photo matching to a shift lense

[seamus]

I'm in the process of trying to match a 3d model to a picture taken by a shift lense. I have exact positions for the camera location and known control points and the lense is 45mm. I have placed the picture as a backdrop to the camera view port and I can change the position of the camera target until the control points match where the need to be. Unfortunatly I cant seem to get an accurate match using max's camera. I have used this method with success using standard lenses. i use a shift lense because i want to keep the verticals in the pictures. I know i can use the 2 point perspective camera in max, but the matches need to be very accurate - exact infact and the 2 point method requires guessing.

Has anyone any ideas - is trying to accurately match model to a pic taken with a shift lense a waste of time??

[Jeff Mottle]

The trick to get verticals vertical in max without a camera correction modifier is to make sure your camera target is in the same vertcial plane (same Z) as your camera. Then you need to add some pixels to the bottom of your canvas (photograph) until the horizon line is in the middle of the image.

 

I've not tried it, but in theory you should be able to use the camera correction modifier with these steps:

 

1. set the camera to the proper height (your photographer should note this)

2. set the camera target to roughly the elevation that the photographer used

3. Set the camera target to the proper direction. If possible you should ask your photographer to mark on the final image where the horizonal center of the frame was when they took the picture. Vertical too for that matter.

4. Apply the camera correct modifier until the survey points you have in your scene line up with the image.

 

Oh one more thing, you should make sure you get the original negative and get it drum scanned. If you get a digital that was cropped in any way the FOV that you have is useless.

[seamus]

Thanks Jeff.

Will try those steps - the results need to be very accurate. I'm using renderdrive to render my scenes so I use the renderdrive software light which doesnt work with the camera modifier. How can you ensure that the target and camera are at exactly the same z when taking the photo? Do you know of any sites/books outlining precise photo-montage methodology?

[Jeff Mottle]

Thanks Jeff.

How can you ensure that the target and camera are at exactly the same z when taking the photo?

That's why you need to add pixels to the bottom of your image so that the horizon is in the center of the image. If the camera target and camera in the real world were at the same z level you would not need to use a shift lens. Verticals only become non-vertical when you add perspective to the view.

[Ernest Burden III]

How can you ensure that the target and camera are at exactly the same z when taking the photo?

 

It's mostly by eye, but you can do several things.

 

In my 35mm film camera I have a gridded focus screen. You can buy them at a pro camera store. As you swing the camera up and down it is extremely obvious when you have building verticals lined up with the grid (most buildings, anyway). For a digital I would think you could put a thin clear tape over the LCD and scratch lines in with a pushpin or draw them with a technical pen (having the camera somehow held in place in a way that you could use a triangle as a 'set-square'. That assumes your screen has a hard plastic surface--mine does. I just thought of this as I wrote it.

 

My old trick was to rotate around as I was framing the picture to try to find my reflection in a pane of vertical glass. If you set the center of your shot on your reflected camera lens it will be a horizontal shot. Just see how the scene is framed top/bottom and carefully frame the shot without changing the tilt--a vertical shot.

 

In the 'puter you just set the Z height and target Z to the same number, or check the camera rotation to be 0 degrees.

 

You can also correct the keystoning of either a scanned photo OR a digital render in Photoshop, but at the cost of some clarity (pixel death).

[Sketchrender]

Seamus

How are you, hope all is well in Limerick.

 

You were asking if there was any litrature available in relation to corrective photography in the Visualisation field.

I came across a page on the http://www.hayesdavidson.com/

webiste which has a publications section, and there they have a ducument they wrote called ACURATE.

It is for the exact purpose that you want if you read the breakdown they give, basically the rules to follow in order to sadisfiy the planning bodies requirements in London, but the basic facts and procedures will be the same for ireland.

 

Now, the website is down as I write this, so maybe that is just for the moment, but I wrote to them a few months ago and they say it is available on request but not for sale.

I wrote but never got an answer.

If you have any luck please let me know.

You know my email address.

 

Talk to you soon.

 

philip kelly

[Sketchrender]

Just got in to the website and here is the page I was talking about.

 

http://www.hayesdavidson.com/html/publications/publications.html

 

I think I will give thema ring tomorrow, and ask them what's the story about getting a copy.

 

phil

[seamus]

Thanks Phillip

Have that book - doesn't get into the technical side of things though. We have nailed down the process using a standard 50mm lense its just that I need to get a fool proof process for using the shift lense.

Seamus