I'm a relatively new surveyor with no formal education on the subject and i've been forced into learning some basics for the company.
I'm confused about the use of the combined scale factor and going from grid to ground and vice versa. I'm using Leica equipment and SurVCE software. I use both RTK and total stations.I was wondering if I could get some help on procedures when surveying on a fresh site with no existing control points. The clients we work for want they survey database (in C3D) to be in grid UTM coordinates but then a local UTM shift is applied using a scale factor (I understand how to do this part in C3D but its the field procedures that have me confused).
In the field upon starting a new job, and making sure the correct projection is being used, I load up a geoid file for the area to be surveyed. I then configure my base and let it read by GPS to give me a starting coordinate. I save this point and it will be used for my tack point for my scale factor. By default the scale factor is set to 1 for my grid to ground conversion (under the Localization->GPS tab in SurvCE). If I leave this as 1 is it technically not in either grid or ground coordinates but somewhere in between? If I let it read a scale factor based on the gps location and that number is >1, does this mean the survey to be performed will be done in ground coordinates? Likewise if it is <1, then it will be in grid coordinates. The SurvCE manual says its best to survey with a scale factor of 1.
For these surveys I also collect static data to be corrected later using the NRCAN-PPP solution.
Any help and some clarification would be much appreciated!
I'd recommend you search the forum for this kind of thing. A lot of ink has already been spilled. It's an excellent and critical question (the answer to which you will understand more deeply over a time period measured in years), but those who would give you the best answers may be weary of repeating themselves.
It will be critical for your career that you understand this subject well.
I'd recommend you search the forum for this kind of thing. A lot of ink has already been spilled. It's an excellent and critical question (the answer to which you will understand more deeply over a time period measured in years), but those who would give you the best answers may be weary of repeating themselves.
It will be critical for your career that you understand this subject well.
start here, these guys wrote the book. there is no short course that is more than a primer science and education/publications ... basic geodesy https://geodesy.noaa.gov/?ÿ
It sounds to me like you are taking UTM grid coordinates, scaling them to ground, and applying a shift. Which is a thing that, while common, kind of makes us purists cringe.?ÿ Better would be to just do everything in the projection system.?ÿ But I understand that this isn't by your choice.?ÿ?ÿ
If so, at that point you simply have local (non-projection grid) coordinates.?ÿ If you want to use your RTK with these local coordinates you will want to do a localization (aka site calibration).?ÿ ?ÿ?ÿ
?ÿOnce you connect go to the Localization then GPS tab, press the icon that looks like a GPS rover next to the scale factor and SurvCE will read the grid to ground factor. The geoid file is for your elevations not your projection. I don't know where you are at,?ÿ but you need to know what projection you want to be on. UTM or maybe state plane
All depends on where you are. There are places where the grid distances are longer than ground distances. Therefore, leaving you with a <1 scale factor to be ground.
You might want to consider using local coordinates in the field and convert your raw data when you bring it into your base drawing.?ÿ Even keeping a separate field drawing if the project is large, will be around for a while or you will doing construction.?ÿ The convention of scaling back and forth all of the time or recording raw data in a projection requires everyone to think what they are doing and all to be on the same page, difficult in some firms but practiced by many.?ÿ?ÿ
I don't know much about Leica or SurVCE software, but hopefully there is some way to check and verify that you are meshing your ground distances to your surface coordinate system. I do know there are some routines in Data Collectors that make you think it's giving ground distances but it's actually inversing along the ellipsoid just like UTM coordinates do. It's important to find a way to check your system numbers against real measured ones.
?ÿ
Here?ÿis a screen shot of an inverse between two located points (#57 to #85)?ÿin a recent job:
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?ÿ
This an LDP projection so the grid azimuths are close to Geodetic, and for these two points the grid distance and ground distance are very close. Because there is almost 300 ft in elevation change it's more luck than anything else that those distances are so close, there is 7PPM to be expected in that large of an elevation shift.
You want to be sure and?ÿverify that the numbers you are?ÿusing actually check to what you are telling everyone you are doing.
And as you can see there is .4' in Geoid height difference in a short distance which really illustrates the need for a Geoid model.
If you are just collecting data I suggest you use your RTK to establish control in the projection/geoid model of your choice then scale & translate later in CAD. If you are using the same controller for RTK and total station then it should be able to use the projection with your TS too.
If you are laying out then you better know what you are doing.
When I am in the field I focus on the data collection keeping it as simple as possible. Warping, bending, and hammering the data is best done in the office to avoid opening a crack in the geoid/ellipsoid interface.
When I am in the field I focus on the data collection keeping it as simple as possible. Warping, bending, and hammering the data is best done in the office.......
I don't know much about Leica or SurVCE software, but hopefully there is some way to check and verify that you are meshing your ground distances to your surface coordinate system. I do know there are some routines in Data Collectors that make you think it's giving ground distances but it's actually inversing along the ellipsoid just like UTM coordinates do. It's important to find a way to check your system numbers against real measured ones.
?ÿ
Here?ÿis a screen shot of an inverse between two located points (#57 to #85)?ÿin a recent job:
?ÿ
?ÿ
This an LDP projection so the grid azimuths are close to Geodetic, and for these two points the grid distance and ground distance are very close. Because there is almost 300 ft in elevation change it's more luck than anything else that those distances are so close, there is 7PPM to be expected in that large of an elevation shift.
You want to be sure and?ÿverify that the numbers you are?ÿusing actually check to what you are telling everyone you are doing.
And as you can see there is .4' in Geoid height difference in a short distance which really illustrates the need for a Geoid model.
Ok so by reading this grid to ground scale factor from the rover head, it puts my coordinates into ground. If i'm post processing for a PPP solution or I guess the american equivalent, this step is not necessary. I just need to remember that I need to process the survey to ground once i'm back at the office. Then I can import the processed file into my civil database to have grid utm coords and local utm coords for the client.
Thanks for all the responses guys, I definitely need to do more research on the subject and get my head wrapped around it more before being completely comfortable!
