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Old Jul 08, 2012, 05:11 AM
bat
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Help!
Technical question from an archaeological dig in Israel

My friend and I are supervisors of two seperate dig areas at Tel Dan this summer. This past week a professional came to do some technical drawing of top plans using a Total Station in my friends area. So that he could remove a wall and continue to the next stratum. Unfortunately not all the work needed was completed. I am working with my friend using a canon 10-22 mm lens on a 4 meter pole to take verticle photos to aid in drawing. we quickly found the photos do not perfectly line up with the previous years plans made with a total station.
If I align the left wall with the top plan the right side of the image does not align well and vice a versa. I assume this is due to lens curvature. I have Photoshop cs4 anyone know of a way I could use my equipment to make accurate drawings that match up with the previous years plan?
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Old Jul 08, 2012, 01:13 PM
Ascended Master
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The two images; the photo and the drawring are taken with different focal length lenses, or at different altitudes for the camera.
Photoshop should permit scaling one to the other.
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Old Jul 08, 2012, 03:50 PM
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Hi,
Universities here in the UK have developed software to work with aerial photos.
They can even "drape" the photo over the surveyed heights of the site.

I have seen the results but don't know who is doing it. I would think that universities and professional archaeologists in your country will also have some very good software.

Hope that helps.
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Old Jul 08, 2012, 03:58 PM
Ascended Master
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For such work, there must be a known dimension, like a meter stick to permit adjusting image sizes to fit.
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Old Jul 08, 2012, 04:39 PM
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Quote:
Originally Posted by Sparky Paul View Post
For such work, there must be a known dimension, like a meter stick to permit adjusting image sizes to fit.
I assume that's it on the left hand side.
If this was conducted properly then the original survey measurements should be available and they would be used, in conjunction with the meter stick that is visible to scale everything correctly.

I am in the process of taking aerial photos of archaeological sites that have recently been surveyed. The teams doing the surveys left 2 base pegs in situ. The base pegs were what they attached the base line to in order to make their drawings from measurements using the base line. The pegs positions were accurately located using GPS (an expensive GPS system).

When I turn up I highlight the position of the base pegs so the base line can be put onto the photos. I take along my own 2 meter measuring rod so scale can be
established as it is easily visible in my aerial photos.

Aerial photos may not be exactly vertical, archaeologists have developed software to correct the photo so that it then gives the correct dimensions without the distortion induced by being off vertical.
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Old Jul 09, 2012, 06:54 AM
bat
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Thanks Sparky,
actually the guy with the total station is returning tomorrow to finish the drawings so our efforts were not neccessary. I am aware that there are various photogametry and survey based programs that can be used with aerial photos to get excellent results, but those programs are beyond the budget of the current excavation. In our photo we used a 1 meter scale and I was able to size the photo to match the scale of the drawing. we also had several mesurments that we made of specific rocks so we had secure spatial references. However using photoshop to tilt/warp/flex/ bow or whatever else is needed to make the photo match the spatial references and previous drawing is a bit beyond my knowledge base. I'd love to take a class down the road that would teach me how to do technical survey drawing from aerial photos.

Thanks for the help. I plan to learn more on this subject down the road.
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Old Jul 09, 2012, 10:14 AM
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Hi bat,
Good luck with the project.
I can't do anything but basic stuff with photos. I use the free software programme the GIMP which was originally developed for Linux but now is available for Windows.

The photos I took were for professional archaeologists and they had access to the universities and the software. I seem to have raised quite a bit of interest here and have had some very nice comments on my results.

I do the aerial photos for no charge apart from my fuel costs. That way there are no complications and I am my own boss ! Being retired helps as I have the time and enjoy doing it. The professionals survey the sites, do the drawings and then leave a couple of base pegs in. I then turn up when the weather is suitable and have the site to myself.

Most of the sites are in stunning scenery so I get to fly, have a picnic with my wife and do something useful at the same time.
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Old Jul 09, 2012, 10:14 AM
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I was thinking that aligning the meter stick with North would be useful also as an aid to establishing orientation at a site.
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Old Jul 09, 2012, 11:43 PM
Happy on 72
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Bat,
This may or may not help you at this time but you may be interested in checking out DXOptics Pro. The software automatically corrects lens distortion and it also lets you force horizontal and vertical lines. I'm not sure if this will help you at this time but it does come in handy.

Mike
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Old Jul 10, 2012, 07:46 AM
Predictive text is for aunts!
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Have a look at Kite Aerial Photography

Hi Bat,
This is also being discussed in the KAP forums, where there are some awesomely knowledgeable folk chipping in.

The biggest forum is http://arch.ced.berkeley.edu/kap/discuss/
which may be of interest.

Hope this helps.
Regards
Andy
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Old Jul 10, 2012, 09:13 AM
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Quote:
Originally Posted by Sparky Paul View Post
I was thinking that aligning the meter stick with North would be useful also as an aid to establishing orientation at a site.
I do that. Not really necessary though as the site surveys are originally done with a very accurate GPS system.
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Old Jul 10, 2012, 10:01 AM
bat
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Sparklet,
as it is I Have the meter stick running north south
great mins think alike

Andy thanks for the link I'll check it out tomorrow
Got go
Tommy
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Old Jul 10, 2012, 04:13 PM
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I see at least three distinct potential problems using AP for mapping things:

- Distortions created by the focal of the lens
- Distortions created by paralax and misalignement
- Distortions created for not having perfectly vertical views

Any of these distortions can be corrected with Photoshop as long as you prealably disposed a physical grid (let say IDEALLY a visible rope network with 1m square divisions) on top of your aimed subject. Once you got a well known quadrangular object on your initial photo documents it will be much easier to tile and allign your final picture and to correct it with the proper Photoshop tools. (And yes, there are more than one in Photoshop )
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Old Jul 11, 2012, 10:53 AM
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Most people doing AP don't need that sort of accuracy.
For those who do then specialist software has been developed.

For archaeological purposes the site would first have been mapped out by hand.
A grid system would be used for recording everything while working from a known baseline.
Aerial photos would be a bonus to the archaeologists and they already have the means of correcting them and they also have the accurate drawings to compare against.

Aerial photos can also include a large area around a site and show how the site "sits" in relation to it's surroundings and other areas of interest.

The photos are a nice addition to have but the important dimensions and placement have already been done and accurately drawn.
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