messiah

I'm pretty handy on the autocad side of things but need some help with photomanipulation.

This is what I want to do...

I need to take photographs of building's elevations, then be able to put that photo into autocad and trace it. I can do that BUT when taking a pic from from ground level and looking up, the top of the building will be leaning in on itself - if you see what i mean. Basically what I want is to get a completely flat, face on pic.

any ideas?

Bumpster

Don't think you'll be able to. How tall is the building you're photographing?

The only way you could do it yourself is to get a ladder so that you are 1/2 way up. Then take a series of photographs and splice them together. If you try and get all of the building in, in one shot then you'll have trouble with the perspective.

There is a technique (which I forget the name of - photometric survey?) where some clever people take loads of photo's digiatally and piece them together. Best thing is the whole photo they produce is to scale! But it's V V V expensive!

messiah

Well I've done something similar in autocad, so I'm assuming the same thing is possible in photoshop or whatever.

eg, say for instance you want to draw a building which is octagonal, so that if you look at one face, there will be another at each side that you'll see at an angle. You can draw them as if they were just like any other face, but then rotate them round in 3d so that you were looking at them the angle you're looking for - you can then "flatten" this image so that everything is on the same plane.

So in photoshop If I had a pic (it would need to be taken dead centre) I would need to be able to bring to the top of the pic towards me, so that the side walls appeared vertical, and then to flatten that image.

I apologise if I'm not explaining myself too well.

IWatkins

Two ways really.

One is to use a lens that allows you to adjust the lens so that the building appears square in the frame. These tilt lens are expensive so if it is a one off, I wouldn't bother.

Second is to take the picture and then transform it in Photoshop so that it appears square. You may loose some detail (depending on the original shot) but is usually good enough for visual usage. Only downside is that you cannot really use the transformed images to make photographic surveys, but it doesn't sound like you want it for this. In Photoshop you want the Transform tool and use the Perspective version.

Cheers

Ian

dosenöffner

Paintshop also has a tool for correcting perspective. Easy enough to do. All menu driven with +/- % values for perspective.The height will be the tricky part if you are looking for accuracy. If you are not overly worried about the height then draw vertical lines using the top face of the building as the cut point. All windows and doors should follow suit. Use the extend / cut function in AutoCAD.

jason4656

IW is spot on, select the area you want to manipulate, use the free transform tool to transform the perspective of the image, i am quite sure you could get some idea, but without playing with it myself i am not sure how accurate it will be.

John Catlin

Within Photoshop you can correct for converging verticals.

To put this right, select the Crop Tool and drag the crop across the image, now click the Perspective box from the Options bar and drag the corner handles around so that the edges of the marquee run parallel to the eneven verticals and the horizontals. When you apply the crop the corners will be pulled out of square, righting the distortion.

Hope this helps.