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 --------------------------------------------------------------------- List hosting provided by Directions Magazine | www.directionsmag.com | To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] Message number: 5581
