How can the command MATCHPERPECTIVE be used ?

Sakko

Hi all,
i am trying to figure out how the MATCHPERPECTIVE command is functioning !
I read in the Help that the command matches the current model space perspective view
with a background image by selecting 3 or more matching point pairs.....
Following questions are arising :
1. What is meant by background image ?
Is this an image file attached with the IMAGEATTACH command ?
2. In which plane in model space should the image be placed XY , YZ, XZ ...?
3. What should be the scale of the image ?
3. If the command is functioning in perspective mode then the attached background
foto, which is already a perspective view of the building,
is also perspectively displayed in model space during the point mapping process ?? !!!

I don't get it done!
So i am attaching a 3D model and a foto of the real house (place dwg and image in the same directory
for the image to be find !!)
Could one possibly figure out how to proceed and produce a usable perspective match of 3d Model and Foto ?
Thanks, Regards
Konstantin

Tom Foster

Very good questions. Haven't tried this invaluable tool (the first such in the native-dwg world AFAIK) myself yet but would love to hear some expert and practical guidance.

A great building!

Hans De Backer

Q1. What is meant by background image ?
Is this an image file attached with the IMAGEATTACH command ?

No, please use the (new in V17) BACKGROUND command to set the background for the current view.
Choose the Image option and select MatchPer_Image.jpg.

Update: see my post below - at the moment of this post, the BACKGROUND command is not yet available in public releases, so instead please create a view, select it in the View Explorer and click on the '...' browse button of the Background field to set the Background properties of the View.

Q2. In which plane in model space should the image be placed XY , YZ, XZ ...?

The image is used as a background for the view, and does not move with the model: you will notice that you can pan and zoom the model (also during the Matchperspective command) without the background being modified.

Q3. What should be the scale of the image ?

To make most of this example photograph fit on my screen, I scaled it by a factor 0.8

Q4. If the command is functioning in perspective mode then the attached background
foto, which is already a perspective view of the building,
is also perspectively displayed in model space during the point mapping process ?? !!!

Yes, that would be a tough one to crack.
Hmm, it is actually what we initially tried: allow to IMAGEATTACH photos at any preferred location in the model, and then match the model with a photo using the same point-matching approach, until the developers explained and convinced us that it could not be done.
So instead, for each photo you want to use as the background for a rendering, create a dedicated view with that photo as the background, and match the perspective of the model with the one from the photo.
Mind that for various reasons the result will not be 'perfect', but still very useful: I attached a sample using your drawing.

During the matchperspective command, I recommend to use an X-ray visual style, so you can simultaneously see your background and your model. If the model gets in the way, pan it out of your way, you will notice that the already matched point pairs nicely will move along as you pan.

While matching the attached example, I had a bit of trouble to find good match points for the bottom part of the building, so I made some guesses...
The attached screenshot was made during an initial attempt: it gives you an idea how the point pairs work.
There is no need to indicate so many pairs, usually a couple of points at the top and the bottom of the model should do, preferably along the vantage lines of the perspective.

Hope this gets you on your way,
Hans

Hans De Backer

Update:
the BACKGROUND command is not yet available in public releases, sorry for that, but in fact, this command just provides a shortcut to the Background properties of a view.
So create a view, select it in the View Explorer and click on the '...' browse button of the Background field to set the Background properties of the View.

While we're at it...
when creating multiple views on a model, using various backgrounds, it can be handy to add the 'View' combo control on one of your toolbars. It enables fast and easy switching between your views.
This View control can be found at the bottom of the list of 'Available Tools' on the 'Toolbars' tab of the Customize dialog ( CUI command ).

Sakko

Hello Hans,

many thanks for your detailed answers !

I could reproduce all the steps and everything functioned as described.

Just a small clarification....

In your answer to my Q1 you state :

"...use the (new in V17) BACKGROUND command to set the background for the current view.."

If run the BACKGROUND command in the command line i get the following message:

BACKGROUND
EDITGB
This command is not yet supported.

So it is important to set the Background Property of a perspective View in the Drawing Explorer
and in the Edit Property Grid of the View to set its background Image.
I have attached a Screenshot for all users wishing to use the MATCHPERSPECTIVE command.

Best Regards
Konstantin