Using the correct drawing units

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sinergy
Newbie Member
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Joined: Thu Feb 26, 2015 12:54 pm

Using the correct drawing units

Post by sinergy » Fri Feb 27, 2015 5:59 pm

Hi
I am a new QCAD user an to CAD SW as well
I have some doubts on how to know what drawing unit I am using each time. I know that I can change the units in the user preferences to start with.
This doubts arises because after configuring the drawing env. to work with mm units and I draw an entity and measure it, I get a numeric value.
If I change the drawing units to inches, for example, for the same drawing and draw another line having the same "visual" lenght, QCAD gives me the same number after measuring it, which means to me that the change I made in the units has not had any effect and I do not understand why. Of course the question
arises on whether the same drawing can have objects drawn with different units types.

So basically I'd like to be sure that when I for example insert a raster image of a real life element I can scale it correctly so that whater I draw on top of it keeps the same scale
and I can do correct measurements and if I happen to change the original scale like from, say, mm to m this will be reflected in the measurements.
So any help appreciated
Thanks in advance

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Husky
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Re: Using the correct drawing units

Post by Husky » Fri Feb 27, 2015 8:51 pm

Hello sinergy,
sinergy wrote:If I change the drawing units to inches, for example, for the same drawing and draw another line having the same "visual" lenght, QCAD gives me the same number after measuring it, which means to me that the change I made in the units has not had any effect and I do not understand why.
QCAD is drawing - like many other CAD Programs - just with Units. To now what the meaning of a unit is in that particular case you have to tell QCAD it is a mm or a inch or what ever unit. So, if you draw with a mm unit - regarding the settings in the Drawing preferences - a Unit called mm will give you the output in mm. E.g. a line which is 5 long means it is 5 mm long. If you change the Drawing Preferences from mm to inch QCAD can't recognize the change and will not automatically convert the drawing from metric to an imperial drawing. Result: Your 5 mm line is now a 5 inch line. To come back on track your next step would be to scale the complete drawing! Select the whole drawing - look for an useful reference-point and scale the drawing - in this case - with a factor of 1/25.4 for x and y. Now your measurement at the 5 Unit Line will give the output of 0.19685 inch and every new entity will be drawn regarding the inch settings.
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sinergy
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Posts: 7
Joined: Thu Feb 26, 2015 12:54 pm

Re: Using the correct drawing units

Post by sinergy » Fri Feb 27, 2015 10:08 pm

Hi Husky
well thanks for your explanation. Do you know if other CAD programs also implement this behaviour? It would seem logical thet they do but, just to make sure
Cheers
Sinergy

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Husky
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Re: Using the correct drawing units

Post by Husky » Sat Feb 28, 2015 8:07 am

Yes, many other CAD programs are working on the same way.
What exactly do you need to do? Just one converting to an other unit or do you need to use different units in the same drawing? QCAD has one feature - and that is something what you can't find in many other CAD Programs - what makes you able to scale a dimensioning.
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sinergy
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Posts: 7
Joined: Thu Feb 26, 2015 12:54 pm

Re: Using the correct drawing units

Post by sinergy » Sat Feb 28, 2015 6:24 pm

Well I'd like to make sure that an image that have imported in the CAD SW is scaled appropriately (whater the unit is) so that I can draw on top keeping the right proportions and that I can print it at the right/desired scale afterwards. Sometime I have found that this last step has not printed the drawing exactly at the scale that I hoped for, but I realized that too late and it has brought me to question whether the drawing was correctly scaled according with the desired unit in the Cad, to start with.
And since I do not have a formal training nor a continuous practice in CAD design I start having doubts like these-
Cheers

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