?ÿ ?ÿDear sirs
I need to recommending me about observation time for static observation in Renix data inorder to post processing with OPUS, for static observation is carried out for establishing a number of control points (i.e Bench Marks) for large area residential builing construction. We have a CORS station, the distance between CORS station and proposed residential area are 550 km. i have receiver Multiple frequencies
I would not recommend using OPUS Ortho Heights for Site Benchmarks; although it has become the 'go to' method for many. Your data might not match other forms of data and you might not meet any required specifications, otherwise, I would go with three 23 hours sessions. Many will say 4 hours of observation will give you a 1cm vertical, but their product seems to indicates differently. 550 kilometer is a long way.?ÿ
Yikes establishing vertical control using GPS constrained by OPUS position(s) 550km away for a residential subdivision is insane.?ÿ Concerning drainage, earthwork and sewer grades they have to conform to adjacent local Benchmarks no matter how badly they match with "GPS" elevations.?ÿ I'd suggest a GPS scenario constrained on high order nearby stations tied to the local cadastre for horizontal location is acceptable and do simple levelling from nearby benchmarks to establish construction benchmarks from which you can run construction work using Total Station/levelling gear onsite to get within a few hundredths everywhere onsite.?ÿ But that's just me, possibly being anal and therefore no longer competitive.
OTOH recently I've witnessed subdivision construction done completely by GPS with no issues except the flatwork guys complaining their stringlines jump up and down because of really loose vertical control.?ÿ It could be builders/inspectors don't care anymore and lousy is good enough.?ÿ Sad.
550 km is a long way. So far that I have to assume that you are not in the continental United States.?ÿ
The word "Benchmark" leads some of us to assume that you are trying to establish marks for high quality geodetic elevation. Is that so? Elevation has always been the weakest dimension to establish using GPS.?ÿ
For ordinary control points, with or without elevations, I do not recommend establishing them by a series of independent OPUS sessions - whatever the occupation time or number of repetitions. Much better to establish a single starting point using OPUS and then densify your network of control monuments using ties by local GPS vectors or traversing, and adjust the whole batch using a least squares software.
The error in a GPS vector might be something like 0.5 cm+0.1 ppm. In a 550 km long vector that adds up to something on the order of +/-6 cm in that vector. Not really a big deal in a measurement between 2 points 550 km apart, right?. But if you establish 2 such points 100m apart using 500km long vectors you might find, when you set up on one and measure to the other, the distance between them not agreeing by up to 12cm! That would not be acceptable.?ÿ
Anyway..... as far as using OPUS for that one point to start from .... at least a couple of 4 hour or longer sessions (2 hours will get you a result, longer is better). One in the morning, one in the afternoon.?ÿ
On the other hand, if you really are trying to establish a network of elevation reference benchmarks using this method a good many more repetitions are in order. Differential levelling will probably be quicker, and certainly more precise if done well.?ÿ?ÿ
?ÿnot in the continental United States.?ÿ
The coordinates posted his other thread are in eastern Iraq.
And the pk-pk vertical for a 4-hour session was 16 cm.
I'm not fully conversant with the math involved, but an OPUS position being the product of 3 vectors, all with an error of some magnitude, I assume will have a total error greater than the sum of its parts.?ÿ
Vectors are computed from each of the three selected stations to find three position estimates (reported in the details of the extended report if you ask for it). The reported position is the mean of the three solutions. The pk-pk in each axis is the max minus min of the three.
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Thank you from the heart
One thing to note, OPUS only uses GPS (unless that has recently changed) so the other online processors.?ÿ Alternatively, given the distance to the nearest CORS you may want to try a SPP solution.
Like Mark pointed out, bring the control into a single point to hold as control.?ÿ Then spread out locally from there.?ÿ That should help keep the local control relative.
Try submitting the data to Trimble centerpoint RTX. It will return a ITRF14 coordinate, which can be used with EGM08 to get a "sort-of" elevation which probably won't match any existing control in the area.?ÿ
One method if you have only one receiver would be to do an occupation at your site and then another one on a benchmark in the area (preferably more than one) and submit to RTX post processing. By differencing you can get a reasonably accurate elevation on your site.?ÿ?ÿ
@john-hamilton Agreed. If this users in not in the USA, OPUS is not recommended. Trimble CenterPoint RTX post processing (free service) uses Trimble owned CORS around the world, and will use Galileo, Glonass, and Beidou satellites unlike OPUS that uses only US/GPS satellites.
I agree that Trimble's service will likely yield better results. Although OPUS tends to be used by the majority of users in the USA, we are using Trimble RTX-PP more and more. The additional constellations help a great deal in less-than-perfect satellite conditions and tend to obtain more repeatable vertical values.
Not to mention it accepts RINEX files, not just proprietary Trimble files...
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