TurboCAD file conversion help required

[454]

Help please!

Now I know that out there are lurking Technophiles who know all there is to know about CAD.
Thankfully I am just getting into the habit of making drawings in TurboCAD & exporting the files to .dxf for the purpose of laser cutting in steel.

My question is:

Is there any way of converting a .pdf file into a .dxf file or similar to allow import into any CAD design software package? Has anybody tried to do it?

I suppose one could equally ask about .jpg  .jpeg, .bmp just as easily as .pdf.

Any suggestions would be well appreciated, thanks.

Dave
454

[Andy B]

Hi Dave,

My 2p worth:

"Is there any way of converting a .pdf file into a .dxf file or similar to allow import into any CAD design software package?"
Simply and reliably (dimensionally) - No.  With some 'faffing' and careful checking and adjustment - Yes.

I've not done it to import to CAD, but have done it for my wife's stained glass designs so that she can then quickly fill areas to try out colours.

The main issue is  that dxf files are vector files - all the elements are defined by geometric coordinates. The other file types you mention - jpg, bmp, etc - are raster files, where all the lines, points etc are just collections of pixels.

There are tools that will create 'best fit' vectors based on raster images. 'Inkscape' is one such tool, and is free!
The quality of the vectors created is, as you may guess, highly dependent on the quality and clarity (contrast) of the original raster image. Straight lines are not too bad, but it won't necessarily recognise circles / arcs as such - they will often be created as splines (with many vertices) which laser cutters don't like!
I think Inkscape can work off pdfs - would need to check at home.

There is an alternative which is possible in AutoCAD, so might also work in TurboCad:
Import your raster image (scaled) and use it as a background (on a different layer) to overlay your lines and curves.
Although it requires creating all the vector data from scratch it might still be quicker than going through a conversion routine and then having to correct / tweak many of the created vector objects.

Hope this helps for starters.

Andy

[IanT]

Hi Dave,

I've used TC for a few years now and have not really found a good solution to the problem of importing a scanned image into it (in other words converting an 'image' file to a 'vectored' drawing). Andy has given a very good summary of the problem below. I have not tried 'Inkscape' but did try a trial version of 'Sketch-up' (I think it was) a few years ago and just couldn't get usable results. Things may be much better now.

One thing that I did try (with limited success) was to import the image I wanted to copy as a background layer - and then use this to sketch over it manually (on another layer). I then used this 'sketch' layer to draw my component and dimensioning layers - having re-scaled it and tidied up various key datum lines (e.g. get them straight and running parallel to each other etc). It was a lot of work and frankly I decided that it was easier to just measure and draw the image directly.

If there was a really good programme that made this easier now - it would be extremely useful - as I could import and scale a lot of my existing 'Plans' library (from old railway magazines) currently sat in three ring binders on the shelf.

Regards,

IanT 

[454]

Thanks Andy.
I think you have answered my question & bolstered my understanding of the issues relating to this task.
Had a feeling it would not be that simple.
Now I will go away & experiment.

Just as I replied to Andy, Ian threw in an answer as well, so to both of you thank you.

Cheers & thanks
Dave
454

[454]

Update:

Just downloaded "Inkscape" & it loaded in a straightforward manner onto my Mac.
Looks quite easy to use so am having a play to see what it can do.
So far so good, looks very promising.

Dave
454

[Andy B]

Whilst on the subject, and probably going beyond Dave's initial aims but maybe of interest to others:
I have had success is using raster files in CAD in a slightly different way.
I have a Midland Railway GA drawing of a loco that has side and top views but no end views - so how to work out the size of things like the smokebox door hinge straps and the radius of the tanks?
Many photographs of the particular loco class have been published, but none are good enough straight-on views of the front to scale off directly - most are 3/4 views.
My solution:
a) Find the best photograph showing the details required and as head-on as possible and scan it
b) Use  reverse perspective correction in a tool such as GIMP (free) or Photoshop, then scale it vertically and horizontally (using known dimensions from the GA such as buffer beam width and footplate to chimney height)
c) Import as a reference layer to CAD then overlay lines to determine dimensions. In my experience, most components on rolling stock were to the nearest 1/4" on small parts and nearest inch on larger items - it surprises me just how often this method comes out with measurements that are very close to those increments.

A couple of caveats:
1) It only works on objects that are in the same plane, and
2) It is prone to variations due to lens distortion, etc
3) It can be hard to set the grid for the perspective correction unless the object has very clear edges.
You can see in the attached example that I have a reasonably good alignment with the smokebox door for setting the strap sizes and shed plate position. The tank shows more mis-alignment, but was good enough to determine that the top corner radii are 9" and the main radius 12ft.

In the end though, as no drawing exists and all the class were scrapped no-one will prove I've got it wrong too easily!

I've also used the reverse perspective correction / scaling technique to work out lettering spacing from PO wagons.

Andy

[IanT]

Very interesting Andy - I'm in the middle of something similar myself, trying to understand exactly how the Sentinel was actually built.

Fortunately, we've just acquired some new drawings that are helping considerably - but they have been photographed (not scanned on a flatbed) and there is noticeable distortion. Your technique would probably help with these too but I'm on a tight schedule - so managing with lots of photos and eye-balling (mainly using rivet 'lines' as a form of tape measure etc.)

However, I do agree about 'whole' numbers where possible. I'm working in full sized dimensions at the moment - because it is much easier to guess the actual size of something when choosing between (say) 10.86" and 11" - it's easy to guess the probable size (less so between 12.21 mm or 12.36 mm ! ). Small difference might not sound much but they can be cumulative on a larger object. I spent best part of an evening recently looking for 2" I'd 'lost'. Not very much but things that should have joined up - didn't.

Anyway Dave - I'd be very interested to hear how 'Inkscape' works out for you - I'd like to take a look at it but it will have to wait till I have a bit more available time.

Regards,

IanT

[Geoff Nicholls]

sorry if someone else has already answered this topic, I just noticed it and am about to go out

Paul Tracey, who sells turbocad put this on youtube:

https://www.youtube.com/watch?v=XbkYmU4-Zus

I tried it out, it does work. I'll try and dig out my notes over the weekend.

[Gavin_B]

Thank you Andy-B for the tip on correcting perspective.  I have struggled to do this for ages but tried it in GIMP and its so easy.

I also use inkscape for etched brass and laser cutting, takes a bit of getting used to but very powerfull