In 2022 the National Geodetic Survey (NGS) will be coming out with a new horizontal and vertical datum. This will mean a change in both horizontal and vertical coordinate values. Implementation of the new datum will require legislation to redefine our state-based coordinate system. This is an effort ODOT is willing to work with the OSLS, the State Board and the GIS community to accomplish.
NGS is going to allow states to have input on their state plane systems. The new state plane system can be two tiered. We can keep our current two zones, North and South. Those projections can be modified to where instead of using the Ellipsoid for the plane “elevation” a “topo” elevation can be used. This will help reduce the grid to ground error. This what NGS will probably do for Oklahoma, if we do not make any changes to our coordinate system. NGS has requested input from each state as to what they want their coordinate system to look like. NGS has to have the preliminary design submitted to them by December, 2019 and the final design submitted to them by December, 2020.
It is with that thought in mind that ODOT Survey Division proposes a two tier system. The first plane will be one plane for the whole state (for the GIS community). This would do away with the old north zone and south zone that we currently have and make one plane for the whole state. The second plane will be Low Distortion Projections or LDP (for the surveying community). This would break the state up into different zones, with each zone having the grid to ground differences less than 1:50,000. We will not address all the specs for LDPs in this memo, but a google search of low distortion projections will provide a number of good papers written on this subject. The drawback to this two tier system, is it require multiple zones. We at ODOT think the benefits outweigh the nuisance of multiple zones.
ODOT Survey Division will be talking to other states, that have LDPs and seeking guidance from NGS on the subject. We are also going to see who could compute the zones for us to make them compliant with NGS. This is a subject that ODOT Survey Division feels that we should take the lead in and submit our findings to the OSLS, the State Board and the GIS community for their input. This is the exact way the Kansas Department of Transportation implemented their LDPs. Survey Division will not implement the LDP’s in Oklahoma until NGS implement’s their 2022 datum.
I am sure there will be more on this subject in the future. Any comments about the use of LDP’s and/or the use of one or multiple zones for the whole state can be sent to: OKLDP@odot.org
Kyle King. Chief of Surveys
Geoffrey King, Assistant Chief of Surveys
Steve Telford, Survey Division Support Branch Manager