Let's cover a couple of basics. First, WGS-84 is a DATUM, not a projection. The difference is significant. UTM, on the other hand, is a projection (transverse mercator).
For almost all purposes, the differences between NAD83 and WGS-84 are insignificant at the earth's surface, save for a formal geodesist or someone who was doing a legal survey (and who understood the differences; the surveyors who do are relatively rare...). peter wrote: > Hey all, > > I'm having trouble wrapping my head around the workflow involved in dealing > with multimple projections... > > I'm trying to create a map that I can load into my Garmin GPS, which (I > think) > needs to be WGS84. My data sources are mostly NAD83(CSRS)/UTM, plus I have > some aerial photos that are NAD83/3TM. In general terms, a Garmin GPS does use WGS-84 datums for its positioning. GPS is predicated on a WGS-84 datum, so this makes good sense. The NAD83 datum, however, uses the GRS80 ellipsoid, and the datum parameters are very close to those of the WGS84 datum, and the ellipsoid is the same. > My first step was to reproject the Aerial photos to NAD83(CSRS)/UTM so that I > can create new vector layers of the land features (mostly trails) and save > those as NAD83(CSRS)/UTM shape files. Still having some trouble with this > step... With a little more specificity we might can help? > My next step would be to add those NAD83(CSRS)/UTM shape files to the rest of > the NAD83(CSRS)/UTM shape files and then reproject and save those as WGS84 > shape files. Why don't you see if you can reset the datum in your receiver to NAD83 and use a UTM representation? Otherwise, I'd use NAD83 lat/lon pairs and plug 'em into the GPS. If you must use UTM or 3TM, you need to make sure the receiver will handle them. > Does that sound correct or is there a better way to do it? Thanks much. I suspect you're going about this in a rational manner but I think there are some missing details. gerry -- Gerry Creager -- [EMAIL PROTECTED] Texas Mesonet -- AATLT, Texas A&M University Cell: 979.229.5301 Office: 979.862.3982 FAX: 979.862.3983 Office: 1700 Research Parkway Ste 160, TAMU, College Station, TX 77843 _______________________________________________ Qgis-user mailing list [email protected] http://lists.qgis.org/cgi-bin/mailman/listinfo/qgis-user
