Wednesday, July 4, 2012

Google Research Update & Elevation Profiler

See Labels > Google Research Project in the right column to see earlier posts about this project.

Work on our Google Project is going well:

- On the content front, after feedback from team members and talk aloud 'hallway' testing, the final version of the Google Earth tours needed for the tests have been produced.  
- On the testing software front Paolo has got the system working where we record both eye-tracking of subjects using our tours and events in the Google Earth API (e.g. tracking camera movements by the subject).  We are exploring the idea of combining the results from both but at the moment we cannot combine them directly for analysis.  

Google Earth tour Sound: We have identified that there is incompatibility between playing sound on Macs and PCs from tours.   When he has some time, Paolo has promised to write up a HowTo post here on a work around.

Elevation Profile in Google Earth:  As part of the work I've been thinking about how to use cross sections or elevation profiles to visualize topography.  I thought I'd write up some features of the elevation profiler I've explored that are quick and easy to use for showing elevation.   

Problem:  I want to show the user the topography of a river valley.  In areas of dramatic topography such as the Grand Canyon you can just tilt the Google Earth camera and the user gets the idea of what the valley is like.  However, in our study area the valley landscape I want to show is much more subtle, the slopes need to be exaggerated to show up.  Also, when you are considering topography across a large distance (say the elevation of the Amazon) topography will naturally be subtle compared to the long length of the feature.

Solution:  Use an elevation profile feature of lines to exaggerate the topography.


1] Find the area you want to draw a cross section across.  Use the path tool (its a button on the top line of Google Earth with a line with blobs icon) draw a simple line across part of the feature, you should use a click ONLY at the start and the end. 

2] Once you have named and saved your line, find it in the places column to the left.  Right click it and select 'Show elevation profile'.  An elevation cross section will appear at the bottom of the screen.  You can click within the profile and a red arrow will appear on screen to show the elevation at any point on your line.

3] move the mouse within the elevation and a vertical line and red arrow show the height at any point.  

4] A nice trick is to draw a deliberately short line section and lengthen it.  To do this, right click the line in places column > properties.  Now find the end of the line you marked (a blue or red square) and click and drag it.  As the line lengthens the profile dynamically grows.  This allows for all kinds of teaching questions, e.g. in my case I could start with the line going down just one slope and ask students to predict the rest of the profile on paper.  You then complete the profile dragging the line out and the true cross section is revealed and have a competition on who drew the best profile.

Teaching Point:  Its important to remind the students that what they're looking at is an exaggerated section otherwise they may get the idea that the topography is as dramatic as it looks.  I would do this by tilting down to view the line in Google Earth and asking the students why the topography doesn't look the same as the profile.  You could also ask them to calculate what the exaggeration is by reading off values from the vertical and horizontal axes.

1 comment:

QUÂN HỒNG said...

How to know river cross section? when I did it in Google Earth, it only displace surfacewater level, can I see the river cross section by google earth? I did it by Digital Elevation Model file, but seem my DEM is not good, can not applicable. Thanks