Creating and showing topographic profiles on the Web

Topographic profiles are a classical field of interest in Earth Sciences, but they are also applicable to other disciplines and practical applications, such as environmental analysis, transportation and recreation. An interesting development is that everyone can create them using online elevation data and tools, even with options unavailable in desktop GIS softwares. Another development is the availability of JavaScript visualization libraries that allow displaying your own profiles on the web.

We start from topographic profile creation.

There are at least two web applications that allow to obtain topographic profiles from online data. In both cases, the base maps for defining the profile are Google Maps.

The former is Path Profiler at http://www.heywhatsthat.com/profiler-0904.html
It presents many parameters and choices for constructing profiles. Elevation source can be SRTM or Google elevations, on a flat or curved Earth. The vertical exaggeration can be changed, and profiles can strictly follow driving routes between chosen starting and ending locations.



The latter is Geocontext-Profiler at http://www.geocontext.org/publ/2010/04/profiler/en/
Elevation sources are Google elevations and profiles are only on a flat Earth (as of February 2011). This application can choose shortest, driving, bicycling and walking routes between locations. Resulting profiles contain more accompanying information and are more interactive (e.g., zoomable) than in the former case. More importantly, profile elevations can be copied as numeric data, so that one could use them for further processing (but remember license restrictions).
The resulting profile, with its accompanying Google Map, can be embedded in your web site, by simply copying and pasting a few code lines.



Now we consider a tool for displaying topographic profiles on the web, i.e. Protovis at http://vis.stanford.edu/protovis/

Protovis is a scientific visualization framework based on JavaScript and SVG (Scalable Vector Graphics), developed at the Stanford University by the Stanford Visualization Group.Choosing SVG implies that at least at the moment, Internet Explorer does not support it. These recent browsers support Protovis: Firefox, Safari, Chrome and Opera.
The documentation is well structured, and one can start playing by copying and modifying one of the various useful examples.

I illustrate a slightly different concept, i.e. showing the profile through a geological (more specifically, a glaciological) body, the Antarctic Ice Sheet. The example is largely based on Focus + Context at http://vis.stanford.edu/protovis/ex/zoom.html
Pan and zoom functions are available. The vertical scale can also be updated to accommodate the local variable heights. Originally displayed data represent a random time series, but this can be easily modified to accommodate a topographic profile and also a profile through a simple volume, as in the example of this post.

A surface bounded by a lower and an upper profile can be represented in Protovis by areas - http://vis.stanford.edu/protovis/docs/area.html -


The bedrock surface provides the bottom parameter, while the height parameter is the difference between the glacial surface and the bedrock elevations.

These surfaces derive from the BEDMAP database at http://www.antarctica.ac.uk/bas_research/data/access/bedmap/ . I created the profiles and exported them as numeric csv data with Saga. I converted them to the json format with Christopher Parker online converter at http://www.cparker15.com/utilities/csv-to-json/ .
The input data can be provided to the customization via a json data file, with three variables, distance along profile, bedrock elevation and glacial surface elevation.
In the zoom window, local statistical values of the ice thickness are also displayed.
The example url is http://www.malg.eu/blog/protovis2/prof_anta.html

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