I have a drawing with the units sets in feet and inches. Its a localisation drawing.I took the coordinate of three points in this drawing, convert them in metrics, put them in my total station, went to the field and tried to locate one of them with the coordinate of the other two. It didn't work.Someone scale the drawings into metrics and then gave me the coordinate of the points, wich were not the same as the converts one. I went back to the field and easily find my third point.Someone could explain it???????????  

Sounds like the drawing had to be scaled first.  So what's the problem?

May be, i'm not clear enough.In the drawing, the coordinate of my point is for example: 5',5'If I convert it in meter it is now 1.52,1.52But if I scaled it to meter I will obtain something different.Why 

Hello, are you making that "scale convertions" by hand or informaticly ?
If you do it by hand you will have to be very precise ( use the software "convert.exe" for example or the windows calculator with ctrl+c / ctrl+v ).
The better way is to do it informatictly by using the different parameters on Autocad.
You can work on a same file seting the units on inch , foot , mile millimeters etc... with different units.
You can work in meters and put dimensions in an other unit by setting the "DDIM" parameters.
You can insert a file in millimeters in a file in inches without having to "rescale" it provide that you have the "DDUNITS" OK on each file. 
I am personnaly using X,Y,Z location and it's OK provide you use the good 0,0,0 and units etc...
A good file informaticly drawn with an absolute precision will give you exact information in feed back.
Hope this will help.

Hello N� 2 :
Precisions in mesures convertions :
1 inch = 25.4 mm
1 foot = 12 inches = 304.8 mm so that :
5 feet = 5 x 304.8 = 1524 mm = 1.524 m and not 1.52 m
1 yard = 3 feet = 914.4 mm
1 furlong = 220 yards = 201'168 mm
1 mile = 8 furlongs = 1'609'344 mm
 
Precisions in dimensions on Autocad settings :
In "DDIM" comand ( dimension settings ) pay attention to :
Principal units :
Precision : 0.000'000'00 ( 8 digits availables after the point )
Approximation ( approximate translation from french ) : 0.000'000'000 ( infinite digits availables after the point )

Whenever you want to work on coordinates, your drawing should have to be on metric units and not architectural. There is a scale factor of 12. For example, if your drawing is in feet and inches and you want to convert it to metric, you have to scale down your drawing using scale factor 1/12.
Similarly, if your drawing is in metric units and you want to change it to feet inches, you have to scale up your drawing using scale factor 12. Now when you reduce the scale, it definitely changes the location of all points except base point. So the point 5',5' in your drawing is no more on that coordinate and shifted to some other location. That is why you are getting different values after scaling your drawing.
Hope it answers your question.

Are you sure of those scale factors?  They don't look right to me.These common conversion factors should be used when converting from imperial to metric and vice-versa.
1 inch is 25.4 mm
1 mm is 0.0393700787 inches

John Connor2011-08-19 14:30:47

1/12th of a foot is 0.0833 inches which is not a metric dimension.  Surveyors in the U.S. commonly use decimal feet/inches when taping distances and showing them on a property map.  Example: 125.67' (that would be 125 feet 8 inches).

I'm quit shocked to read that the scale factor between meters and foot/inches is 12.
In fact 12 is the scale factor between inches and foot and nothing else ( 1 foot = 12 inches )

Hey don't get shocked. Your conversion above is absolutely correct. I didn't mean to say that. May be whatever I had written was wrong but I remember I have worked out like that but only to put architectural building built in feet dimension on topographic survey plan.

FarooqiSA: Then your conversion was between different types of imperial units which would be correct.  However, the person who started this thread is going between two DIFFERENT types of units: imperial and metric so you're conversion would be incorrect.

Hello FarooqiSA, I apologise for the "quit shocked" even if I'd put a little bit of humour inside ( quit instead of quite ).
I have uploaded a new DWG file ( FEET-METERS.dwg ) showing different kind of settings of file + setting of dimensions.
See the drawing with dimensions in feet + alternative dimensions in meters + coordonates in absolut position towards the 0,0.
See inside the white circle dimensions in architectural + alternative dimensions in meters.

John Connor: I realized that only after getting feedback from you and the other guy. And I apologise for being putting irrelavant post here. But at least I learned something from that. Thanks

philippe Joseph: Thanks for your upload but can you please tell me from where I can download that drawing. Sorry to bother you, I am new to the forum and don't exactly know how to do it.

philippe Joseph: I have done with the download. It was in CAD blocks. Thanks a lot.

No problems FarooqiSA, I supose that we all come to that site to learn ( me first ) and if we can help each other it's sust a "plus" that will please us.