch from a point somewhere in Catalunya. 

The three APIs used were the following:

Google Elevations API

Mapquest Open Elevation Service API

Geonames SRTM3 API

I also tested the USGS Elevation Service, but I was looking for API which allowed me to query globally.

Here are the results (441 locations queried):

As a side note, Grasshopper reports the requests for data came in at*:

1.9s for Google Elevations API

3.5s for Geonames

413ms for Mapquest

*this is not only measuring the request, but also has to take into account the request throttling due to the various API limitations.

As you can see, there is quite a difference in the data, especially when looking at what Google returns.  It is pretty clear that Mapquest and Geonames use very similar data coming from the SRTM3 dataset.  This dataset is at 3 arc-seconds (appx 90m) for most of the globe (up to 60ºN and 56ºS).  The resolution is 1 arc-second for the United States.  Google reportedly uses hundreds of data sources to achieve a finer resolution, though this comes at a cost.  Geonames and Mapquest put a limit of how many locations you can query at one time, with no limit per day (that I could find).  Google puts a limit of 2500 requests per day, with each request having up to 512 locations, or a total of 25,000 locations.

The comparison was made possible by some of the little utility components which are included in gHowl, namely the XYZ->GEO component which translates points in Rhino/Grasshopper to WSG84 coordinates.