Projection System Basics Only You Can Prevent Computational Errors. Presented by : Frank Weiss PE, Kema Consulting

Transcription

1 Projection System Basics Only You Can Prevent Computational Errors Presented by : Frank Weiss PE, Kema Consulting

2 Projection System Basics Only You can prevent Computational Errors Outline Background Apparent errors Analysis Projection systems Conclusions

3 Learning Objectives What are projection systems How these can be an issue in merged utilities Not understanding how these are used can cause problems

4 Background Merged data from 3 different GIS s into one Integrated GIS with an Outage Management System Integrated GIS to work management in the new ERP Migrated asset data to the new ERP Migrated CIS data to the new ERP Integrated OMS to ERP for calls and work orders

5 Integration Points ERP - GIS Work Order Created Job Design As Built Posted ERP GIS OMS GIS Circuit Load OMS Mobile

6 Integration Points ERP - GIS Work Order Created Job Design As Built Posted ERP - OMS ERP Receive Outage Calls Return Status Information Work Order Creation Restoration Completion Follow Up Work GIS OMS OMS GIS Circuit Load Mobile OMS - Mobile Send Order Report Status Completion information

7 Conversion Approach The utility converted from three old AM/FM systems to a new GIS between June 1998 and March Electronic data translation (No paper conversion) Effort was performed through a combined effort of in house IT & business personnel, Consultants and Conversion specialists.

8 Distribution Equipment Conversion Facilities New GIS ERP Prop Records MPRS PIPS FCPR XMTR XJTR Export/ Merge Process Prop Records ONLY New GIS ONLY Matches Load File JLTS

9 Conversion Schedule Develop and Test Conversion Software Send/Receive GIS data (translated by vendor) Load GIS data in Production Two Months to Design and develop the Conversion Two weeks Software to send Two weeks to receive Two weeks data to load data For after each receipt area North East West One month to load 7/3/98 9/1/98 7/3/98 9/1/98 7/3/98 9/1/98 pole/ pad data to the ERP One month to load facilities data to the ERP 9/1/98 9/15/98 10/1/98 10/15/98 11/1/98 11/15/98 9/15/98 9/30/98 10/15/98 10/30/98 11/15/98 11/30/98 Load Distribution Functional Locations in Production Load Distribution Equipment in Production 10/1/98 10/30/98 11/1/98 11/30/98 12/1/98 12/30/98 10/1/98 10/30/98 11/1/98 11/30/98 12/1/98 12/30/98

10 Underlying Data Each data source based on a different coordinate system (3 different State Plane systems) Some of the coordinate references had been adjusted Target GIS to use a single UTM coordinate system

11 Underlying Data Western Area Used an internal field audit to initially populate the original IBM GFIS data model. Used a modified state plane coordinate system - USGS.

12 Underlying Data Northern Area Used vendor to scan old maps Used match against the property records systems and the old hierarchical circuit system Used a separate state coordinate system - USGS

13 Underlying Data Eastern Area Used vendor to perform field audit Used state plane coordinate system - USGS

14 The Problem

15 The Problem It appeared that the translation code was in error. The distances between objects were off if you compared State Plane measurements to GIS values When comparing data to that pre-conversion, the data appeared rotated. As a result, some of the data that should be on a map does not appear. The code was incorporated in the GIS, so all new data were also shifted by the same amount.

16 Normal Creation of Map Products

17 Effect of Rotation on Map Products

18 Preliminary Evaluation (X1, Y1) (X2, Y1) (X1, Y2) (X2, Y2) Left Right Delta Calc. Error Top Bottom Delta X1 X2 X X Y1 Y2 Y Y Northern area Top Left Bottom Right Point Error Point Error Western area Top Left Bottom Right Point Error Point Error Eastern area Top Left Bottom Right Point Error Point Error Calc. Error

19 Intermediate Evaluation Y= X *.031 Length = X COS 1.78 X= - Y *.031 A quick sample showed that the x and y coordinates vary by 311 over a 10,000 distance. This can be represented by a shift in the axis around a point of origin as shown here The angle associated with this shift is approximately 1.78

20 Evaluation Over a Large Area Comparison of Errors Associated With Horizontal Segments Area: Eastern Segment Lengths: 100,000 Ft Span Analyzed: 189 mi. X Y X Diff (Should be 100,000) % Error 0.04% 0.03% 0.02% 0.02% 0.01% 0.01% 0.02% 0.02% 0.03% 0.04% Y error* Delta Delta as % of error -0.1% 0.0% -0.1% 0.0% -0.1% 0.0% -0.1% 0.0% -0.1% * Y error is defined as the distance between the previous Y coordinate and the current For a horizontal line, it should be 0.

21 Impact of the error Map product creation Setting boundaries (std products) Setting boundaries (ad hoc maps) Border treatments (tic Marks) External data sources External agencies GPS

22 Options Option 1 Compensate for the Error Option 2 Relocate Geometries Calculation did not appear to be a problem 2 a) Move Geometries 2 b) Delete and Recreate Geometries

23 Option 1 - Compensate for Error Adjust map products for the error in angle Need to be mindful that this error exists whenever importing or displaying information created externally. GPS readings for imported data would have to be adjusted Importing drawings from a developer would require warping of the information This is commonly required, even when there are no data errors.

24 Option 2 Risks (Relocation) Another Data Conversion Effort QA/QC, Clean up, etc Evaluate Triggers and Rules Test, test, test General Connectivity Risk Manage versions Grab only changes Reestablish connectivity Maintain Outage Management System

25 Further Evaluation of the Translation Code Only minor calculation errors were found in the source code. Data translations were then compared to those generated by industry standard routines. It was found that the translation had been done correctly, with minor variances! The culprit was in the way the Program Call was being employed.

26 How the Program Call was Implemented In order to continue to make state plane references to information, the utility had incorporated the program originally developed conversion. This program was called to return state plane coordinates for placing objects, drawing lines and was used in the creation of the map boundaries for existing map products.

27 What Was really Happening The projector program does its calculations in the following order when drawing a line: Convert state plane to lat/long Convert lat/long to utm Add offset to utm Convert UTM to lat/long Convert lat/long to state plane The projector does the offset in the UTM plane and therefore the state plane coordinates appear skewed compared to offsets created entirely within the state plane coordinate systems.

28 Why Does This Occur Projection Systems Involved Lambert conic projection which results in a cone when unfolded Transverse mercator state plane coordinate system UTM system which result in a plane

29 Problems With Squashing a Sphere onto a Plane Look Closer

30 Problems With Squashing a Sphere onto a Plane A B

31 Problems With Squashing a Sphere onto a Plane A B

32 Projecting a Sphere onto a Cone

33 Universal Transverse Mercator (UTM) Projections Created by the U.S.C.G.S.

34 Lambert conic The state plane system with Lambert conic projection results in a cone when unfolded. The unfolded cone is laid on top of the plane. Points can be properly converted between the two systems, but offsets and orientations cannot be maintained when converting between systems.

35 Lambert Conic Projection Squashed Onto a UTM Plane N UTM Plane E P0 DX P1 P2 Conic Projectioin The diagram represents an unfolded cone on top of a plane. It contains three points P0, P1and P2 where P0 is the original point. P1 and P2 are offset points from P0 by some horizontal distance DX. Inspecting the diagram will show that P0 is the same in both systems. N State Point P0 E

36 N UTM Plane E Conic Projectioin DX P1 Lambert Conic P0 P2 N State Point P0 Offsetting a point by distance DX in the horizontal direction in the UTM system will result in a horizontal line with endpoint P1. Offsetting a point by distance DX in the horizontal direction in the conic system will result in a horizontal line in the conic system with end point P2. So if you offset in one system, the other system will seem skewed. The coordinates of P1 using the UTM system will be: E UTM system: Conic system: P0.X+DX, P0.Y P0.X+fx(DX), P0.Y+fy(DX) where fx(dx) and fy(dx) are functions that are dependent on the offset distance.

37 Mercator projection * The Mercator projection has straight meridians and parallels that intersect at right angles. Scale is true at the equator or at two standard parallels equidistant from the equator. The projection is often used for marine navigation because all straight lines on the map are lines of constant azimuth. *

38 Transverse Mercator State Plane N UTM Plane E Diagram 2 State Plane TM N E P 2 P 0 P 1 Dx

39 Transverse Mercator State Plane The same types of consequences happen between UTM plane and a transverse mercator.system. The difference in this case is that the offset DX in the horizontal direction results in an apparent rotation in the opposite direction of the rotation in the Lambert conic projection.

40 Impact Revisited Map product creation Setting boundaries (std products) Setting boundaries (ad hoc maps) Border treatments (tic Marks) External data sources External agencies GPS

41 Other Projection References University of Texas (A good introduction) mapproj & datum POSC (Technical data models and parameters) POSC is an international not-for-profit membership corporation. data model & examples of usage About The Human Internet (A general reference Internet page) (Second line is map projection specific)

42 More References Mercator s World (Many historical references) Virtual Library (UK) (Map History/ History of Cartography)

43 Conclusions Conversion is an expensive effort, take care to do it right. (You do not want to redo it) The decisions you make at conversion will affect you for years. Make sure you understand the consequences of the decisions Once converted, be careful in comparing data to the old system. Just because they are different, doesn t mean one is wrong

44 Projection System Basics Only You can prevent Computational Errors Questions? Frank Weiss P.E.

45 Thank You!