rendered acad models to photoshop

[loff]

Im having difficulty finding tutorials on importing rendered acad models into photoshop (to create a montage). its easy to get the model there, and manipulate the pshop layer, but ive no idea on how to get the right perspective so the model will sit properly in the pshop image, for example a proposed extension for an existing building as an acad model imported into a photo of the existing building and surrounds. Im searching for a tutorial that can show me how to get scale, position and most importantly perspective right so the finished result looks as natural as possible. If anyone could point me in the right direction this would be much appreciated.
thanks
loff

[fuccaro]

Make the montage in photoshop whiteout the buildings. No details are needed at this step. Save the image in bmp format, and import it in autocad. Place your models over the image and put them in right position. Delete the background and render your models. You think it will work? No? Sorry, it was just an opinion.

[CADTutor]

loff

This is the kind of stuff I do all the time. You can get very accurate results but you do need to plan ahead.

The first thing you must do is to know exactly where the photograph was taken in relation to the new building - without this information you can forget it. That way you can build a 3D model of the new buildings and existing buildings or known features that can act as control points and fix the camera position in the same model. You can then use DVIEW to construct a perspective from the camera position.

Plot this perspective to EPS and open in Photoshop. Drag the EPS layer over the photograph and use the existing buildings to scale and position the EPS template. When they match, you will have an accurate outline for the new buildings.

That's it in a nutshell. Hope it helps.

[CADTutor]

Here's an example of my work. In this case, the camera position was surveyed to give an accurate fix. I also had very accurate information on the position of the electricity pylons so these were used as the control objects in this photomontage.

http://www.cadimage.net/cadtutor/Slyfield-EfW-1a.jpg
Existing

http://www.cadimage.net/cadtutor/Slyfield-EfW-1b.jpg
Proposed

The technique is relatively straightforward but to get accurate results, you need accurate data.

[loff]

Thanks for the replys. I suspected that knowing the position of the camera shot might be the key to it all. Are there any tutorials kicking around giving the lowdown on EPS? Its something i havent used before - generally i have just saved rendered model images in acad as TIFF files then taken it from there in photoshop. What are the advantages of EPS in this kind of exercise?
thanks again
loff

[CADTutor]

There's a fantastic tutorial on the main CADTutor web site that covers moving from AutoCAD to Photoshop via EPS. Find it here:

http://www.cadtutor.net/acad/acad2ki/atop/atop.html

[Mr T]

Type 3do and right click and use PERSPECTIVE projection, this may help.

You can also render with a background image remember

Nick

Design & Technology Teacher,
Grangemouth High,
Scotland.
www.autocadzone.com

[CADTutor]

Type 3do and right click and use PERSPECTIVE projection, this may help.

The 3D Orbit command cannot be used to construct accurate perspectives from known locations. For this you must use the DVIEW command. It's not as nice and pretty as 3D Orbit but it IS the right tool for the job.

[loff]

one more possibly stupid question - when noting the location of the spot from where the original photo is taken, how will zoom settings on the camera affect perspective if at all? (im no photography expert). eg, if you zoom to closeup, wont this theoretically change the location of the shot?
loff

[CADTutor]

The zoom factor or the focal length you set within DVIEW does not affect the position of the camera. Effectively, when you set up a DVIEW perspective using the POints option, you define a line of sight from the camera to the target point. You can use the Distance option to move the camera backwards or forwards along the line of sight but if you accept the default value for Distance, this will give the calculated distance between the two selected points i.e. the distance you want. Changing the focal length with the Zoom option is the equivalent of standing in one position with a camera and using a zoom lens to zoom in (telephoto) or zoom out (wide angle).

You may find this tutorial helpful in setting up accurate perspectives using DVIEW: http://www.cadtutor.net/acad/acadr14/perspect/perspect.html

This is a R14 tutorial but DVIEW has not changed since then.

DVIEW is not the easiest of commands to work with and I once wrote a LISP routine to automate this whole process. Must root it out sometime...