Evaluation of TXDOTs Digital Base Map - PowerPoint PPT Presentation

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Evaluation of TXDOTs Digital Base Map

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... for printed maps is 1/30th ... Compare Digital maps against more accurate standard ... Actual road data compared to same road segments of digital maps ... – PowerPoint PPT presentation

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Title: Evaluation of TXDOTs Digital Base Map


1
Evaluation of TXDOTs Digital Base Map
  • By
  • Michael Flaming

2
Digital Map Standards
  • National Map Accuracy Standard
  • 90 of tested points smaller that threshold
  • 124,000 threshold for printed maps is 1/30th of
    an inch 66.66 feet
  • No national standard for digital maps
  • some claim to conform to NMAS

3
Aerial Photo Metadata
  • Map Name  CAPCO 2002 Orthophotography Project
    Imagery
  • Photo Scale           13000'
  • Horizontal Datum      NAD83
  • Coordinate system     US State Plane
  • State Plane Zone      Texas Central
  • State Plane FIPSZone  4203
  • Projection            Lambert Conformal Conic
  • Photo Flight Date     February 2002
  • Camera Name           RC30 5236
  • Film Type             Kodak Aerocolor III 2444
  • Focal Length          153.026mm
  • Aircraft Height (AMT) 18000'
  • Horiz. Accuracy Std.   /- 4'
  • Bounding Box in US State Plane Zone 4203
  •    Upper Left   3231310, 10022634
  •    Upper Right  3241957, 10022634
  •    Lower Left   3231310, 10010542
  •    Lower Right  3241957, 10010542
  • Description  Color Aerial Photography captured
    for the

4
Evaluate Horizontal Accuracy
  • Compare Digital maps against more accurate
    standard
  • Accuracy of digital maps on the order of 5-10m
  • Accuracy of differentially corrected GPS on the
    order of

5
Analysis of Accuracy
  • Test routes selected
  • Urban Interstate Highway (I-35)
  • Urban State Highway (US 183, Mopac)
  • Rural State Highway (US 183 Lockhart)
  • Loop 360, 2222, FM163
  • High accuracy GPS data collected
  • Actual road data compared to same road segments
    of digital maps
  • Various buffers used to compute map coverage
    ratio
  • Buffer represents range in which results are
    accurate
  • For a given coverage ratio, the larger the buffer
    the lower the accuracy
  • For a given buffer, the greater the coverage
    ratio, the higher the accuracy

6
GPS Data Collection
Trimble Pro XRS Receiver
Trimble Recon Data Collector
1989 Nissan Maxima w/sunroof
7
GPS Data
I 35
LP 360
US183
8
TXDOT Base Map
9
GPS Data
Focus area LP360
10
GPS (Maxima) Line
11
TXDOT Base map Line
12
Calculate buffer
13
10m buffer of GPS line
14
Calculate Intersect
15
Intersect of 10m buffer of GPS line and TXDOT
Basemap
16
3m buffer of GPS line
17
Intersect of 3m buffer
18
Attributes of Intersect
  • Same as attributes of base map
  • Shape length in decimal degrees
  • Original Projected line length in meters
  • Must calculate new shape lengths

19
VBA Script to Calculate Length
  • Gathers up all the bits of lines and adds up
    the sum
  • Separated by object ID

20
New Line length
  • Field calculation to get new line length

21
Resulting data for LP 360
  • Nine attribute tables for each buffer intersect
    dumped to Excel for analysis

22
Attribute table
23
Omitted data
  • Portions that were obviously outdated due to
    recent construction were omitted.

24
LP 360 Graph
25
Coverage Ratio
26
Conclusions
  • Linear features of TXDOT roadbed basemap have an
    accuracy of /- 7m with a confidence of 90.

27
Questions?
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