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Thread: Raster Image Scaling

  1. #1
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    Raster Image Scaling

    I am linking in a raster image. It is all set up to be able to be imported at 100% horizontal and vertical scale. These values are not changeable. I have done the work so I could import at 100% and not need to draw lines, scale images, or jump through hoops.

    But Revit WILL NOT import it at 100%. It seems to be arbitrarily deciding what scale to bring it in depending on the view scale.

    Am I missing anything?

  2. #2
    Member willsud's Avatar
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    Well, I didn't know you could link a raster image, I thought it was imported.

    FWIW I've imported hundreds of scans of drawings into Revit and other cad packages and there was never one that was correct but had to be tweaked (and if a scanned image, it is usually stretched about 1% in the direction of the scanning head).

    I've come to the conclusion that it is impossible to rely on a scanned image within a vector cad package - but Revit does a better job than many.

    Perhaps you could explain a bit further?

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    I have a sketch. It is at a scale. I would like to import it into revit to use to create the basis for a conceptual mass. At this point I don't really mind if it's 1% off, I simply want it to import at the scale I drew it at so I can get on with things instead of needing to go through the rigamarole of drawing a reference, scaling to the reference, etc.

    Is this possible?

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    Member willsud's Avatar
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    The short answer is that, sorry, I don't know - but I have never managed it.

    Some cad systems have factors you can apply to the image so that the appearance is scaled but not the image itself and this is what I think happens in Revit using the image Properties pixel size in X and Y.

    I always use reference planes to check dimensions and then adjust the X and Y of the image appropriately to get a best fit.

    The scale you set in the view doesn't make any difference as far as I can tell.

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    That's kind of what I figured. I was hoping that I was missing something.

    Thanks!

  6. #6
    Mr. Revit OpEd
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    You may already know this bit...

    It is imprecise but yes, you can "fix" the image, using the Scale tool. It has a couple options to define how big the image should be. I focus on something that I "know" the size of, a door opening, the length of a wall, a property line length...something. The approach I use is to pick a first "point" and a second "point" and then supply the "correct" length. Revit scales the image based on the "wrong" length between points and uses the "correct" length to increase the size to match. When you use the measure tool between those same points (just pixels remember) you'll find the image is much closer to the "correct" size.



    Thought I did a video ages ago but apparently not, so I recorded a groggy one just now... HTH.
    Last edited by Steve_Stafford; March 25th, 2011 at 02:59 PM. Reason: added video link

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    Member Alex Page's Avatar
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    Revit may be scaling the image by itself - Say you are inserting a 300dpi image, 100x100 mm in size, when it comes into Revit, it will be a 72dpi image, 416x416 mm in size - so the image is exactly the same size (same number of pixels)

    So - in Revit, scale the image using the scale button and enter in "=72/300" and you get your image at 300dpi, 100x100mm (even thou Revit still reports it at 72dpi)

    So in Summary - if you know the dpi of the image coming in to Revit, its easy to match.

    On this note, if you import the image into a draughting view, be sure to have the scale of the draughting view already correct, and follow as above. this is how we (when we need to) import images of our Revit model "to scale"
    Barrie likes this.

  8. #8
    Member willsud's Avatar
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    All interesting stuff, many thanks...

    but where does Revit get 72 dpi from?

    I can see it is mentioned in the Type Properties box but is it affected by the OS screen resolution (my Win 7 64 system mentions 96 - is that ppi or dpi? )

  9. #9
    Member Alex Page's Avatar
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    No idea - but its the 72dpi in the types properties that led me down the track I explained above, and that seems to work!

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    Quote Originally Posted by willsud View Post
    All interesting stuff, many thanks...

    but where does Revit get 72 dpi from?
    It seems Microsoft uses mathematical trickery to get the software to show 96 DPI but screens are typically (I believe) designed for 72 DPI which is what one sees no matter how high the DPI of an image goes.

    http://en.wikipedia.org/wiki/Dots_pe..._DPI_standards

    Alex, I will be trying your method momentarily and if it works, mad kudos.

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