Thursday, September 15, 2016

Setting up a Leica CS15 Controller to use LDP parameters

Mike Caniglia with TD2 and Dan Kahm with A&D have taken the time to create how-to files to create and import LDP parameters for the Leica CS15 Controller. The Create Parameter how-to is here and the Import Parameter how-to is here. The TRFSET.DAT file which contains parameters for all the counties except Hall, Platte and Lancaster may be downloaded here.

Thanks to both for taking the time to do all this.

Thursday, July 21, 2016

Setting up your SurvCE data collector to work in an LDP

As most of us aren't used to getting set up to work strictly in an LDP system, there's a number of things that maybe aren't especially clear about how to get Carlson set up.  We're used to using a ground-to-grid scale, or maybe a localization file.

The end-goal of an LDP is that neither a scale nor a localization is necessary.  The only conversion is from Lat/Long to local North/East.  Scale, rotation and coordinate conversion is all handled solely by the projection parameters.

A quick how-to for getting set up and working in the LDP is here.

Wednesday, June 29, 2016

SurvCE 5.0 - adding new projections

The linked documents will show you how to add the LDP parameters to SurveCE V 5.01.

A Lambert Conformal Conic 1 SP for Adams is here.
A Transverse Merecator for Antelope is here.

You can also download the parameter files using the "SurvCE parameter files" link. The files can then be loaded into your data collector and Carlson Survey desktop.

The actual pages from the SurveCE manual are here.

A brief article from Mircea Neacsu explaining the difference between WGS84 and GRS80 is here. The article is dated but the information is still relevant.

I would appreciate any help with posting similar information for Leica, Trimble, Topcon, Sokkia, Spectra, etc. Contact me if you can help.


Tuesday, June 28, 2016

Online Database of section corner locations

Update: We actually went ahead and did it. Go here to upload and download section corner latitudes and longitudes.

Once we all have the ability to have a single coordinate for every point in a county by eliminating the modified state plane calculations is it time to have a single database of locations available to everyone?

Lancaster and Sarpy counties have coordinates at their section corners that are publicly available in some way, shape, manner or form.  However, they don't accept positions from surveyors.

I would suggest that (as we transition from autonomous position to valid NAD83(2011) positions) we create a statewide online database of corner positions.  We all currently punch in the surrounding surveys to generate "search" coordinates so a single database online wouldn't be much different.

I would propose submitting latitude, longitude and height, as well as a description for each corner located, as long as the corner is correctly tied to 83(11) and has a long enough occupation time to give a good confidence level.

My thought would be to name the corners something like this:
TTRRNDX where the TT is township North (01-32), RR is range West (01-55) with ranges East having an add of 70.  So, Range 1 East would be 71, 14 East is 84, etc.
The NDX is an index number that is similar to the systems Kansas and Colorado use.
Kansas has a requirement to file corner ties that conform to their standards.
Here's their website that begins the process to see ties.  In the upper area put in 13 South, 25 East and it shows the number of corner records in a portion of Kansas City.  The recovery form is here.
Colorado is a little different than Kansas.  Their numbering is the same but letters run from bottom to top A-Z.
Here's an example of the Colorado recovery report form, and here's the index they use.

My thought is to use letter-number-number similar to Kansas.  The Northwest Corner of the township would be A01.  Here is the index sheet I currently use when I submit corner reports (with my surveys) to the repository.  A sample of my corner report at the repository is here.

For example, the center of section 16, T5N, R6W would be 0506L11
The West 1/16 Corner for sections 25 and 36, T1N, R18E would be 0188V22

All standard sixteenth corners can be indexed this way.

Other ideas?

We need your help

We rely on your help for testing. By “testing” we mean you submitting information we can drop into the spreadsheets we use to calculate distortion or you installing a county parameter file in your data collector and checking on known points, to suggest a couple of ways.

To date we have received information, usually section corners, from Douglas, Sarpy, Cass, Platte, Hall, Hamilton, Richardson, Nemaha, Johnson and Pawnee counties. We have also received spot information from around the state and a few surveyors have loaded the parameter files for field work. So far there haven’t been any big issues and things seem to be going as expected. In the counties mentioned above all the submitted data has fit very well using the LDP county parameters.

If you would like to help let us know. We need information in latitude\longitude\HAE or state plane with elevations. An easy way would be for you to send us your raw files. We combine them all into one big file and strip out the information we need county by county.


Contact us if you are interested and thanks for your consideration. 

Monday, June 27, 2016

Getting Started for RTK users

One of the best reasons to use an LDP is that there's only one set of coordinates for each point in the county.  No scale factors, no localizations.  Once the files are set up and the RTK base is on a point with valid coordinates, all points measured and stored are related to each other by ground distance and angle.

No more shooting the same point over and over in different projects with different North/East coordinates.

To get started, a brief how-to (fieldwork setup and procedures) is located here
This is primarily for RTK single base users.  RTN will be addressed in later posts but the point numbering and occupation times are still valid for RTN as well as RTK.

Saturday, June 25, 2016

County Low Distortion Parameters

The low distortion projection parameters for each county may be found here. The counties of Lancaster, Platte and Hall have existing projections. Contact those counties for information. 

Please let us know if other counties are using existing projections so we can update the list.

Should you decide to use the low distortion parameters please let us know how they worked for you. 

Thanks.

County Grid Parameter Design

Objective:
The project was undertaken by Brent Jorgensen, NE LS-621, and Steve Cobb, NE LS-412, to create projection zones, preferably at the county level, that minimized the distortion between grid and ground measurement. The low distortion projection parameters would eliminate the need for constant calibration\localization of GPS units prior to field work. 

Distortion Issues:
Distances measured on the ground and then projected on to any designed grid are subject to distortion due to elevation and curvature along the ellipsoid from the point to the standard parallel or central meridian in a Lambert or Transverse Mercator projection respectively.

Design Method:

Elevation:
The 30 meter, 7.5 minute topographic quadrangle DEM files, available from the Nebraska Department of Natural Resources, were used to create a state coverage. The point information was extracted at a 25% level leaving approximately 170 points per section for evaluation. The DEM files are in UTM, ortho height format.
The DEM files were combined by UTM range, converted to Nebraska State Plane 2600, HAE format. The three converted ranges were combined to create a statewide coverage in State Plane 2600 format.
A GIS program was used to overlay county boundaries over the elevation coverage and extract elevation files on a county by county basis.

Projection and Parameter Determination:
Each county elevation file was converted to a geographic projection (Lat\Long\HAE) and read by custom software which reported the average distortion, created by both elevation and curvature, of each latitude and longitude in the county on a minute by minute basis. Latitudes and longitudes with the lowest averages were candidates for either standard parallels or central meridians. The selected latitude, longitude or county configuration determined the projection. The origins were established within the county and the false northings and eastings were determined to avoid any negative coordinates within the county.
Note: The designers were aware of suggestions that a standard parallel or central meridian should be centered in the projection area. The designers felt this was counterproductive and opted to select locations which minimized distortion.

Scale Factor:
An initial scale factor was suggested by the custom software used in the previous section. A spreadsheet was used to fine tune the scale factor by observing the PPM (parts per million) spread over the county. The spreads were listed in 5 PPM increments from -25 PPM to +25 PPM. The scale factor was adjusted to center the maximum percentages near the middle of the spread. The design goal to keep 50% of the county within the ±5 PPM range and 85% of the county within the ±10 PPM range was met in many of the smaller counties.
In the larger counties and\or those with greater elevation change such a goal was difficult to achieve yet ±15 PPM was still attainable in many circumstances.

PPM Reference:

PPM per mile:
5ppm\0.03’
10ppm\0.05
15ppm\0.8’
20ppm\0.11’
25ppm\0.13’
Testing:


The low distortion projection project is a work in progress. Help is requested in verifying the validity of the parameters. If you want to help please contact Steve Cobb at (402) 471-2566 or steven.cobb@nebraska.gov.