I’ve been playing with this ‘backdrop’ feature quite a bit since first acquiring the program only a few weeks ago. Here’s what seems to work for me …
Using the front view as an example:
To shift the backdrop on the X axis you need to add or remove pixels on its left side. I do this by loading the picture into Irfanview and selecting [Image/Add 3DC] from the menu.
To shift to the right use a positive value.
To shift to the left use a negative value.
For me, the amount to add or subtract has been guesswork, but you can do this while 3DC is running, so it’s actually quite simple. After adding or removing 3DC, resave the image then switch back to 3DC. Click the front view icon on the main toolbar to bring up the backdrop image. Make no changes to any of the settings. Click OK. The image will update automatically and you can see whether you added or subtracted enough immediately. If not, switch back to Irfanview and adjust again.
THE RED LINE SCALE DILEMNA.
If anyone can get that red scale line absolutely perfect (what is it, to 4 decimal places??) using the mouse, in that undersized dialog view then my hat’s off to you. I sure can’t. At least not with the BIG backdrop images I’ve been using.
So here’s what I’ve been doing …
First, find a good sized dimension on the plan that’s easy to replicate using a primitive in 3DC. For example, the project I’m working on at the moment has a certain horizontal dimension that measures 12ft. exactly. Since my grid is layed out in feet, and I can easily size a primitive to exactly 12ft. I chose that dimension. In the backdrop dialog I stretched the red line as close as my old eyes could get it, and made sure the starting and ending Y values were identical (to ensure a level line).
I then sized a cube to exactly 12ft wide and layed it up against the dimensioned lines in orthogonal view. Of course, it didn’t match – and yours probably won’t either. So…
Since I knew the cube was accurate, it meant the backdrop wasn’t. In order to adjust it, you need to change the length of the red scale line you dragged earlier. But DON’T use the mouse. Instead change only the END value for its length in the number box (in my case it was ‘End X’). A longer line (higher END value) makes the plan shrink proportionately, and vice versa. Don’t change any other values. Click OK.
Compare the backdrop to your primitive again. Readjust as necessary. This is trial and error to be sure, but the steps are so quick and simple, you can get it nailed in only a minute or so.
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