johnnyrex
Junior Member Rank 1
What has happened with common sense?
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Post by johnnyrex on May 3, 2020 16:35:22 GMT 5
 How accurate is it if we directly measure the size of bone, such as the total length of the femur above, by using the 10cm scale next to it? I think it is very unreliable to measure any bones from pictures because of the angle distortion. If the bone is two-dimensional, then maybe we can get the real measurements but the problem is any bone, including the femur, is three dimensional. So we will get an exaggerated measurements of bones by three or four inches. Thoughts? |
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Post by theropod on May 3, 2020 16:49:57 GMT 5
That really depends on the picture, the accuracy of the scalebar and the geometry of the specimen.
Measuring something in an orthographic screenshot of a 3D model is no problem for example, it may even be more accurate than measuring the physical object itself.
Measuring something like that regular photograph of a femur with a scale bar next to it should always at best be a plan B to using an actual reported measurement. The scale bar is not primarily there to replace reporting actual measurements, and obviously it will never be able to do that as long as that photograph isn’t an orthographic projection.
However we should keep in mind that even direct measurements need to be taken with a grain of salt. There is a margin of error there too, as you can see when you look for different authors’ measurements of the same bones of the same specimens. Large bones are tricky to measure directly, ever tried finding a pair of 2 m calipers to measure a sauropod femur with? Landmarks may be hard to discern, or authors may measure in different ways even between the same landmarks (e.g. parallel to the bone shaft vs point to point vs along the surface with a tape measure).
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johnnyrex
Junior Member Rank 1
What has happened with common sense?
Posts: 14
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Post by johnnyrex on May 3, 2020 17:34:52 GMT 5
That really depends on the picture, the accuracy of the scalebar and the geometry of the specimen. Measuring something in an orthographic screenshot of a 3D model is no problem for example, it may even be more accurate than measuring the physical object itself. Measuring something like that regular photograph of a femur with a scale bar next to it should always at best be a plan B to using an actual reported measurement. The scale bar is not primarily there to replace reporting actual measurements, and obviously it will never be able to do that as long as that photograph isn’t an orthographic projection. However we should keep in mind that even direct measurements need to be taken with a grain of salt. There is a margin of error there too, as you can see when you look for different authors’ measurements of the same bones of the same specimens. Large bones are tricky to measure directly, ever tried finding a pair of 2 m calipers to measure a sauropod femur with? Landmarks may be hard to discern, or authors may measure in different ways even between the same landmarks (e.g. parallel to the bone shaft vs point to point vs along the surface with a tape measure). That's why I think instead of taking measurements from the picture alone, it is better to manually measure the total length or circumference of the femur by using measuring tape or any measuring tools. I believe if we're using the picture of the femur with 10cm scale next to it, it will give us exaggerated results. Btw the femur belong to a tyrannosaurus specimen MOR 1125 aka B-rex. However, I do agree even when it comes to manual measurements different authors may measure bones in different ways. |
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Post by theropod on May 3, 2020 17:54:05 GMT 5
Well I can assure you if we have the ability to measure real bones, we will certainly do so instead of using a photo, but that’s not always an option for obvious reasons.
Even so, to use the T. rex in question, there are at least two different measurements of that specimen that differ quite a bit, one is 107 cm and one is 115 cm.
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johnnyrex
Junior Member Rank 1
What has happened with common sense?
Posts: 14
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Post by johnnyrex on May 3, 2020 18:05:14 GMT 5
Well I can assure you if we have the ability to measure real bones, we will certainly do so instead of using a photo, but that’s not always an option for obvious reasons. Even so, to use the T. rex in question, there are at least two different measurements of that specimen that differ quite a bit, one is 107 cm and one is 115 cm. The 107 cm comes from the original source while the 115 cm comes from The Tyrant Lizard book if I recalled. I think the original measurement is the correct one, because I got the 115 cm figure too when I measured the femur directly from the picture by using the 10 cm scale which I think is inaccurate. |
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Post by theropod on May 3, 2020 19:25:13 GMT 5
Actually both are from chapters printed in "The Tyrant King", 115 cm is from Larsson’s chapter on morphometrics whereas 107 is from Schweitzer et al.’s chapter on medullary bone. Saying a measurement is inaccurate because it is the same thing you got from measuring the femur in a picture is faulty logic, if anything that is an argumen for the accuracy of the figure. Has it ocurred to you that that figure could even have been scaled so that the length measurement is correct?
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johnnyrex
Junior Member Rank 1
What has happened with common sense?
Posts: 14
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Post by johnnyrex on May 3, 2020 19:28:17 GMT 5
Actually both are from chapters printed in "The Tyrant King", 115 cm is from Larsson’s chapter on morphometrics whereas 107 is from Schweitzer et al.’s chapter on medullary bone. Saying a measurement is inaccurate because it is the same thing you got from measuring the femur in a picture is faulty logic, if anything that is an argumen for the accuracy of the figure. Has it ocurred to you that that figure could even have been scaled so that the length measurement is correct? Well both contradicting measurements are in the same book which I think is pretty confusing. Are you saying both is correct? Or 115 cm is the correct measurement? Why? You need to take cautions because the femur is three-dimensional and the 10 cm scale is very flat compared to the femur. Have you ever seen photos of tiger and lion skulls with the same scale next to it? If you try to measure the skulls directly from the picture using the scale next to it, it will seems like we already got a record size skull but when it was measured in person by using a tape measure or calipers, the result is we got a pretty average sized specimen. |
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johnnyrex
Junior Member Rank 1
What has happened with common sense?
Posts: 14
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Post by johnnyrex on May 3, 2020 19:36:28 GMT 5
They put the scale flat on the ground, so that will caused the measurements, if we're going to take the measurements from the picture, to be exaggerated. Anyway, I've emailed Dr. Thomas Holtz about this matter and he agreed that the photo angle distortion will exaggerated the measurements. /s3/tark/images/NH/200704/14/630561.jpg) |
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