VisualSFM: Pros and Cons

Image

I’ve been working with Photogrammetry for some years now, and although I use a great variety of programs to edit the 3D models, from Mehslab to Blender, when it comes to the actual creation of the models I have only ever used 123D Catch. This is partially due to the fact I now feel very comfortable using this program, having learnt what it requires and how to achieve the perfect model, but also due to great quality and simplicity that 123D Catch offers.

Only recently have I ventured out of my comfort zone to explore other Photogrammetry programs, to see if any can compare or even replace 123D Catch.

I had a spell with Agisoft Photoscan, with interesting but limited results, so now I have turned my attention to another piece of freeware called VisualSFM. At present I have only tried out a few things, so my opinions will certainly change in the future, but here are the pros and cons I have found up to now (compared to 123D Catch):

PROS

  • It’s multiplatform: only a few weeks ago another user commented on one of my posts asking me for alternatives to 123D Catch as he couldn’t use it on his Mac. VisualSFM is not restricted to Windows/Ipad App, but supports all major systems, making it a great tool for all those that don’t have a PC but still want to try out Photogrammetry.
  • It allows control of the process: one of the good things of 123D Catch is that it is easy to use, but this is to the expense of more expert users. Uploading images and getting results with a single click is great, but it’s difficult to understand what is actually happening in between. VisualSFM instead guides you through all the steps, so if anything goes wrong you can pinpoint the problem, or you can understand which photos are better for research purposes.

Image

  • It works offline: many times I have found myself slowed down by a weak internet connection. With VisualSFM this is not necessary, which also means I can create models on site without the need of Wifi. Makes the whole process more efficient and means I spend less of my free time working on models.
  • The camera placement is more accurate: this one is still in testing, but up to now I have had no problems with cameras being placed in locations they are not meant to be in. With 123D Catch often a single photo stitches to the wrong place and causes the entire model to malfunction. With VisualSFM this doesn’t appear to be the case.

CONS

  • Less points: I compared a few models made with the same photographs by the two programs. The results suggest that VIsualSFM points may be placed more accurately, there is far less of them, making the overall model itself less accurate. In the pictures top is VisualSFM, bottom is 123D Catch.

Image

Image

  • Still haven’t finished a model: once the point cloud is created, VisualSFM has finished its job and it becomes Meshlab’s responsibility to actually recreate the surfaces and reattach the textures. Up to now I have not managed to do this. I’ve talked about Meshlab before, but in short it crashes and malfunctions all the time. It took me days to recreate the surface the first time as the program refused to do it, and attaching the texture is still something I can’t seem to manage.
  • Needs user control: with 123D Catch you can leave the program running and return to a finished product. With VisualSFM you have to constantly interact with the program, meaning you can’t multitask.

Overall, it’s got potential. It’s not going to replace 123D Catch any time soon, but I am still going to try different things out to see how it reacts and find any advantages. For a full description of how to create models using VisualSFM visit here: http://www.academia.edu/3649828/Generating_a_Photogrammetric_model_using_VisualSFM_and_post-processing_with_Meshlab

Image