3D modeling in some of the most rural environments on earth.

Recently I was able to join a friend on a scouting mission to eastern Tanzania to survey a couple of schools that were being considered for medium-sized solar power projects. These schools were hundreds of miles from any kind of grid and the solar powered would provide light for students to study at night, power for teacher houses, educational opportunities in renewable energy and a self-sustaining income for the schools.

So why do we need Sketchup here?!?

Picture this: You’re an American company that’s doing good energy development work in Africa. That’s all good except you’ve never been to the area you’re working in and you want to make sure you plan appropriately.

Wouldn’t it be neat to be able to fly through your project and the surrounding area? More interestingly wouldn’t it be fantastic to have a question about lengths or widths of a building on the other side of the world and be able to answer it by clicking on a ruler tool and measuring it yourself?

Accuracy without accuracy: Measuring

The GPS unit I was using told me it had an accuracy of +/-8m. That’s not terribly good on its own because it’s pretty much the length of a building.

There were two kinds of error I was trying to cancel out. First there’s individual point errors and then there’s a general GPS skew error where all points shifted one way on a map.

Of course the easiest way to correct for point errors would be to use surveying equipment or even a tape measure. This is rural Africa though and we didn’t have either of those things with us. What we did have was a little Garmin GPS unit so we had to make do.

By taking measurements at each corner of each building it was fairly simple to tell if any one point was badly taken by superimposing a rectangle on top of it.

I had no way of knowing how well lined up the aerial shot of the area was. In the end though the skew error was less crucial to correct since the data collected was being used to measure distances relative to individual buildings. The idea was to drop it onto Google Earth so by simply aligning the entire map with the aerial photograph of that area we got a level of aesthetic if nothing else.

Building the models

The models for the schools were created by using the photomatch tool in Google Sketchup. I had taken numerous pictures from the corners of each building and then used the awesome power of free software to map 3D textures onto giant cubes that I gradually chiselled, shaped, pulled and twisted into the shapes they were destined to be.

The destination for all this, as I said was Google Earth so I didn’t bother modeling each roof truss or window frame. If that data were needed I probably could’ve done it but I didn’t want to cause the little processor on my EEE PC any heartache so I tried to keep my models simple

Technology

This was all done using the free version of Sketchup running on a Windows 7 partition on my Eee PC 1005PE netbook. Thankfully the structures being modeled weren’t very complex and so my scrappy little netbook had no trouble working with the 3D and textures for each site. I did downsize the images a little from the 10MP originals so that the textures wouldn’t slow down the whole process.

Sketchup exports nicely to KMZ files which can then be opened by Google earth.

Google Earth

Once we had the models in Google earth the presentation aspect of the data can then begin. We had collected a lot of information about transportation routes, good hotels, restaurants, government offices and other important sites so it was easy to drop these onto the Google Earth map and create a tour to show how navigation from Kigoma to our project sites would look, finishing with a nice sweeping zoom to reveal the 3D, photo-real textured models from Sketchup.

Summary

This experience was definitely the most fun I’ve had with Sketchup so far. The simplicity of the models themselves were balanced by the technical challenges of getting accurate data with limited tools and working in an extremely rural setting.

Lens edge effects

One thing about most cameras is that things get a little distorted near the edges. Your straightest lines are usually going to be in the center of the frame. Knowing this now I really should have taken my pictures from farther back instead of trying to fill the frame.

Heights were also problematic. Because we didn’t take any actual measurements on site we needed to improvise. I did this by photographing Dennis next to a few buildings. Because I knew how high Dennis was it was fairly straightforward to then guess about the heights of the buildings.

Mistakes made / lessons learned:

• Take more and better pictures: going back to the site is not an option so be annoying with your camera and get it right the first time! Also I might consider using a narrower lens with less perspective and edge effects to get a flatter, more orthographic view which will, in turn, make modeling and photo matching easier.
• Measure: Packing a long measuring take wouldn’t have been a problem so next time it’s going into the bag. Simply having a few key points of reference in terms of height and width would have increased accuracy significantly.
• Realize your points of symmetry. I had modeled 3 schools before I realized that only the windows and wall colours were different.

I’ve had some feedback already that the data I presented was useful for previz and for planning cable lengths etc. I would be really interested in finding out where else we could use Sketchup in the developing world.