Accuracy of 123D Catch

I always go on about how Photogrammetry should be used to record everything from small finds to entire sites, but just how accurate are these models? Are they good enough only for recording the objects as nice images or can they actually be used to gain more archaeological information? In essence, is it technology for technology’s sake or is there more to it?

In order to answer this I photographed three different objects and made models out of them. I then proceeded to measure the objects, and by using a set distance in Meshlab I then measured the same distances in the models. Finally I compared the two sets of data in order to see what the results suggested.

Image

Here are the results:

Iron Buckle

Pot Fragment

Arrow Head

Object

 Model

Object

Model

Object

Model

80*

80

74*

74

76*

76

49

49

61

61

81

80

49

50

86

86

54

54

25

26

81

82

63

63

34

34.5

72

73

64

64

33

33

Error

0.6%

Error

0.6%

78

79

Error

1%

The asterisk indicates the measurement I used as a reference and all the numbers are in mm.

Overall the results suggest a maximum error of 1%, which considering the size of the objects is more than acceptable. With this data it seems that analysis of the surfaces can be done without false results appearing, and as such it does seem like Photogrammetry can have many more uses than simply pretty pictures.

A more careful analysis of accuracy on a larger scale has still to be done, although Chandler and Fryer (2011) may be of some help: http://homepages.lboro.ac.uk/~cvjhc/otherfiles/accuracy%20of%20123dcatch.htm

Still, the results seem to greatly favour this technology for the purpose of archaeological recording.

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About Rob Barratt

Mphil in Archaeological Research at Cambridge Univerity, BA in archaeology from Cardiff University, field archaeologist, technology enthusiast and computer geek. I like writing codes and making fancy models of old stuff.

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