If you've ever had to illustrate objects or people from weird angles for a client or otherwise then you should find today's post quit helpful. I actually recently came across this dilemma with a few of the children's illustrations I've been working on for my recent book. In one illustration I wanted a view of passengers getting ready to board the train but the perspective is from that of an ity bitty caterpillar in the hub of one of the trains wheels. So I needed to figure out how to get reference image of people from a perspective below street level. One obvious option is to have people lie down and try to get a picture from below them. the trouble with this is that their clothing will look wrong because the folds don't have gravity effecting them. A similar option would be to actually put yourself in that particular position and take a picture. If you're doing an illustration from above someones head looking down on them at strange perspective then just get up on something high and get someone to pose for you. Both of these will most likely give you trouble with the way the camera has translated the foreshortened limbs. There are a couple of other options I have enjoyed playing around with that don't include those wooden dolls you get at the art store.
For a while I have referenced a site called www.posemaniacs.com where you will find tons of poses of computer sculpted models . The best part about this site is that you can rotate around the poses to see them from all sorts of angles.
Another great option for models of people and other objects like cars, helicopters, building etc. can be found at www.3divia.com . This site is just amazing because once again you get to rotate around the poses and the objects. You have to do a quick download of there software but I've found it useful so far. I've only used the free models but I can just imagine how amazing the others must be judging from the free samples. How often do you really get the chance to rent a helicopter and take a photo of a house from above anyway? obviously you could spend hours looking for reference online but you won't get to choose the exact point of perspective you want unless you draw it all out, happen to know a drafting software or own a helicopter.
There is also the whole area of creating your own physical models out of clay, paper mache, wood, found objects etc. This works pretty good for very specific characters you've designed for a project. For example you may design an alien with all kinds of strange limbs so the best option most likely is to build your own model. For one of my books I got to do a bunch of illustrations of Noah's ark so I decided to take a few hours to actually build a small replica out of wood, shown below.
One final option I've used is called google sketchup which you can actually download for free and legally. This program allows you to build things from the ground up and then you can rotate around, under, above, zoom in and out etc. The trouble is that you will have to spend a bit of time figuring out the software but it's actually not too hard. I actually used this program to redesign my studio room. Now you could go all out and by the expensive programs but who really has the money for those?