Web Service as a Look-Up Table to Refine GPS Data

Elevation data recorded by GPS devices is notoriously inaccurate, especially in hilly terrain like the Russian River Valley example from our earlier post.

The final elevation track plotted from the Russian River Valley GPX file is suspicious for several reasons. First, the graph shows we descended almost 50 feet below sea level. That’s hard to believe, since we were travelling along the bank of the river, only about 10 miles from the Pacific Ocean.

Secondly, we were headed mostly west, following the river downstream, but the track shows a predominantly uphill trend.

We can evaluate the recorded GPS elevation data by comparing it to information available from the United States Geological Survey (USGS). The USGS operates a Web service that accepts latitude and longitude coordinates, and returns elevation data measured by NASA and assessed for accuracy based on over 13,000 control points in the continental United States.

Using the elevation Web service in an Altova MapForce mapping will let us extract each point from the GPX file, send the coordinates to the USGS Web service, and build a new GPX file with corrected elevation data.

Data Mapping Patterns

Altova MapForce includes powerful mapping components that correspond to design patterns for data transformation requirements. Analyzing a data mapping assignment up front and following a few straightforward guidelines can help simplify creation of the mapping design and lead to an optimal solution.

The MapForce Examples project provides sample mapping files and data sets that illustrate many common data mapping patterns. Reviewing these examples and executing them with the MapForce Built-in Execution Engine is another good way to help select the best pattern for your own project.

Exact vs. Conditional Matching

First, determine whether your inputs and outputs have an exact one to one relationship or require analysis of a more complex condition such as from-to ranges or an if-else statement.

We will be at TechEd! Will you?

Altova will be exhibiting in sunny Orlando, FL from June 11 – 14 at Microsoft TechEd in booth #2338.  Come on down to the Orange County Convention Center and talk with our experts about the new features in the Altova MissionKit.


If you are attending TechEd, stop by our booth to see the latest features in the Altova MissionKit 2012r2, which include EPUB editing and validation in XMLSpy, sorting of data mapping results in MapForce, generation of code from UML sequence diagrams in UModel, RichEdit functionality in StyleVision and Authentic and much more! We hope to see you next week.