Most of my work is in Alaska State Plane Zone 4. I'm working on a sixty mile long design survey and I've just found myself crossing over into Zone 3. I feel compelled to stay in Zone 4 for obvious reasons. The vast majority of my work on this project is in zone 4. The three mile segment I'm currently working on is bisected by the 148 degree meridian, the divide between zones 3 & 4. The mapping angle is approaching 2 degrees. So here is my dilemma, how far do I push it. I'm under no constraints and have the freedom to do as I see best fit, for better or worse.
I'm just curious how others deal with this type of issue. I know enough to know that I don't know enough to make an educated decision, yet. I do know that I am grateful that I will not be required to file a ROS for this project in California. 😉
~Willy
Just because I'm paranoid, doesn't mean they aren't out to get me.
Personally I would stick with one zone. Either the Engineer will understand how to deal with the distortions or they will ask for the data on a projection that approximates ground. Either should be simple but avoid 'splitting' the project if at all possible...
I'm not familiar with how the zones are set up in AK, but you should have very little, if any problem, extending one zone into the next. You've identified one issue of mapping angle. And depending on which way you are extending versus the way the zones run you may have scale factors exceed 1:10,000. But if you pay attention to the details you should be fine.
And I agree with the comment of keeping it all in one system.
I agree that it would be best to keep it in one system and just extend it out, keeping track of the distortion so I can relate it to ground locally.
These two particular state plane systems are universal transverse mercators.
I suppose when the mapping angle approaches 90 degrees, I've probably gone too far. 😀
Just because I'm paranoid, doesn't mean they aren't out to get me.
> I agree that it would be best to keep it in one system and just extend it out, keeping track of the distortion so I can relate it to ground locally.
>
> These two particular state plane systems are universal transverse mercators.
>
> I suppose when the mapping angle approaches 90 degrees, I've probably gone too far. 😀
Clarification:
The Alaska State Plane Zones in question are "Transverse Mercator," but the term "universal transverse mercators," would imply one or more or the UTM (Universal Transverse Mercator) Zones covering Alaska. That could be Zones 3, 4, 5, 6, 7, 8, and maybe Zone 9 in Mainland Alaska alone.
Be careful so that some dummy (like me) doesn't use the WRONG projection parameters (SPC v. UTM).
Loyal
I've been starting to hear more about these Snake Grid projections:
http://www.snakegrid.org/about_snakegrid_technical_explanation.php
These are supported in TBC 3.21; I haven't tried messing with one yet.
>
> The Alaska State Plane Zones in question are "Transverse Mercator," but the term "universal transverse mercators," would imply one or more or the UTM (Universal Transverse Mercator) Zones covering Alaska. That could be Zones 3, 4, 5, 6, 7, 8, and maybe Zone 9 in Mainland Alaska alone.
>
> Be careful so that some dummy (like me) doesn't use the WRONG projection parameters (SPC v. UTM).
>
> Loyal
Thanks Loyal. Nothing will mess a guy up faster than mixing units.
I type faster than I think at times and do my best editing after hitting send.
I also sometimes miss the days when my world was flat. Life was simpler back then. A little distorted at times, but simpler.
TGIF.
Just because I'm paranoid, doesn't mean they aren't out to get me.
Okay,
At first glance these are just low distortion projection utilizing some flavor of oblique projections. Not hard to do but I find it interesting that they are able to sell them.
As for the problem of working in two zone, usually the is some overlap in the coverage. In most state the zones are arbitrarily defined to match county lines. Just look at the grid scale factors to see if they meet your requirements. I would say the mapping angle is a red herring, even it really just represents the distance you are from the central latitude of the projection. In a Lambert system the mapping angle could be 45 and the grid scale 1.000.
As for the comment about the engineer, I would say it is our job to understand the distortions and relay consequences to them.
The comment about the Engineer relates to Engineers who understand State Plane Coordinates and how to design using them. If they know what they are getting and how to use it there is no need for me to fiddle with a custom projection or coordinate transformation. If they don't then yes, I should walk them through what will get them working.