Good Afternoon,
?ÿ
I'm reducing data on a GPS survey from the Middle East and have two points that are 15.317M and 15.403M out of tolerance in my?ÿ baseline processing.?ÿ These two stand alone in their indifference. The only additional information I know of is that the crew I am working with used R8 tribrachs, instead of the R10 rigs they all have and my suspicion is they entered something into the Data Logger and forgot to forward that information to me for confirmation.?ÿ
I have tried adjust all possible configurations in the TBC import menus, and nothing is correcting the error.?ÿ All points were collected in the same time and constellation, so I have isolated these two as "human error" busts.?ÿ Any suggestions would be greatly appreciated, otherwise, I'll be sending them back out to recollect and resubmit.
?ÿ
Best Regards,
?ÿ
?ÿ
Jason
?ÿ
?ÿ
?ÿ
sounds like a geoid height
Look at the antenna height in the Observation Spreadsheet to see if it is obviously wrong?
That was my first search, a simple fat fingered order of magnitude blunder.?ÿ Nope.?ÿ 🙁
?ÿ
I'm leaning that way too, but no other points are included.
I'll have to get the field notes and have a discussion of the start up process.?ÿ This is a static survey across most of Kuwait, and I've been fighting/discussing with the local 'experts' on which datum/geoid/etc to use.....I may not have gotten my message to all involved and can't complain too much for 2 points out of 77 for ground control being recollected.
A height entered as feet instead of meters?
Maybe a couple vectors did not fix, and therefore threw the points out of tolerance. Are you (accidentally) mixing fixed vectors with autonomous positions?
Session Editor yielded no additional reduction, nor have the feet versus meters.
I did catch a glimpse of one of the DCs on the job site, and I saw they had been doing planimetric work with a custom 7 parameter transformation that I instructed them not to use.?ÿ These points were collected by the same crew, so I'm starting to lean on the idea that the data gets recollected, I write up explicit check list type procedures, and see what rolls in after the next collection cycle. I'm glad they are able to help, because it's hot in Kuwait soon, and I really don't want to go back until like, December.......?ÿ ;)?ÿ
Session Editor yielded no additional reduction, nor have the feet versus meters.
I did catch a glimpse of one of the DCs on the job site, and I saw they had been doing planimetric work with a custom 7 parameter transformation that I instructed them not to use.?ÿ These points were collected by the same crew, so I'm starting to lean on the idea that the data gets recollected, I write up explicit check list type procedures, and see what rolls in after the next collection cycle. I'm glad they are able to help, because it's hot in Kuwait soon, and I really don't want to go back until like, December.......?ÿ ;)?ÿ
Yeah, sometimes it's simplest to recollect. But since it's static data, what I sometimes do is revert the whole project to a datum with no projection and definitely no transformation/localization. Taking the transformation/localization/custom projection out of the equation has saved me on several occasions. You could even remove the Geoid and process the data strictly as geometric data.
One could also convert the problem files to RINEX and reprocess if there are suspicious associated Trimble files that might be gumming up the works.
A height entered as feet instead of meters?
If they measured in meters and entered mistakenly as feet, the offset would be smaller than the antenna height.
If they measured in feet and mistakenly as meters, it would take a 22.15 ft antenna height (6.75 m) to give 22.15-6.75 = 15.4 meter error.?ÿ So I don't think that's it unless they had rather unusual setups.
---------
Pedantic note: When working with GPS results, the height should not be referred to as Z axis, as that is the part of the XYZ coordinate system that tells how far you are from the equatorial plane.
Pedantic note: When working with GPS results, the height should not be referred to as Z axis, as that is the part of the XYZ coordinate system that tells how far you are from the equatorial plane.
Good note, and I think not pedantic at all. An awareness of ECEF Cartesian space is really important to understanding map projection distortion along with the basic geodetic idea that mark to mark inverses can be computed without benefit of either a local planar coordinate system or the messier mathematics of geodesics.
Session Editor yielded no additional reduction, nor have the feet versus meters.
I did catch a glimpse of one of the DCs on the job site, and I saw they had been doing planimetric work with a custom 7 parameter transformation that I instructed them not to use.?ÿ These points were collected by the same crew, so I'm starting to lean on the idea that the data gets recollected, I write up explicit check list type procedures, and see what rolls in after the next collection cycle. I'm glad they are able to help, because it's hot in Kuwait soon, and I really don't want to go back until like, December.......?ÿ ;)?ÿ
Yeah, sometimes it's simplest to recollect. But since it's static data, what I sometimes do is revert the whole project to a datum with no projection and definitely no transformation/localization. Taking the transformation/localization/custom projection out of the equation has saved me on several occasions. You could even remove the Geoid and process the data strictly as geometric data.
One could also convert the problem files to RINEX and reprocess if there are suspicious associated Trimble files that might be gumming up the works.
Funny thing...Because the local geoid models are so contested, or Highly constrained, or just plain recommended to not be used, I just collected in WGS84 UTM 38N, Ellipsoid,?ÿ no geoid. This is ground control for a Orthophoto, AT,?ÿ and LiDAR project.?ÿ We plan on tying everything to that, then, at the end, possibly constrain it to the datum they are wanting, with no guarantees, especially since there are PhD Thesis being written on the topic of the datums, subsidence due to resource removal, and massive salt water injection wells for well fields maintenance etc.?ÿ Good Fun.?ÿ ?ÿ?ÿ
I picked a point in Kuwait and got a geoid height of -14.6, this sounds like a geoid height issue.
