"S" Mountain Salida, CO

Hi there, Blake.

I'm not sure if you saw my comments on your earlier synth, but you make some good observations on your own.

Your continuous overlapping coverage of the graffiti on the water tank and the nature of its highly unique texture makes the result spectacular.

The colourful tree, by contrast, has a surface many many times more complex. More importantly the different branches of the tree block each other out from different points of view and the branches are so small that the texture on one side of a branch in one photo is quickly rotated out of view as you circled the tree. Moreover, since none of the branches are particularly large in the frame of the photos and the photos around the tree are relatively sparse, it was impossible for Photosynth to match any texture on the branches that was seen in three or more of the photos. I would expect the trunk to be successfully represented in the pointcloud long before the branches, based simply on size.

24 photos is a good minimum number of photos when circling an object. In the tree's case the uneven ground and nearby shrubs surrounding it is difficult to complete a clean circuit but as it is, at your close range I counted only 10 photos moving from one side to the other.

I made this sort of mistake many times when I began synthing and I am still looking for ways to beat it on very large and complex objects. I remember reading in the Photosynth Photography Guide (available here: http://photosynth.net/howtosynth.aspx ) when I began that I should have three photos of something from three different angles in order for Photosynth to detect and position it correctly. What I began realising after I had some breakthrough successes was that I had to stop thinking of objects as single objects, but as a collection of separate surfaces. For great pointclouds you need some overlap in addition to a decent coverage of each surface in the object.

Photosynth can only make jumps between photos that are all pointed at the same place on the same surface that differ by a maximum of 30 degrees.

Photosynth fundamentally works by matching unique textures. From this, we can see exactly why the water tank was so successful and why the star was such a failure. The primary textures in the photos of the star were either the mountains behind it or the clouds further behind it. The star in itself is nearly invisible to Photosynth because it can't determine any repeating texture.

With objects which have no blatant texture or which have extremely complicated surfaces, the number of photos necessary to derive a pointcloud (whether detailed or at least not malformed) jumps up significantly in order for Photosynth to track their features and therefore calculate the positions of those features.

The simplest way to lock Photosynth into succeeding in tracking something is to provide a dense orbit of photos around a surface.

The tradeoff for this way of forcing Photosynth to get something right (the orbit) is that you must understand when an orbit is overkill or when to use a dense orbit versus a sparse orbit.

In the above case, where you want to cover an environment with multiple objects within the scene, trying to capture an orbit of photos for every surface (even if your camera had enough space on the memory card) would almost certainly choke your computer when you tried to reconstruct the scene with the synther. Shooting full orbits around different parts of individual objects can easily work, but you don't get the joy of seeing the entire scene in the pointcloud all together.

This may change by the end of 2010 if the Photosynth team completes 'synth linking' this year (no promises there, though). I see that you've geotagged your synth above, but can't tell whether you also geoaligned it. Assuming that you have, the idea is that you will be able to navigate all geoaligned synths.

This means that synthing individual objects and geoaligning them may, in the end, be a better approach than trying to pack an entire environment into a single synth.

I'll admit, though, that until synth linking is in our hands the desire to synth an entire scene is very powerful and there's nothing to say that you shouldn't.

I will say that you may find better success in mastering synthing different types of individual objects. Once you nail that down and get a feel for about how many photos are necessary for the desired detail of different objects, it becomes very simple to string them together by also collecting photos looking from (and walking from) one object to the next (some of which you've done in this synth).

Thank you so much for all your comments, Nathanael. I don't know how long you've been doing this, but it's impressive to be so patient and thorough with a newbie after all this time.

My goal originally was just to do a 360 of S Mountain itself. While I was hiking up the back side of it, though, I discovered these interesting objects (the water tower and the colorful tree) and felt compelled to try those as well. I think I'll just forget about the tree for now, although I saw a great example that somebody did of a similar object, so maybe I'll come back to it later. I do want to try to get a better synth of the mountain itself, though, and to zoom from the mountain to the building at the top.

I tried to geoalign it, but the pictures didn't link well enough for me to tell which way was which.

Thanks again! Many more to come from TheBlakeE. :)