Contours for Google Earth

[alanecharlesworth]

My idea was to enhance the Google Earth display with contours, so I could more readily visualize topography, especially in the higher ranges like the Himalayas and Andes.

Elevation data
I generated vector contours for Google Earth using the corrected SRTM03 (30m grid) world-wide elevation data created by Jonathan de Ferranti at http://viewfinderpanoramas.org/. The world-wide data set totals about 17 GB.

Contour generation
The elevation grid comes in 4x6 degree blocks. I used the Global Mapper GIS program on Windows to generate KML contours for each data block. (KML is the xml data format used by Google Earth). I chose a contour interval of 200m, a compromise between too many and too few lines and labels as one zooms in and out. I discovered how to specify KML regions, so I could make the contours disappear above an eye height of about 100 miles. That way one could navigate around the globe without clutter, then zoom in and see the contours lines.

Performance
I was very pleased when I discovered that Google Earth could handle all the contours for the whole world. (When I started, I had assumed I would have to open individual 4x6 blocks). It works fine on a 5 year-old Mac laptop and a 5-year old Mac Pro desktop. I have the data stored locally on each computer, and I leave the contours enabled when using Google Earth. I did try them out across a WiFi connection from laptop to desktop, and it still seemed usable. I have no idea if it it would be reasonable to access the contours from a web server, since I don't have a web site to try it out.

Installation
You can download the contour data from my Google Drive at:
https://drive.google.com/open?id=0ByN6O ... 3hrRVR5c2c

There is a 5 GB tar file with the entire world, and a 0.9 MB tar file with just North America.

Google Drive will complain: "There was a problem with the preview". Press the Download button.
It will then complain that the file is too big to scan for viruses. Press the Download anyway button.

When the download is complete: on a Mac, unpack the tar file by clicking on it. or on Windows 7 I used the open source 7-zip utility.

You should get a folder with 9 subfolders (for the world), or 1 folder (for North America) and the file "Contours.kml".

Open the Contours.kml file in Google Earth to access the contours. Google Earth dynamically loads what it needs. For convenience, open the sidebar, and move the Contours item from Temporary Places to My Places. To make the contours disappear, just uncheck the box to the left of its name in the sidebar.

I've attached a few screen shots showing what the contours look like. Sometimes they do not mesh perfectly with the imagery, presumably where Google is using different elevation data. If you zoom in too far, you'll be able to tell that these are relatively course contours.

Sometime in the offseason, I'll make US west contours (Rockies to the coast) using USGS data and a finer contour interval (perhaps 200').

PS, I have no idea what limits Google might place on download bandwidth of this stuff. I test-downloades the 5 GB this morning, and it downloaded at 4 Gbytes/sec over comcast.

[Webfoot]

That looks useful. I shall give this a try. Thanks!

[Lurch]

A 5 gig KML? no thank you

[kepPNW]

A 5 gig KML? no thank you

It's actually mind-blowingly efficient, due to what I must assume is the tiled nature of it. Need to study the guts, to see how I might be able to improve some of my own!

[sprengers4jc]

Awesome. Thank you!

[Koda]

with just a few mouse clicks you can overlay the USGS topo map over the 3D Google Earth imagery.

[Webfoot]

with just a few mouse clicks you can overlay the USGS topo map over the 3D Google Earth imagery.

I have a pile of overlay options, that being one of them, but I don't believe I have another set of transparent contour lines like alanecharlesworth produced.

[aiwetir]

with just a few mouse clicks you can overlay the USGS topo map over the 3D Google Earth imagery.

I have a pile of overlay options, that being one of them, but I don't believe I have another set of transparent contour lines like alanecharlesworth produced.

I believe there is a set at CalTopo, but I have no idea how to get them on Earth. They are included in GaiaGPS for my phone.