Chapter 8 - Survey Data Collection Standards
Chapters
Training Materials
8.1 Planimetrics
The mapping process involves gathering data about the shape of the land and the location of features on, above and below the surface. From this data digital Deliverables are prepared to represent existing site conditions at the time of the survey. See Chapter 10 for the deliverable requirements. All surface topography, elevations, surface utility locations, and drainage, both surface and underground will be located with feature IDs as outlined in Chapter 4.3.4 Planimetrics. The electronic files developed for this section serve as a base for design.
| Item | Tolerance |
|---|---|
| Planimetric point - soft ground measurements recorded at | nearest 0.01" |
| Planimetric point -soft ground accumulated S.E. (2σ) | 0.10" |
| Planimetric point - hard surface measurements recorded at | nearest 0.01" |
| Planimetric point - hard surface accumulated S.E. (2σ) | 0.05" |
| Instrument/target H.I. measured to | nearest 0.01" |
| Instrument/target centering error | 0.02" |
| Distance to shots on hard surfaces- maximum | 650" |
| Distance to all other shots-maximum | 1300" |
| Max difference (X,Y,Z) between original and check shots | 0.05" |
Table 8.1.1 Summary of Standard Mapping Parameters
8.2 Terrain Elevations
Elevation data will be obtained as needed for project design, quantity computations and drainage studies. As a general rule, there should not be more than 100 feet between random shots to obtain elevations. Elevations of ground surfaces (dirt) should be recorded to the nearest 0.01 feet. The accumulated standard error for ground elevations should be no greater than 0.10 feet. All hard surfaced roads, curbs and sidewalks and water surface elevations must be recorded to the nearest 0.01 feet. The relative error between adjacent elevations must have an accumulated standard error of no more than 0.05 feet for hard surface shots. If the total station method is used, instrument heights and target heights must be measured to the nearest 0.01 feet and recorded. Sights must be taken to targets on prisms. Distances for shots taken to determine hard surface elevations must not exceed 650 feet. No distances for any topographic data collection may exceed 1300 feet.
When doing mapping field work, all horizontal and vertical control must be checked into as random shots with the designation recorded. The difference between mapping check coordinates and previously adjusted coordinates must not exceed 0.05 feet in x, y or z.
When requested, the surveyor must produce an existing conditions model of the project site. Break lines and high/low points must be used to make the model an accurate representation of the shape of the ground. In many cases cross sections at a set interval will not yield an accurate representation of the terrain. Careful attention should be given to observation of the terrain as it breaks in the field. Building interiors must be excluded from the DTM. The surveyor must examine the model for accuracy and completeness. An existing conditions model of the site will be produced from this survey data. The surveyor must certify the accuracy of the existing conditions model in the Surveyor's Report Certification.
When terrain elevations are obtained to supplement photogrammetric or LiDAR mapping, both the ground survey and the photo / LiDAR mapping must use the same horizontal and vertical control. A digital terrain model and contour map must be produced as described above but limited to hard surface observations and obscured areas. Any DTM assembled to supplement photo / LiDAR mapping under this section will be identified with file naming consistent with the requirements set forth in Chapter 10 - Deliverables
8.3 RTK GNSS
8.3.1 General
Real Time Kinematic (RTK) Positioning Techniques:
- RTK GNSS surveys consist of a data transfer link and at least one GNSS unit set over a known (Base/Reference/MDOT CORS) station which remains stationary, while the rover(s) unit(s) are moved from station to station. In a RTK survey, shots are taken "radially" from a fixed base station to a rover unit. A delta X, delta Y, and delta Z are produced from the base station which are then transferred to the rover unit. Occupation time at rover station(s) range(s) from generally a few seconds to a few minutes depending on the work being performed.
RTK GNSS is not the tool for everything.
The following is a reasonable list of acceptable RTK applications:
- Supplemental control for engineering and construction surveys.
- Portions of photogrammetric control targets surveys. (Can be used for horizontal control and a portion of vertical control, mainline of the photo control project will still need to be leveled.)
- Collection of topographic and planimetric data. (Except hard surface shots)
- Construction surveys / Staking. (Except for major structures)
- Right-of-Way surveys
- Section breakdown and government corner surveys.
- GIS type surveys. (Structure inventories etc...)
- Environmental type surveys. (Wetland boundaries location and delineation etc.)
Reconnaissance:
- Numerous factors affect the performance of GNSS. Care and diligence needs to be observed when selecting a project for use with RTK GNSS positioning techniques. Listed are some of the factors that affect the quality of the final coordinates generated by RTK GNSS.
- Visibility of the horizon. (Obstructions above 15 degrees.)
- Instrument setup error. (Height reading blunders, improper leveling etc...)
- Improper mission planning. (Poor satellite geometry.)
- Inadequate observation times.
- Improper initialization of receivers. (Wrong ambiguity resolution.)
- Type of terrain could affect the communication links.
- Radio frequency interference. (Can be checked by using a scanner of the same freq.)
- Instrument calibration. (Bubbles adjusted on rods and tripods.)
- Improper field survey procedures.
- With proper planning, some obstructions near a GNSS station may be acceptable.
Equipment Requirements:
- Geodetic grade receiver capable of logging observables concurrently while broadcasting / receiving.
- Must be capable of containing the following:
- A map projection. (Lambert Conformal)
- Ellipsoidal model. (GRS80 or WGS84)
- Geoid model. (Must be Geoid 12A or later.)
- Must be capable of performing a 3D Helmert transformation.
- Dual frequency GPS receivers L1/L2 capable of OTF (On The Fly) initialization. These receivers can tolerate loss of lock since they are capable of solving integer ambiguities instantly. All equipment must be properly maintained and regularly checked for accuracy.
- Level vials, optical plummets, and collimators shall be calibrated at the beginning and end of each project.
- If the survey duration exceeds a week, the calibrations shall be conducted on a weekly basis.
Antenna Height Measurements:
- Blunders in the measurement of antenna heights are the most common source error in GPS surveys. All GPS surveys are performed in 3D even if the final result is a 2D position. The height measurements determine the height from the survey monument to the antenna electrical phase center. Keep in mind that the GPS manufactures software generally allows for a direct height measurement to be entered. If mixing receiver and processing software, reduce all the antenna heights to the Antenna Reference Plane (A.R.P.) also known as Mechanical reference plane. (M.R.P.) The A.R.P. is generally the lowest mechanical surface on the antenna itself. A.R.P. diagrams for your particular antenna can be obtained from the National Geodetic Survey website.
Satellite Geometry:
Satellite Geometry affects both horizontal and vertical coordinates in GNSS/RTK type surveys. For RTK type surveys, the following factors are to be considered (See appended table):
- Number of common satellites at the base and rover unit.
- Satellite elevation mask
- PDOP (Positional Dilution of Precision)
- GDOP (Geometric Dilution of Precision)
- VDOP (Vertical Dilution of Precision)
Type and location of Control Monuments:
Primary project control monuments and RTK control monuments are required to:
- Positioned relative to the Michigan Spatial Reference Network (MSRN) in it's active coordinate system (MDOT CORS).
- Be leveled using conventional techniques. These techniques for leveling will employ current MDOT standards for conventional leveling.
- Have elevations based on NAVD 88.
- Positioned so that RTK check monuments are located along the project path and can be checked at regular intervals.
- Have a clear view of the horizon above 15 degrees.
- Located on stable ground.
- Readily accessible.
- Located off the traveled portion of road but within the road right of way, or located on public property.
- Set in anticipation of any future tree or shrub growth.
- Set in order to avoid tall structures which could cause multipath.
- Set to avoid radio towers, power transmission lines, and other sources of RF interference.
- Set the points so they are intervisble for use with conventional survey methods.
- Set at a location which ensures the safety of surveyors and others.
- RTK control monuments must be set and witnessed in the same manner as intermediate control as stated in these Standards of Practice.
- An RTK control monument is a monument used to control a survey that utilizes RTK methodology. The station must have either horizontal coordinates, a height, or both. Primary Control monuments can also serve as an RTK control monument. However, primary control monuments CAN NOT be set using RTK methodology.
8.3.2 Field Procedure
Proper field procedure produces a successful RTK survey. Problems will occur if proper field procedures are not employed during the course of an RTK survey. MDOT realizes error resolution is a professional judgment call. Procedures for resolving errors must be discussed in the work plan. If a conflict between the accepted procedure and its application exists, contact the MDOT Survey Consultant Project Manager or the MDOT Region Surveyor.
- A base station should occupy a Primary Control monument with known coordinates. A direct link to a CORS site or base station location over an Intermediate Control point is acceptable with permission of the MDOT Survey Consultant Project Manager or the MDOT Region Surveyor.
- Transformation sets are only allowed when trying to match surveys which do not have Michigan State Plane Coordinates. Rotations should be specified in the Surveyors Report completely with Δx, Δy, rotation angle and scale.
- A check shot must be observed on Intermediate Control by the rover unit(s) immediately after the base station is set up and before the base station is taken down.
- A minimum of 5 satellites must be observed at the base and the rover(s).
- The second occupation of a new station must have a maximum difference in coordinates from the first occupation of 0.05ft.
- Two independent vectors must be used to verify the check shots. Vectors can be generated from CORS within 9 miles or on-site base stations.
- At least 5 percent or 5 shots, whichever is greater, must be taken on hard surface so the points that can be re-visited and re-observed as check shots the same day. Check shots must be spaced uniformly throughout the area, not grouped together, and re-observed from the second base.
- Check shots to the re-visited hard surface points must agree to within 0.05ft.
- The re-visited points must be named such that they have a unique name but can be correlated to the initial point. For instance, LL30456 becomes CHK30456.
- A minimum of 30 minutes between the original shot and the check shot is required.
- A table must be created on a daily basis comparing the original shot with the check shot. Table's 8.3.2.1 and 8.2.2.2 show examples.
- At the end of the day, the RINEX file from the base station should be submitted to OPUS.
Table 8.3.2.1 - Check Shots per Distance
| 0.5 miles | 1 mile | 2 miles | |
|---|---|---|---|
| 2 lane roadway with 5 observations per section | |||
| 50" cross sections - shots/checks | 264/13 | 528/26 | 1056/53 |
| 100" cross sections - shots/checks | 132/7 | 264/13 | 528/26 |
| 200" cross sections - shots/checks | 66/5 | 132/7 | 264/13 |
Table 8.3.2.2 - Check Shots Comparrison Sheet
| Point # | Initial Observation | Point # | Check | Delta | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| X | Y | Z | X | Y | Z | dX | dY | dZ | ||||||||
| CP 100 | 428421.294 | 13039502.124 | 885.787 | CHK 100 | 428421.282 | 13039502.135 | 885.775 | -0.012 | 0.011 | -0.012 | ||||||
| CP 101 | 427938.112 | 13039398.012 | 888.034 | CHK 101 | 427938.124 | 13039398.017 | 888.046 | 0.012 | 0.005 | 0.012 | ||||||
8.3.3 OPUS Procedure
- OPUS can be used for establishing the horizontal datum within the project area at a minimum of two locations. The intent is to have OPUS positions at strategic locations throughout the project to be held fixed in the processing and adjustment of the project control network.
Observation Procedures
- Antenna Height measurement at the beginning and end of the observation session.
- Amount of time will be dependent on the density of MSRN stations in the vicinity of the project. Observation times even in the ideal configuration of stations shall not be less than 2 hours.
Deliverables
- An observation Log sheet showing the following:
- Manufacturer Make and Model of the Antenna and GPS receiver used.
- The corresponding NGS antenna definition for the Antenna used.
- Direct antenna height readings taken and the location where taken.
- A reduction of the direct antenna height reading to the ARP (Antenna Reference Plane)
- OPUS extended output:
- Output must have peak to peak Errors of less than 2 cm (0.06 feet)
- IGS Rapid or precise orbits must be used. The use of Ultra Rapid Orbit is not acceptable.
- Overall RMS of Observation must be under 2 cm (0.06 feet)
- 95% or greater of the ambiguities must be fixed.
- 90% or greater of the observations must be used.
- All reference stations used as control must be MSRN Stations. If not possible, contact the MDOT Survey Consultant Project Manager or the MDOT Region Surveyor.
- State plane coordinates for the point must all be displayed.
- The raw data file from the GPS receiver in its native format and the RINEX converted file must be submitted.
- The RINEX files for the MSRN stations used by OPUS must also be provided, these files are available from https://mdotcors.org
- All of the files must be submitted in electronic format; in addition a hard copy of the OPUS output and the observation sheet mus
- Solutions are not to be used for Ellipsoidal heights unless 3 independent observations of 5.5 hour sessions are employed.
- For groups of control points spaced less than 1500 feet apart, the following procedures must be followed:
- All of the points may be submitted to OPUS.
- The baselines between the groups of points must be calculated using conventional post processing techniques, using the OPUS derived values as a check.
- All other positioning and monumentation requirements as specified by the MDOT survey manual remain in effect.
- An independent manual conversion of the metric SPC to international feet must be made and compared to the OPUS computation.
8.5 Radial/Conventional
- TPS (Terrestrial Positioning System) or more commonly known as Total Station is an optical instrument that measures angles and distances. Vertical accuracy diminishes the further away the target moves from the instrument.
- Minimum equipment requirements:
- Total Station - A survey grade total station with a minimum angular accuracy of 3 seconds per ISO 17123-3 and a minimum EDM accuracy of 2 millimeters + 2 parts per million per ISO 17123-4
- Procedure
- Backsight distances must not exceed 1500 feet
- Foresight distances must not exceed 600 feet
- Horizontal distance checks must not exceed 0.03 foot
- A minimum of 1 benchmarks used to establish vertical orientation
- A minimum of 1 benchmark used to verify vertical orientation
- Vertical orientation and verification must not exceed 0.01 foot
- The first and last measurements of a setup will be check shots and must be recorded in the raw data
- Survey field notes must be taken and all changes in rod height must be recorded
8.6 Utilities
Public safety and good design practice requires that the design engineer know the location of utilities in the project area. A listing of companies with utilities in the area should be furnished to the consultant from the MDOT Utility Engineer or obtained via the MISSDIG Design Ticket Program. The consultant should validate the accuracy of the contact list and update if necessary.
The surveyor must locate and identify all visible utilities. Before starting the survey, the surveyor must determine whether the designer requires all utilities to be located or just those visible above the ground. All utilities must be related to the coordinate system of the project and shown on the topographic map.
The surveyor must provide, if requested, a list of utilities with installations located in the project area, noting address, phone number and contact person for each utility.
If underground sanitary (gravity flow) or storm sewer information is necessary, the point number, station & offset, composition, size, and invert elevation of each pipe at each manhole must be provided in a Utility Inventory Spreadsheet and connectivity must be plotted. It may be necessary to prepare separate plots to show connectivity. Plots of underground utilities may be combined if not too cluttered.
8.7 Drainage
8.7.1 Purpose
When required to collect drainage information during the design survey, surface and underground drainage information is assembled by the surveyor. The surveyor must contact the local officials to obtain plans of any drains crossing the project and to inquire about any known drainage problems within the project area. The surveyor must report any observed drainage problems and provide photographs of the problem areas. Any information freely offered by the residents relating to potential drainage issues should also be reported.
8.7.2 Procedure
The composition, size and invert elevation of each pipe at each drainage structure is required for design of improvements in critical areas. The construction material and condition of each structure and connecting pipe must be fully described. Connections to drainage structures may be determined as outlined in the scope. Culvert descriptions must include material type, size, and end section treatment, invert and flowline elevation, if different. Notes and photographs detailing the general condition, including deterioration, pipe alignment and infiltration must also be included. The above information must be detailed in the Structure Inventory Spreadsheet.
The location of all drainage structures at the center of cover and center of the bottom of structure as well as connectivity of drainage pipes are to be plotted. See Figure 8.6.1 and Figure 8.6.2 for examples of the described locations. Outlet structures must be noted with the invert elevation. It may be necessary to prepare separate plots to show underground storm drain systems. Plans and maps obtained from local officials are to be included with the notes. Reports from these officials regarding drainage problems and the surveyor's observations will be documented in a separate drainage report.
Confined space entry is restricted to personnel with proper training and equipment when necessary. Refer to Confined Space Entry. Payment for confined space entry will not be made unless specified in the price proposal.
List of Requirements:
- Create an index of all photos
- If a picture is captured and it corresponds to a measured survey point the name of the picture must be named the same as the survey point number.
- If a picture does not directly correspond to a survey point the images must be named with a description of what is represented in the picture. For example (Structure B01 of 12345 Looking west.jpg)s taken during the survey must be named to correlate to the point number
- All pictures must be zipped into one or more .zip file(s) depending on the size of the files.
- The file size must not exceed 100MB.
- See Chapter 10 for standard naming convention.
- The bottom of the center of the structure must be located and indicated in the .dgn with the BOS feature code. There are 5 options for BOS which are size specific to represent the appropriate structure size. The positional accuracy for the BOS shot should be approximately 1 foot (horizontal).
- The "Z" location of each invert in a structure must be represented at the correct elevation, coincident with the "X", "Y" location of the BOS shot.
- 1. Attribution of the invert point should be standardized as follows:
- Direction_Diam(in)
- Example:
- 'N 12IN'
- 'NE 14IN'
- 2. Utilize the appropriate material specific feature code to represent the pipe (example : CMP, RCP)
- 3. In instances where the pipe material is unknown, utilize the INV feature code to represent the invert.
- Feature code CB represents a square catch basin. The insertion point, and corresponding location of the field observation, should be at the center of the casting. The flow line should continue to be located as part of the GUT linear feature.
- Feature code CBR represents a round catch basin, or yard basin.
| Feature Code | Description | Cell | Notes |
|---|---|---|---|
| BOS | Bottom of Structure, generic, when structure size is unknown or larger than 6' in diameter. Placea 4' diameter structure. | NoID_StrucBot_Ex_048in | Located at center of bottom of structure. |
| BOSTWO | Bottom of 2' structure | NoID_StrucBot_Ex_024in | |
| BOSFOUR | Bottom of 4' structure | NoID_StrucBot_Ex_048in | |
| BOSFIVE | Bottom of 5' structure | NoID_StrucBot_Ex_060in | |
| BOSSIX | Bottom of 6' structure | NoID_StrucBot_Ex_072in |
Figure 8.7.3: BOS Feature Code Table