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Importing a drawing on a graph paper

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Importing a drawing on a graph paper

atharva
I'm trying to reengineer a part and made a outline of it on a graph paper. I've imported the image into LibreCAD. Is there a way to match the 1cm on the graph paper to 1cm in LibreCad? So that I can now draw the entities to match the size on the paper?

Thanks.
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Re: Importing a drawing on a graph paper

dellus
You have to scale the imported image to the needed size. Measure a known distance (easy with the graph paper) on the screen with the measuring tool (be sure to have free snap on, so that it doesn't snap to any other objects or image corners), calculate the needed factor to get to the right size and scale the image with modify - scale.
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Re: Importing a drawing on a graph paper

atharva
Thanks dellus. Can you give me exact steps? I thought there would be a way to use free snap and measure 1cm of the graph paper on screen. That should be sufficient for LibreCAD to set the scale. Apparently not that easy.

Thanks in advance.
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Re: Importing a drawing on a graph paper

dellus
You can't kind of calibrate LibreCAD to the image, you have to adjust the image to LibreCAD.
There isn't really much more to explain about the procedure. By default an image is imported with one unit per pixel. A bitmap-image doesn't really have a physical size, some carry an optional dpi-value with them. When importing the image you can set a scaling factor in advance (what is a bit useless as you only can measure and calculate after having imported), or if the image is a scanned one with a known dpi-value, set that ( can also be tricky depending on your drawing units).



When taking the measurement from the graph paper better take the largest possible distance for more accuracy, let's say 20cm. But be aware that scanners and optical lenses produce distortions, so there always will be some inaccuracy.
Now divide the distance to be ( the wanted one) by the measured distance and scale the image with that factor.
Now an important issue I have forgotten to mention is that after scaling the scaled image seems disappeared. You have to perform an "Auto-Zoom" to bring it back. This is a bug that urgently should be repaired.

Good luck and please report back if this solves the issue.



 

   
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Re: Importing a drawing on a graph paper

atharva
Thanks Dellus. Been a bit busy. Will try and report back.
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Re: Importing a drawing on a graph paper

atharva
Happy to report that this worked for me. Thanks again. Here is what I did.

1. Look up the image properties in any image software. What you are looking for is PPI or DPI.
2. Import -> Image into LibreCad and specify the DPI in the box for DPI
3. Use the measurement tool to measure a couple of distances (make sure they are at least 20-30mm for better precision)
4. If the real measurement is say 100mm and it shows 50 in LibreCad your scale factor is 2 (100/50)
5. Scale the image and specify 2 as the scaling factor.

Check a few dimensions to make sure you are within acceptable range.
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