Thre's no apology necessary, there was no irritation here. I just have to
try to make sure nothing is missed when explaining sometimes complex
projection issues in MapInfo Pro so as not to confuse anyone reading the
explanation any further. This projection type has already been sent as as
a feature request to MapInfo Pro Development.
Regards,
-Bill
"Robert Karr"
<RKarr@legislatu To:
<[EMAIL PROTECTED]>, <[EMAIL PROTECTED]>
re.mi.gov> cc: <[EMAIL PROTECTED]>
Subject: Sum: MapInfo - MichGeoRef
02/19/2003 02:03
PM
Greetings All:
A copy of this is being sent to Bill Wemple at MapInfo. He was kind
enough to respond directly, and I think I irritated him with some of my
email. I apologize for that. And, I hope he will correct anything I
paraphrase that is wrong.
Basically, Mr. Wemple explained that MapInfo implemented a different
version of Oblique Mercator than used in MichGeoRef. USGS requested
MapInfo build a Hotine Oblique Mercator projection for Alaska, quite
some time ago. The version used in MichGeoRef is the Standard form.
The important difference is the Hotine defines false grid coordinates
at the natural origin, and the Standard uses the projection center. He
also indicated there should be no more than a few meters difference, and
anything more was due to incorrect parameters. I have not researched
this enough to explain the precise definitions of "natural origin" and
"projection center".
He suggested, while waiting for MapInfo to implement the Standard
Oblique Mercator, we reproject SHP layers that are in MichGeoRef to
Michigan State Plane, using ArcView, before importing them into MapInfo.
Sooooo.....For Michigan users of MapInfo who have already translated
many SHP layers originally mapped in MichGeoRef, the effect seems
minimal or non-existent. On a technical level, I don't know if there
will be any effective difference between layers translated using Hotine
or Standard (when implemented). I suspect not.
EXCEPT for those of us needing to map now in the Western part of the
state, and who do NOT have access to ArcView. This leaves me with asking
the originator of the file (or someone else who has ArcView, off site
and outside our organization) to translate the files for me.
Or....Using a messy work-around.
I've found by using the UT to make a MIF, take the MIF into a
wordprocessor, replace the projection info with MichGeoRef's specific
parameters (with appropriate bounds), then import it into MapInfo, it
works. By "works", I mean the western part of the state falls into place
as well as the data in the rest of the state. You also end up with
bounds that closely surround the whole state, not cutting through it.
I still do not understand how, using the Hotine implementation, we can
get data in most of the state to plot so close to where it should be and
yet have MapInfo apply default bounds that are so far off that it cuts
through the state, "smushing" the data in the western part of the state
at the bounds limit.
The irritation I've caused Mr. Wemple is rooted in my inability to
explain this effect. I apologize again for this lack (and my wordiness),
but I still believe Mr. Wemple has missed this point.
If the default bounds that MapInfo applies in this case had been
roughly 500 miles wider, we would never have had this discussion.
Mr. Wemple, thank you very much for participating and providing
information.
One last question:
Do we need to make a formal request to MapInfo to add a Standard
Oblique Mercator projection, and if so, to whom should we direct it??
....thanks again ....Bob
Robert Karr Phone: 517-373-3028
GIS Operator FAX: 517-373-0171
Science and Technology Division
Legislative Service Bureau
Michigan State Legislature
124 West Allegan Street, 4th Floor
pob 30036
Lansing, MI 48909-7536
USA
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