Co-ordinates & Camera Views

[davidgarethjennings]

We are currently working on a number of projects where we are rendering 3D Revit views, and exporting them as images where the Revit renderings are photomontaged with digital photos taken at the site for which we have GPS co-ordinates of from the camera.

We would like to be able to specify the Revit 3D view camera location parametrically so that the digital photo and the Revit 3D view match each other. Does anybody out there know if there is there a way of achieving this using an offset from the Project Location Setting, or does the conversion between GPS latitude and longitude not transfer into linear dimensions within Revit? Even if the GPS co-ordinates (DMS for latitude and longitude) could be transferred into linear co-ordinates (i.e. meters), could a camera be positioned using distance parameters?

Any info would be great.

Thanks, Dave.

[aaronrumple]

We are currently working on a number of projects where we are rendering 3D Revit views, and exporting them as images where the Revit renderings are photomontaged with digital photos taken at the site for which we have GPS co-ordinates of from the camera.


I'm guessing the GPS data doesn't include, direction camera was pointed, inclination, and rotation from vertical and lens focal length? If not - matching up the camera in Revit with the image will still be difficult. Revit doesn't use a true camera for its perspective. It uses more of a traditional 3 point perspective projection system without lens curvature and other camera specific distortions. Also Revit’s shift is something that most cameras don't do (or they do it in a different way.)

You'll have better luck in 3DS Max which has a camera matching utility built in. You don't even need the GPS of the camera. Just some known distances in the picture (min. 5 point - the more the more accurate.) These can be points on existing structures of a known size. The cameras in Max are more closely associated to real world cameras.

Getting the points that you are looking for isn't too tough. You just need to understand the shared coordinated system (different in 2009 and 2010) and how to place some lines or objects at a relative position to those points using spot coordinates.

[cliff collins]

See attached PDF from an (old) expanation of the Revit Camera.

This may not speak directly to your camera-matching question,
but I found it useful in understanding how the Revit camera is designed.

As Aaron stated, Revit is not too good at precise camera-matching to coordinates
or points in a photograph--and 3dsMax would be a much better choice, as it has built-in
purpose-driven tools for that.

cheers........

[patricks]

Through much math and trig calculations, and using that Revit Camera PDF attached above, I figured out the frame size and aspect ratio of the Revit camera that matches my Nikon D70s digital SLR using the 18-70 kit lens, when zoomed all the way out to 18mm. You have to take into account the camera sensor's crop factor to figure this out. On most Nikon DSLR's that do not have a full-frame sensor (only the highest end models do), the crop factor is about 1.5. This means that the default 38.6mm focal length mentioned in the PDF would be about 25mm on a Nikon entry or mid-level DSLR.

So when I'm out on a site shooting pics for the express purpose of doing a photo-montage, I note where I'm standing on a site plan, and use the elevation information of that point from the site survey. Then I determine how far below finished floor that point is, then come up 5' - 6" (my approximate eye height), and also approximate the target position and elevation height by drawing diagonal lines from each corner of the photo.

After the view is created, I change the default 6 x 4.5" frame size to 8.56" x 5.63" (changing the field of view to match the Nikon 3 x 2 image output ratio at the 18mm focal length), then change the image size to 10.027" x 6.667" (same aspect as the 8.56" size, but now matches the 3008x2000 image size @ 300dpi that my camera creates).

Finally I drag the site photo onto a sheet in Revit, change the photo to the same size (10.027x6.667"), and then plop the 3D view down on top of the image in a sheet view. Then I can fine-tune the camera position to get it just right.

Now the view is ready to render, export as a PNG, and place directly over that same image in Photoshop.

*edit* Note that if I'm doing this same process for an image my boss took with his Canon DSLR, the calculations are difference, since his camera has about a 1.6 crop factor.

[cliff collins]

Nice response, Patricks!

Sounds like a LOT of work to get that result, though.

Still prefer the 3dsMax method which is much easier and probably more accurate.

But nice job of explaining your workflow--have any examples?

cheers.....

[davidgarethjennings]

I'm guessing the GPS data doesn't include, direction camera was pointed, inclination, and rotation from vertical and lens focal length?

That's correct, so even with the GPS it will require a methodology that patricks has mentioned:


So when I'm out on a site shooting pics for the express purpose of doing a photo-montage, I note where I'm standing on a site plan, and use the elevation information of that point from the site survey. Then I determine how far below finished floor that point is, then come up 5' - 6" (my approximate eye height), and also approximate the target position and elevation height by drawing diagonal lines from each corner of the photo.

Thanks for the PDF cliff. I find that with Revit, knowing how things are computed within the program can help enormously. I do agree that 3D studio max is probably a better tool for the job, but as always I´m wanting to push Revit to its limits!

[patricks]

But nice job of explaining your workflow--have any examples?

cheers.....

Sure do :)

First couple are a historic church renovation and addition. The tower at the top of the first pic was rendered in Revit. It was destroyed several decades ago and we're going to restore it. The buildings in the background are the additions. Second pic is from the other end of the street.

Next one is a rendering of a new nursing education facility at a local community college.

Last one is a local bank, which I think came out quite well in the landscape and making it look like it's really there.

[cliff collins]

Patricks,

Your method works very well. Thanks for posting.

Good to see very convincing photo-montages are possible in Revit
with Photoshop.

Applause applause!!!!!!!!!!!

cheers........