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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