The above are the main tools that I use in my workflow, but workflows are very dynamic, and there is always more than one way to skin a cat. The process of generating and optimising a 3D asset is predominantly the same, but the choice of tools that are available to help you achieve your required result are many, ranging in price from free to unattainably expensive for most mere mortals.

How do you approach a survey and actually create a 3D Asset?

First off, is the weather and lighting conditions. One of the most important aspects of photogrammetry, is that no matter what you are capturing, you need a good bright, but diffused light. Bright allows you to close the aperture of your camera down to maximise depth of field and capture nice sharp images with minimal noise present. Diffused light will mean that shadows on the object you are capturing will be kept to an absolute minimum … the light needs to be as flat as possible without harsh highlights or strong shadows. The same applies if you are capturing using a turntable indoors, your lighting needs to be diffused and bounced around the object evenly .. a light tent is perfect for this. There isn’t really any best time of day to carry out an external survey of an object/scene as long as the lighting conforms as mentioned above.

Secondly, the process of capturing has to be approached very logically. Lots of disparate photos of a subject won’t cut it. At the end of the day, the algorithms that produce models via photogrammetry are using very advanced pattern matching routines. We as humans can perceive the world around us adeptly, but unfortunately a computer is dumb, it doesn’t know what it is looking at and needs to be ‘taught’ to understand the depth and detail given to it via your image dataset. With this in mind, the photos that make up the survey need to be sharp, detailed and overlap each other by at least 50%. You must also photograph your subject from as many angles as possible so as to capture high detail in crevices, corners and overhangs. Often when you see the camera placement interpreted by photogrammetry software, you will notice that the person will have arced around the subject in many sweeps, both laterally and vertically (if possible).

Quite a number of my 3D Models cover quite large areas, not just a single small object such as a statue or rock. Unfortunately this can quite often present an operational problem. You can usually gain good access around a smallish individual object and thus get good coverage, but bigger means access is varied and the survey gets a whole lot trickier. Quite often parts of a large object/scene can’t be accessed close up and may involve shooting from different sides of a valley, in much wider sweeps around the subject, different banks of a river, etc … so how do you ensure that your photos continue to make sense to the computer? This is where ‘tie’ points come in, you need to look for patterns/detail that can be used as an anchor point and seen from completely different shooting positions, and make sure that there is enough overlap for the computer to understand that although some parts of an object/scene are not visible, these anchor points throw the software a lifeline to keep the chained pattern matching running smoothly.

Another hurdle to get to grips with larger surveys is that they quite often have so many surfaces to capture, it is quite easy to get lost and forget what you have taken, and that you have, in the end, shot a complete dataset that matches up. An example is a bridge (see below, blue rectangles = camera position), it seems simple to look at, but think about how many planes there are to capture from many (and I mean many) angles .. you have the cobbled river bead, the stone river walls, the grass and path crossing the bridge, the bridge walls from either side and from above, the wall running alongside the path, and the underside of the bridge. Each of these planes will need at least two passes of photos with at least 50% overlap and enough tie points to link each plane to the other. It is so easy for a survey to get away from you with this many things to remember, only to find when you get back to base, that the model cannot be generated successfully. A logical approach has to be adopted and rather than getting bogged down with what still needs to be photographed, it’s best to concentrate on one plane at a time, and then, if necessary, consider what needs to be done to get them all to match up in the 3D world.