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Zone Transformation oddity

15 REPLIES 15
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Message 1 of 16
Loridi
392 Views, 15 Replies

Zone Transformation oddity

Due to my field of work I have to sometimes perform zone transformations. Since I use Map there is a way, however as of late it has done something rather odd. First I'll show how I've been doing the transformation, please let me know what's going on.

First I open the drawing, set the units to metric and then set the datum, for this example I'll use NAD83, Zone 14 and metric.
Second I export the drawing into a shape file.
Third I open up a new drawing setting the units to metric then set the global coordinates to Lat/Long.
Fourth I export that into yet another shape file.
Fifth I open a new drawing and set the units to metric and the datum to NAD83, Zone 15.

What comes up is a similar shape, however it's roughly now 80% of it's original size.

What's going on?
15 REPLIES 15
Message 2 of 16
rick-chappell
in reply to: Loridi

What is the data and where is it going? I don't see any relationships with the three drawings and the exports. Edited by: rick-chappell on Feb 16, 2010 8:41 AM
Message 3 of 16
Anonymous
in reply to: Loridi

? set the units to metric ? Where are you setting this at? In the Drawing
Units dialog under the the Insertion scale? That is only for blocks, images,
or xrefs inserted or attached to a drawing.

What are you doing between steps 3 and 4? Looks like you created an new dwg
then exported it, are there objects in the dwg and where did they come from?

Are you exporting to shp format creating new dwg and importing the shp file
back in to convert/transform the objects?

The dwg attach and query method works faster and easier to transform/convert
between coordinate systems.
--

Murph
http://map3d.wordpress.com/
Message 4 of 16
Loridi
in reply to: Loridi

It's basic line work
Message 5 of 16
Loridi
in reply to: Loridi

Third I open up a new drawing setting the units to metric then set the global coordinates to Lat/Long.
Fourth I export that into yet another shape file.
____

I guess I should explain in greater detail. If I don't make certain the units (type "units" at the command line) are metric it can give me odd transformations.

The DWG's I deal with are fairly basic in that it's just linework and some dimensioning, but I'm concerned with the linework only. In some cases I'm asked by a coworker to transform a NAD83 Zone 14 drawing to a Zone 15 when the drawings straddle the lines. I had asked the people of AutoCAD how to do so and that was what I was told to do.

I am exporting to shp format, creating new dwg and importing the shp file back in to convert/transform the objects?

I could not find what you were referring to. If there is another way please let me know.
Message 6 of 16
Anonymous
in reply to: Loridi

http://www.thecadgeek.com/blog/2008/01/11/converting-a-drawings-coordinate-system/

--

Murph
http://map3d.wordpress.com/


"Loridi" wrote in message news:6337246@discussion.autodesk.com...
Third I open up a new drawing setting the units to metric then set the
global coordinates to Lat/Long.
Fourth I export that into yet another shape file.
____

I guess I should explain in greater detail. If I don't make certain the
units (type "units" at the command line) are metric it can give me odd
transformations.

The DWG's I deal with are fairly basic in that it's just linework and some
dimensioning, but I'm concerned with the linework only. In some cases I'm
asked by a coworker to transform a NAD83 Zone 14 drawing to a Zone 15 when
the drawings straddle the lines. I had asked the people of AutoCAD how to
do so and that was what I was told to do.

I am exporting to shp format, creating new dwg and importing the shp file
back in to convert/transform the objects?

I could not find what you were referring to. If there is another way please
let me know.
Message 7 of 16
parkr4st
in reply to: Loridi

loridi

back to the first drawing. if you open it and then enter adesetcrdsys command what is the coord. sytem of the drawing or is the current map entry box for the coord system blank?

Dave
Message 8 of 16
Loridi
in reply to: Loridi

blank, our contractors use a wide range of AutoCAD compatible programs
Message 9 of 16
rick-chappell
in reply to: Loridi

A) I follow the first two steps - you end up with a NAD83, Zone 14 and metric shape file converted from a drawing.
B) I follow steps 3 and 4 - you end up with a Lat/Long shape file converted from a drawing.
C) I follow step 5 - you end up with a drawing set to NAD83, Zone 15 and metric.

I don't follow "What comes up is a similar shape, however it's roughly now 80% of it's original size."

Is this after an export done after C (similar to A and B)? Shape similar to what? What is 80% of its original size?

How do A, B and C relate to each other? Ie. is it the same drawing you are converting 3 times (resulting in 3 different shape files)?
Message 10 of 16
Anonymous
in reply to: Loridi

Rick,
What I get from the OP is they are assigning the NAD 84 zone 14 Meter CS to
a dwg, exporting the line objects to SHP, then open a new dwg and set the CS
to a Lat/Lon and import the shp they just exported, then turn around and
export that to another shp. Then in another new dwg set the CS to NAD 84
zone 15 Meter and import the last shp file.

--

Murph
http://map3d.wordpress.com/


"rick-chappell" wrote in message news:6337267@discussion.autodesk.com...
A) I follow the first two steps - you end up with a NAD83, Zone 14 and
metric shape file converted from a drawing.
B) I follow steps 3 and 4 - you end up with a Lat/Long shape file converted
from a drawing.
C) I follow step 5 - you end up with a drawing set to NAD83, Zone 15 and
metric.

I don't follow "What comes up is a similar shape, however it's roughly now
80% of it's original size."

Is this after an export done after C (similar to A and B)? Shape similar to
what? What is 80% of its original size?

How do A, B and C relate to each other? Ie. is it the same drawing you are
converting 3 times (resulting in 3 different shape files)?
Message 11 of 16
Loridi
in reply to: Loridi

I've just tried it again with a 1x1 km square, around the coordinates of 300 000, 6 000 000 (X,Y or easting, northing):

I set the units to metric, set the datum to NAD83 zone 14;
exported it into a shape file (lines);
opened a second drawing and set the units to metric, the datum to Lat./Long.;
exported it into a second shape file (lines);
opened a third drawing, set the units to metric, the datum to NAD83 zone 15;
imported the second created shape file into this drawing;

Now I have a 1003.8 metre by 1003.8 metre box at obviously different coordinates. The coordinate shift is understandable, but what's going on with the dimensions?

From what I gather from my original results, I placed incorrectly it at 6 000 000, 300 000. But this still doesn't explain the alteration of the size of the transformed box with the correct coordinates in the original placing.

wtheck?
Message 12 of 16
rick-chappell
in reply to: Loridi

That's what it sounds like, but it is a convoluted enough process I wanted to be sure the OP is thinking it through completely.

I think I understand why someone would suggest a conversion from NAD 27 to go through a LAT LONG - there are some areas where the NAD27 to NAD83 won't work mathematically, so some folks suggest the Lat Long as a median (you will gain a 200 m increase in the Y).

Of course, the conversioni to shape each time is a little excessive. I would suggest doing a simple Map conversion with attached DWGs (the method Murph linked) from the initial to the target, and then do it back to compare the results. If that is getting you problems, I might start looking at other options.
Message 13 of 16
rick-chappell
in reply to: Loridi

Keep in mind, you are going from a flat to a round system and then back. Each process has some error involved. The amount of error becomes more significant as you go further North and as you get toward the "boundary" of the UTM zone (further away from the central meridian). I don't knkow what the amounts of error your location, so I don't know what's appropriate. I bring it up to remind you this is not an exact science.
Each transformation introduces additional error. Not to mention some minor issues in converting data formats (DWG to shape, etc). Edited by: rick-chappell on Feb 16, 2010 11:02 AM
Message 14 of 16
Loridi
in reply to: Loridi

Thanks, and thanks to everyone who posted to help me with my Transformation problem!
Message 15 of 16
parkr4st
in reply to: Loridi

if the original drawing does not have a CS assigned, then the objects in the drawing are not on a CS. Wouldn't objects drawn without the assignment of a CS not be aligned to the CS? Therefore when you assign the CS and the transform then to another CS the objects should do weird things like lose shape and area during tranformation. i.e a rectangle drawn without the assingment of a CS has four 90 degree corners, a rectangle drawn with a CS assigned would taper a mite toward one earthly pole or the other being on a round earth surface?

If you have the drawing drawn with a CS, save it, open a new dwg, assign the destination CS, then attach dwg 1 and query it into the second dwg using all for the location transforming it during the import. Believe that would give your desired results.

Dave
Message 16 of 16
AllenJessup
in reply to: Loridi

I might not quite understand what you're looking for as a final product. But it seems to me that you're starting with 2 drawings and ending with one composite drawing. What necessitates the intermediate step of exporting to shape files? Can you query the 2 original from a new drawing? If the coordinate systems are set correctly in each drawing you might get better results.
Allen


Allen Jessup
Engineering Specialist / CAD Manager

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