Dloc,

I am no expert on LIDAR but will offer these questions and observations.  The more "flat" the topography the better spec you will want.  IE if the LIDAR is +-8" and the local field has undulations of less than that will it be expressed vs say with +-1"?

Having said that I have messed with regular DGPS elevation data collected with a combine and surfaced it out compared to DGPS elevation data taken with a Veris.  Obviously the Veris was collected rapidly (less time to "drift") vs the combine collected at a much slower pace.  The rapidly collected data seemed to discribe the topography much better than the slowly collected data.  Obviously both not as well as with RTK.  So.....my question is on a particular local field in the LIDAR project would the same hold true and thus it would be pretty good or is the +-8" absolute.  A long time ago when I talked to some LIDAR company on the front range it seems they told me the accuracy is very good between one point and an adjacent point but one point compared to another point on the other side of the field was less accurate.

Finally I have used lasers for a long time to collect elevation data prior to using RTK equipment to do the same.  I found I could collect and design with RTK just fine and am starting to use RTK for machine control as well.  The first time I collected with RTK and designed a surface for laser control I crossed checked high (cut) points against low (fill) points and found the relative laser difference between them to be quite good thus building my confidence in RTK elevation data.  I was worried about the RTK +- vertical error spec being not as good as the published +- error of laser.  That was assuming with a laser one stayed within the 1000 foot limit of the transmitter to minimize error from the curvature of the earth.

Which then in GPS goes to stuff I need to learn more about like elipsoid, geoid, and orthometric heights.  Depending on who you talk to, their perspective, and education on this whole thing you will get different answers ranging from street and field smart answers to well educated book smart answers.  In a given farm field I know that I have had great success using RTK data for the whole field and analyzing it against yield as well as designing surface solutions to fix those problems.  HOW that relates and ties into larger macro data sets (like LIDAR) most likely is a whole different issue.

Arnie