View Full Version : Overlay drawing - perspective helpers

12-07-2009, 06:05 AM
I'm working on a project which requires some fairly complex camera matching (still photographs), here's how I'm tackling it:

I've got an acetate sheet taped to my monitor which I'm using to trace landmarks, road lines and any buildings which I need to line up with inside Layout. I can then reveal the geometry and use the lines I have drawn to get the correct camera angle and position for the background image.

What I'd like to suggest is a way to draw simple lines as an overlay which will always remain on top of the Layout viewport. It would be even better if it is possible to have multiple overlays and have them be keyframed so that you can work with multiple images in each scene.

All that would be needed is a simple pen tool, perhaps a bezier option and maybe a text tool.

12-07-2009, 10:20 PM
Very easy to do.

1. Display Options - Backdrop. Load your background image for your montage (you should already get this to the exact proportions & also get rid of any lens distortion with Ptools or similar. For example it is surprising just how much distortion there is on a 24 mm zoom. This can play havoc when trying to line things up, so get rid of it lens distortion)

2. Create a new Object & trace all the key things, like roof ridges , power poles, surrounding building, existing site building is really helpful as well.

3. In Layout scale it done to 1% & Parent this to the camera only a few centimetres away on the Z axis.

4. Parent the background image to the camera as well. But fine tune the distance (for scale) later. Adjust the angle of the LW camera to the field of view you are after & move the Outline object on the Z axis to fill the field of view. (It is easier to decide a Width & Height ratio at the beginning of the job based on the Background image you will use, & then stick with it)

5. Forgot to mention earlier, As well as building you site model, build simple structures for the surrounding buildings, power poles, gutters etc for lining up with the Outline object which will be sitting in front of the camera (your virtual piece of acetate).

6. Doing it this way enables you to line things up more easily. (I have also found many errors in architectural drawings this way, firstly believing I am stuffing something up, only to find out that I have been going around in circles because the drawings are stuffed).

7. If you set it up this way with all the scales & positioning correctly, as the bastards keep changing things its a piece of cake to do another render & drop it into Photoshop very easily. The thing is you can get a really accurate position so you donít need to cut out more things than necessary for the Photoshop foreground layer.

Its also great for those transparent & semitransparent (alpha channel) areas because when you have lined it up in LW & it will be exactly the same in Photoshop.

8. Its sometimes easier to put a Null in the centre position of the scene & parent the camera to this & swing the camera around via the Null. Last issue, but actually the first, when you take the photograph for the background use a tape measure & measure the position of the camera from a known point, Also keep the camera absolutely level. You will be minimising variables. If the camera doesnít point up high enough take a second photo.

12-08-2009, 01:19 AM
The scene (stripped down) with the above comments. Hope it makes things clearer.

12-10-2009, 02:43 PM
Thanks Jon for the indepth explaination!
Makes it much easier for everyone to understand. :thumbsup:

12-19-2009, 12:19 AM
In the ‘Old” days if you were taking a background image of a tall building & you were using a 5x4 large format camera. You would keep everything horizontal & just shift the lens up or the back plate down so you would see the top of the building (they still do & there are some very nice lenses for 5x4). Then it won’t appear that the building is falling over because you wouldn’t have had to tilt the camera up a few degrees. (or use a shift lens http://www.the-digital-picture.com/Reviews/Canon-TS-E-24mm-f-3.5-L-II-Tilt-Shift-Lens-Review.aspx to do the same thing)

The best thing to do these days, if you don’t have a shift lens at hand..... Because the pixel count on cameras is large enough & you can easily increase it by 10% if you use RAW, & in a lot of respects the image will look better for it with careful sharpening, is to use a wider angle lens so the whole subject fits in the image, & then crop the bottom of the image.

Keep the camera horizontal (get a spirit level http://www.amazon.co.uk/Hama-5411-Camera-Spirit-Level/dp/B00005QFAF or a builders level http://www.nextag.com/builders-level/stores-html for more accurate level over greater distance) It’s worth spending the time & getting the camera exactly level.

When lining up your background image for a montage. Its just makes life so much easier to have a level camera. & on top of that I find it a lot less work to get it right in the camera than to bugger around on the computer.

& finally, get rid of lens distortion.