Grasshopper curiosity question #31415:
Take any given geodetic point...say N43 x W73, and calculate the convergence for two overlapping grids. In this case, the UTM zone would be 18, with a central meridian of 75 degrees, and for SPC zone 4400, the central meridian is 72-30-00 degrees.
The convergence for the former is 01-21-51.47. The convergence for the latter is -00-20-27.61, a difference of 01-42-19.08.
So is it true that the relative angle between two overlapping grids will always be the same, no matter where within the same two grid zones you are? I tried playing with the converters for each, but couldn't come up with anything conclusive.
No, they shouldn't be the same, but test it out, put points on each meridian and see what you get.
No. Not sure how you came to that conclusion.
The convergence angle is different at every position.
This is easily seen on OPUS results.
leegreen, post: 364414, member: 2332 wrote: No. Not sure how you came to that conclusion.
The convergence angle is different at every position.
Only because I assumed a grid was a rectilinear arrangement of parallel lines, and that two such grids, each oriented to a different meridian, would, relative to one another, always form the same angle. I'll have to read more on how these zones (for both UTM and SPC) are created.
rfc
Download this USGS Professional Paper (1395):
https://pubs.er.usgs.gov/publication/pp1395
It will tell you pretty much everything your ever wanted to know about Map Projections (and a lot more).
Loyal
rfc, post: 364424, member: 8882 wrote: Only because I assumed a grid was a rectilinear arrangement of parallel lines, and that two such grids, each oriented to a different meridian, would, relative to one another, always form the same angle. I'll have to read more on how these zones (for both UTM and SPC) are created.
Hmmm, maybe if both were the same projection and had the same parameters except for the central meridian? I don't think the difference would be the same, but there should be a definite pattern between the two.
Loyal, post: 364472, member: 228 wrote: rfc
Download this USGS Professional Paper (1395):
https://pubs.er.usgs.gov/publication/pp1395
It will tell you pretty much everything your ever wanted to know about Map Projections (and a lot more).
Loyal
Oh my word. That will keep me busy for a while. Thank you:-)
