Thanks to Neil for solving my problem, by specifying the new projection as I
imported a dxf version it worked very well.
I also noticed the resulting map seems to have a better "fit" with the rest of
my data when I assigned the new projection which had the calculated affine
parameters, compared to using the set transformation option in the in dxf
import. I'm not sure why that is, maybe the set transformation option doesn't
take into account scaling factors? I don't know, just a guess! Does anyone know
why the results would be different using those two methods with the same control
points?
Dan
"Neil Moseley" <[EMAIL PROTECTED]> on 11/15/2001 07:43:08 PM
Please respond to "Neil Moseley" <[EMAIL PROTECTED]>
To: Dan Page/HullOttawa/PCH/CA@PCH,
[EMAIL PROTECTED]
cc:
Subject: Re: MI-L Affine Transformations
Dan,
Your projection clause looks OK, but it does not work to simply change the
projection of the map for a table that is already created as non-earth.
If you were to import the DXF and specifiy your newly created projection in
the import DXF dialog it should work.
Alternatively, export to a MIF file, open the .MIF in a text editor and
replace the Non-Earth projection clause with your newly created affine
projection, then import.
If this is a one-off, then the way you did it is probably the simplest.
However, if your local coordinates are used regularly then it is worth
setting up the local projection. This has the added benefit of being able
to display the map in the local coordinate system if required.
Regards
Neil Moseley
----- Original Message -----
From: <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Friday, November 16, 2001 5:40 AM
Subject: MI-L Affine Transformations
> Regarding my earlier post (at the bottom of this e-mail) about
transforming a
> non earth map to a real earth coordinate system. I ended up converting
the file
> to dxf and importing it into MapInfo and setting up a coordinate
transformation
> using the two control points that I had. But I'm not sure how accurate
this is?
> Does anyone know what the differences are between using this method and
using
> the affine transformation method or using other softwares that do this
kind map
> transformation from a non earth to a real earth coordinate system? Are
some
> transformation methods more accurate then others?
>
> Information about software that can do this kind of transformation was
also
> suggested such as the Traverse PC and Discover program, are there any
other
> software packages that can do this? In what situation should one use these
> programs or use the affine transformation method rather then just setting
up a
> coordinate transformation while importing a dxf version in MapInfo? Any
insight
> would be appreciated.
>
> TIA
>
> Dan
>
> ---------------------- Forwarded by Dan Page/HullOttawa/PCH/CA on
11/15/2001
> 04:24 PM ---------------------------
>
>
> Dan Page
> 11/15/2001 01:25 PM
>
> To: [EMAIL PROTECTED]
> cc:
> Subject: Affine Transformations
>
> I have an AutoCad drawing of a survey that was done in non-earth
coordinates
> "metres" and would like to overlay some GPS data which is in UTM83 Z18
> coordinate system. I was reading in the MapInfo manual and also the MI
mailing
> list archives about affine transformations and thought I would give it a
try but
> doesn't seem to be working and was wondering if anyone might know what I'm
doing
> wrong.
>
> These are the two control points that I'm using.
>
> GPS UTM83 Z18 AutoCad (local coords. metres)
> 1.
> X: 374408.5 3031.93
> Y: 4986086.05 3033.78
>
> 2.
> X: 374701.6 3325.37
> Y: 4986089.2 3054.71
>
>
> Using Neil Moseley's Affine Calculator at
> http://members.iinet.net.au/~mose/prod03.html, which was very useful,
> the affine parameters were calculated and gave me the following results.
>
> A= 1.001811748958
> B= -0.060642418938
> C= -69686.58510395
> D= 0.060642418938
> E= 1.001811748958
> F= -5014790.84331770
>
> "My Grid Name", 300x Base Projection Clause,
1.001811748958, -0.060642418938,
> -69686.58510395, 0.060642418938, 1.001811748958, -5014790.84331770, Bounds
> Clause
>
> Using those parameters I created the following coordinate system at added
this
> line to the "Universal Transverse Mercator (NAD 83)" section of the
mapinfo.prj
> file
> "Affine transform to UTM83", 3008, 74, 7, -75, 0, 0.9996, 500000, 0, 7,
> 1.001811748958, -0.060642418938, -69686.58510395, 0.060642418938,
> 1.001811748958, -5014790.84331770, 0, 0, 10000000, 10000000
>
> I then start up MapInfo and open the local survey table (non-earth) then
through
> Map>Options change the projection to the new Affine transform projection I
> created.
> Then everthing just disappears and when I try to "view entire layer" still
> nothing shows up on the screen. Can anyone tell me what I'm doing wrong?
>
> TIA
>
> Dan
>
>
>
>
>
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