1 / 58

Pipelines and Mapping

Pipelines and Mapping. How ILI, GPS and Inertial Measurement Work in the Real World 11/14/2013. Earth Measurement. Geography describes attributes of features on the Earth’s Surface Cartography presents features in a way that facilitates understanding

agnes
Download Presentation

Pipelines and Mapping

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Pipelines and Mapping How ILI, GPS and Inertial Measurement Work in the Real World 11/14/2013

  2. Earth Measurement • Geography describes attributes of features on the Earth’s Surface • Cartography presents features in a way that facilitates understanding • Geodesy describes where things really are on the Earth as an entirety

  3. Flat Earth • Navigation was inexact, charts were easy to store • Good for showing relationships between features

  4. The Sphere • Eratosthenes used camel caravans as a unit of measurement to determine the circumference of the Earth

  5. The Ellipsoid • Sir Isaac Newton determined that the earth must be an ellipsoid. • Effect of gravity and the Earth’s rotation. • Flattened at the poles and bulges at the equator.

  6. Geographic Coordinates • Longitude is determined by time offset from the Prime Meridian • Latitude is calculated by determining the perpendicular to the ellipsoid surface, then finding the perpendicular to it and determining the angle it forms with the plane of the equator

  7. Spherical vs Ellipsoid … (oops) This is not really halfway between the north pole and the equator – that point would be about 10 miles north of this sign.

  8. The Geoid • Gauss described the effects of gravity on mapping, and the datum (and geoid) was born

  9. The concept of the “equipotential surface” and Mean Sea Level • North Atlantic oscillation as an example • Tunnel through the Alps as an example • Bougeur correction • LaPlacian correction • Matching an ellipsoid to a datum

  10. Example of a datum shift

  11. PROJECTIONS Latitude/Longitude (no projection) - Only spatial data representation that can be truly geodetically correct. Ideal for GIS data that is not being used for visualization, or for large GIS databases, or for GIS software that can reproject to any chosen projection. Projections - Best applied to smaller geographic areas

  12. Projection Types • Cylindrical Transverse Oblique • Conic • Azimuthal (Planar) • Pseudo-Cylindrical • Others

  13. Projection Attributes • Conformality (Shapes and “local” direction) • Area • Reliability of Scale • Direction

  14. Named Projections • There are several hundred named projections, and an infinite number of possible projections, but for the most part there are only a very few important projections in use. Because the reliability of attributes changes depending upon the projection, it is important to understand how and when they are used.

  15. Common Projections • Mercator - A conformal, cylindrical projection that is reliable for scale in a very limited area on either side of its equatorial axis. Usually used in very large areas (very small scale) maps, such as entire world. • Albers Equal Area - A non-conformal, conic equal area projection that has the least distortion of scale for large areas. Used in national maps, maps of Alaska, maps of Hawaii, and maps of North America.

  16. Common Projections • Transverse Mercator - A conformal, cylindrical projection where the cylinder is “set on its side” so that a degree of longitude forms its “equator”. Reliability of scale is limited in a longitudinal direction, and there is a scaling factor for latitude. Used for mapping areas predominantly North-South in extent and limited to a few degrees of longitude.

  17. Common Projections • Universal Transverse Mercator (UTM) A system to identify a series of 6 degree strips around the world, each uniquely numbered with a UTM zone number. Very common when a series of maps are being produced and political boundaries are unimportant in defining map extents.

  18. Common Projections • Oblique Mercator - A conformal, cylindrical projection where the cylinder is offset from latitude and longitude. Used when the area to be covered in mapping forms a significant angle when compared to latitude or longitude lines, and where the total area on either side of the resulting “great circle” will be small. Used in the U.S. State Plane Coordinate System to map the Alaska Panhandle.

  19. Common Projections • Lambert Conformal Conic - As the name indicates, a conformal conic projection. A very common projection used when the area to be mapped is primarily East-West in extent, and very limited in a North-South direction. Normally used on medium scale maps (1:250,000 - 1:1,000,000).

  20. Other Projections • Polyconic (Now defunct) • Azimuthal Equidistant • Bipolar Oblique

  21. State Plane Coordinate System • The United States has been broken into a series of zones, totally dependent upon political boundaries. Each of those zones has a very clearly defined set of projection parameters. The projection type for each zone is dependent upon whether the zone is primarily east-west (Lambert), north-south (Transverse Mercator), or offset (Oblique Mercator).

  22. State Plane Coordinate System • Originally designed by USCGS to limit distortion of scale • The information about the system changes based upon the reference ellipsoid

  23. IMPORTANT FACTS !!! • The Earth is NOT flat! • No projection maintains scale across an entire area • No projection is the “right” choice for every project • Every projection has a potential “gotcha” • The State Plane Coordinate System is not a projection.

  24. Inertial Measurement • In Marvin Escher’s Relativity there are 3 separate gravity axes. It makes sense and is confusing at the same time. An IMU works much the same way.

  25. How Gyroscopes Behave Illustration from Wikipedia

  26. Inertial Measurement • There are two reference frames for inertial measurement – gravity and the inertial reference frame. These are the geoid and the gyroscope’s position relative to space.

  27. Latitude deflections

  28. Longitude deflections

  29. Example: • Gravity Recovery and Climate Experiment (GRACE) • 2 satellites at a known distance from each other with Doppler ranging to determine orbital changes

  30. EGM2008

  31. Time • Time is a critical element of modern measurement. Reference frames change over time. GNSS measurements are based on time. Time is also relative.

  32. The North American Plate

  33. Tracking station drift

  34. The IMU Reference Frames

  35. Example of “Drift”

  36. Full view of “Drift”

  37. The previous 2 slides illustrate what happens when a commercial software package takes IMU data at “face value”. This was a 254 foot test loop using 6 inch pipe that was created to illustrate what happens with different approaches • The next slide represents what happens when software is written that takes context into consideration. The tips of each “tack” represent where the software believed the IMU to be. There are light green tacks that mark actual locations. Calculated locations are within 4.5 inches of their actual location (within diameter of the pipe.)

  38. What it really looks like

  39. IMU Measurement • Although the Earth is rotating beneath the IMU, and although measurement drift is occurring, it is possible to get very accurate maps from a smart pig equipped with an IMU. HOWEVER, control points can be very important to keep IMU measurements within a specified tolerance – especially within gas lines.

  40. GPS BASICS • The global positioning system consists of at least 24 orbiting satellites and 5 ground stations • The Global Positioning System was originally operated by the U.S. Department of Defense primarily for defense applications (that is evolving) • The Russians have a comparable system that is often used elsewhere in the world (GLONASS)

  41. GPS BASICS • Generally, 4 satellites are needed for a GPS location (x,y,z,t) • Code phase tracking is used for navigation • “Pseudo range navigation” samples using the intersection of spheres • Carrier phase tracking is used in surveying - requires baseline and long acquisition intervals

  42. GPS BASICS • Common errors, uncertainties and mistakes: • Frequency noise • Snell’s Law • Atmosphere (troposphere) • Atmosphere (ionosphere) • Tidal effects • Multipath (“scatter”, “splash”)

  43. DIFFERENTIAL GPS AND REFERENCE FRAMES • DGPS can give subcentimeter accuracy - this should not be confused with absolute accuracy • Tectonic shifts and other factors can lead to the absolute position of the tracking stations to be known incompletely • The concept of “where everything is” refers to an Epoch of the reference frame

  44. SOME BASIC GUIDELINES • Anyone running a GPS device for commercial applications should have training in datums/geoids (and projections if projected information is to be reported) • Never accept GPS coordinates without associated metadata • Be careful of error reporting - not all statistical reporting methods are equal! • Cadastral mapping and GPS measurements are not equivalent!

  45. DATA USAGE • Getting all of the potential mapping sources to “work together” correctly requires a basic understanding of reference ellipsoids, datums/geoid, GPS and differences between ellipsoid height and orthometric height. • Metadata is absolutely critical to give appropriate weight to various sources. • The year 2022!

  46. Example:

  47. Example Continued:

  48. Q&A From Presentation • Q: Is all spatial data “unreliable”? (Do I even have a fighting chance on meeting regulatory requirements?) A: Nearly all spatial data has some level of reliability, and all spatial data can be captured, manipulated or stored in a way that can compromise its reliability. There are two answers: 1) tight control over how data is acquired, manipulated and stored; 2) Metadata (including datum/Epoch, transformation processes, etc.) Keep in mind that the center of the Earth is known with 1 centimeter, so it is possible to have very accurate measurements.

  49. Q&A From Presentation • Q: How do I control data along a pipeline segment in an HCA? A: Slides 47 and 48 illustrate a large part of the problem. Knowing the location of pipeline “inflection points” (centers of bends- whether horizontal or vertical) is extremely critical. Geographic coordinates are calculated against the reference ellipsoid using a datum/Epoch. Footage locations are linear. (next slide)

More Related