I am a bit of a novice when it comes to LDP's and I have setup a new LDP to access the practicality on some of my jobs. I am using TBC and the setup seems fine. The question I have is do I assign a geoid model in my projection or not. The results I am seeing in the field, the elevations seem to be poor. This could be the result of me assigning a geoid model when I shouldn't or it could just be slop in the network RTK I am using. The elevations in the network are typically not the best. I am going to run some static and check those, but in the meantime, I thought I would ask here.
I also am using Carlson Standalone for most drafting and am wondering if anyone has suggestions on to handle LDP's in that software...thanks in advance.
You should be able to use a geoid model with an ldp just like you would with SPC with no adverse effect.
When properly setup, your data-collector SHOULD access the GEOID Model (say GEOID12a) exactly the same way that it would if you were using a State Plane or UTM projections.
The Base-Station [ECEF] XYZ is combined with the Base-Station HI, the dX, dY, dZ vector (L1-PC to L1-PC) is applied, then the Rover HI is applied. This returns the Rover [ECEF] X/Y/Z at the “point” (GRP), which the Data-Collector then transforms to a Latitude, Longitude, and Ellipsoid Height.
At this point in the process, the Data-Collector SHOULD solve the GEOID 'N' value for that “point,” and apply it to the Rover GRP Ellipsoid Height, returning a NAVD88 Height (assuming that you are in the US that is).
Of course the “accuracy” of the returned NAVD88 height is dependent on the “accuracy” of the Base GRP coordinate (and height) estimates, the Vector components, the measured HI & Rod heights, as well as the GEOID 'N' value in that area.
GIGO
Loyal
thanks Loyal and Shawn. I am pretty sure the vertical error is coming from the Network. I am on the coast and the network results vertically are generally less than optimal. The horizontal has given great results so far.
Have either of you had experience setting Carlson up with an LDP?
I have ZERO experience with Carlson Drafting software.
BUT...
I would ASSUME that once you import the [LDP] GRID Coordinates into it, then GRID=GRID regardless of the underlying projection parameters (at least that's the way that AutoCad seems to work).
Obviously IF one wants to transform a drawing from an LDP to SPC or UTM (or another LDP), then the projection parameters (and maybe even the datum) of each projection would of course come into play.
Again...ASSUMING that “everything” is in [say] NAD83(2011), then this SHOULD be a simple process.
Loyal
For Good Vertical You Want To Be Within The Network
That way the data is interpolated.
When you are outside the network, i.e. along the coast, data is extrapolated.
Assume 3 base points, +/- elevation, inside the net you are less than the +/-es.
Ouside the net you can easily be greater than the +/-es. I consider it that you are warping your data.
Rather than using the net, independant solutions from each base to the rover are more accurate. I am aware that some nets allow one base solutions to a point. Some do it sequentially but some newer systems can do it simultaneously.
Paul in PA
For Good Vertical You Want To Be Within The Network
Paul, the way the underlying network is setup, I am actually inside the box, however the verticals here seem to be less than ideal. On this project verticals are not critical, I do not use regular RTK but I believe I can achieve good vertical results with static methods on my control points.
For Good Vertical You Want To Be Within The Network
> ... the verticals here seem to be less than ideal....
Go ahead and project your data onto a state plane grid. It should be easy to switch the projection in your dc. I think you will see that it has no effect on verticals, one way or the other.
For Good Vertical You Want To Be Within The Network
Along a coast the verticals will always have a tendency to be iffy because there are no data points in the water. You are actually on the very edge of a model. The GRAV-D Project is collecting aerial gravity data over water in an effort to extend the geoid models beyond dry land.
They are hoping for 2020 ...
Yes, I use Carlson with LDP's in the field (SurvCE 2.x) and in the office (Survey 2013).
Carlson works, but their explanations are crappy.
The parameters in Survey are meters always and DMS.
In SurvCE the parameters are meters and D.dd.
If you build your LDP in Survey, you can save it and upload it as a CSL or UDP to SurvCE. It's a good way to go. SurvNET will read a UDP, so it' a good way to go if you use SurvNET.
Coordinate transformations using LDP are doable in Carlson Survey IF you use Lat/Long as an intermediate step. So, if you want to go to State Plane from your LDP, you set up the transformation to go from your LDP to Lat Long. Then go from Lat Long to SPC. You can also do this in reverse.
To set up the LDP in Carlson Survey go to Settings>Drawing Setup. Click "Define Projection". You don't have to save the projection you build, but it's handy for using in SurvCE or SurvNET. I have several projections that aren't saved individually but the appear in the projection list. In the Add User Defined Projection section, you enter a name of your custom projection, Datum (which Carlson treats WGS84 and NAD83 as equivalent - which is fine for this purpose). Select your projection type. For Lambert Single Parallel and Transverse Mercator, enter the Central Meridian (aka Longitude of origin)giving care to using the "-" if it's a West Longitude, Latitude of Origin, your custom scale factor, the false E and N IN METERS. It's a very good idea to test your projection, but inversing the SPC values of a couple of points and inversing the same points in your projection and applying the proper mapping angle and CSF to the inverse.
Got to go. I'll try to add more later. If you have questions throw them out there.
For Good Vertical You Want To Be Within The Network
The NC VRS is a great tool , but I can tell you Verticals are not great . I was getting mixed results on most of my projects and have gone back to using OPUS to get Grid on the job , Then I set up for local Static or RTK with Rover and Base .
Shawn i appreciate your help, can you explain how to do the transformation from LDP to state plane in Carlson? It seems really simple in TBC, I just select the coordinate system and it automatically performs the transformation...
For Good Vertical You Want To Be Within The Network
that's another area I am iffy on, going back and forth between projections in data collectors. I use Survey Controller for my GPS, if you have any experience with that.
For Good Vertical You Want To Be Within The Network
I do. You can do it. But just to be sure, back up your data first.
> Shawn i appreciate your help, can you explain how to do the transformation from LDP to state plane in Carlson? It seems really simple in TBC, I just select the coordinate system and it automatically performs the transformation...
The way I go about it is:
Create a copy of my CRD file with a letter change to the file name. I use "G" for "grid", you could use "SPC". So my job number M13001.crd becomes M13001G.crd. I open another drawing (it doesn't matter what this drawing is, just a blank drawing) and set my current coordinate file to the copy (M13001G.crd). If you don't do this in another drawing, your screen points will move from your LDP to LLH to SPC as you transform. Opening a different drawing file will keep this from happening. I then use the coordinate transformation routine to transform from Grid to Lat Long. From the pull-down, I select "More Pre-Defined/User-Defined" where I select my LDP. For destination, I select WGS84, Degrees, Minutes, Seconds, and select "OK". After that I perform another transformation from WGS84 to my selected State Plane Zone.
It sounds complicated, and I suppose it is a bit, but after you do this a time or two, it becomes very automatic. You end up with a CRD file in your LDP and a CRD file in your SPC with this method. If you add a coordinate to either file, you will need to go through the procedure again to update the other with the new coordinate. I generally wait until all of my calculations are completed before I do this, but again, it isn't that big of a deal, so it's not too much trouble if I add to my LDP file, overwrite the SPC file, and redo the transformation. Or if I have an SPC I want to bring into my LDP file, to enter it in the SPC file and go through the process backwards (make copy of SPC file with new name, transform from SPC to Lat Long to LDP).
One nifty thing about Carlson and LDP is once you set up the LDP you can output your drawing straight from dwg(LDP) to Google Earth KMZ or KML.
> Yes, I use Carlson with LDP's in the field (SurvCE 2.x) and in the office (Survey 2013).
>
> Carlson works, but their explanations are crappy.
>
> The parameters in Survey are meters always and DMS.
> In SurvCE the parameters are meters and D.dd.
>
> If you build your LDP in Survey, you can save it and upload it as a CSL or UDP to SurvCE. It's a good way to go. SurvNET will read a UDP, so it' a good way to go if you use SurvNET.
>
> Coordinate transformations using LDP are doable in Carlson Survey IF you use Lat/Long as an intermediate step. So, if you want to go to State Plane from your LDP, you set up the transformation to go from your LDP to Lat Long. Then go from Lat Long to SPC. You can also do this in reverse.
>
> To set up the LDP in Carlson Survey go to Settings>Drawing Setup. Click "Define Projection". You don't have to save the projection you build, but it's handy for using in SurvCE or SurvNET. I have several projections that aren't saved individually but the appear in the projection list. In the Add User Defined Projection section, you enter a name of your custom projection, Datum (which Carlson treats WGS84 and NAD83 as equivalent - which is fine for this purpose). Select your projection type. For Lambert Single Parallel and Transverse Mercator, enter the Central Meridian (aka Longitude of origin)giving care to using the "-" if it's a West Longitude, Latitude of Origin, your custom scale factor, the false E and N IN METERS. It's a very good idea to test your projection, but inversing the SPC values of a couple of points and inversing the same points in your projection and applying the proper mapping angle and CSF to the inverse.
>
> Got to go. I'll try to add more later. If you have questions throw them out there.
I have read your magazine articles on LDP's as well as followed the threads in this forum. I am attempting to create a UDP file with Carlson Survey 2014 for use with SurvCE. I have had success with both Lambert and Transverse Mercator Projections, but the Oblique Mercator is giving wildly wrong answers in the Northing when tested. Since we are "fitting" this projection to a platted bearing, it is important I be able to insert a skew angle.
Has anyone else had this problem? Try it out. I am going to try to contact Carlson, but right now it looks like a bug in the programming