Seeing imperfect orthorectifcation in Google Earth imagery

Yesterday we talked about orthorectification and how it is imperfect, especially when using an inaccurate terrain model. We thought we would have a look at the effect using historical imagery. We used a variation on two JavaScript tools we have created in the past for animating historical imagery using the Google Earth plugin and using Google Earth Tours. This enabled us to create tours which animate only a selection of historical imagery and exclude lower quality images. Because Google Earth does not allow us to play the tours at a reasonable speed (it omits images), we recorded the tours and then sped up the recording.

We chose three locations that we know have significant elevation variation as well as a lot of satellite imagery. They are Devil’s Peak, Cape Town, South Africa, Rio de Janeiro, Brazil, and Calama, Chile.

If you look carefully, you can see that some locations move more than others.

The buildings at 1 and the bridge at 2 seem to move much less than the surrounding imagery. This suggests that the terrain model for these locations is closer to the true altitude than for surrounding areas.

You can download the Google Earth tours we used to create the video here.

About Timothy Whitehead

Timothy has been using Google Earth since 2004 when it was still called Keyhole before it was renamed Google Earth in 2005 and has been a huge fan ever since. He is a programmer working for Red Wing Aerobatx and lives in Cape Town, South Africa.






PLEASE NOTE: Google Earth Blog is no longer writing regular posts. As a result, we are not accepting new comments or questions about Google Earth. If you have a question, use the official Google Earth and Maps Forums or the Google Earth Community Forums.



PLEASE NOTE: Google Earth Blog is no longer writing regular posts. As a result, we are not accepting new comments or questions about Google Earth. If you have a question, use the official Google Earth and Maps Forums or the Google Earth Community Forums.