What’s Your Angle? What’s Your Angle? Slope Modeling & Terrain AnalysisSlope Modeling & Terrain AnalysisJessica Gormont & Rachel ShirleyJessica Gormont & Rachel Shirley

33rdrd Eastern Panhandle, West Virginia GIS Users Group Meeting Eastern Panhandle, West Virginia GIS Users Group Meeting

September 18, 2009September 18, 2009

INTRODUCTIONSINTRODUCTIONS

• Jessica Gormont GIS Technician, Jefferson County

• Rachel Shirley GIS Intern, Jefferson County

• Project Members:– Todd Fagan GIS Specialist, Jefferson County

– Jennie Brockman Planning & Zoning Director, Jefferson County

– Dr. Edward Snyder Professor, Shepherd University

– John Maxey Jefferson County Planning Commission

LINEUP LINEUP

• Background• Purpose• Definitions• Field QA• Data• Results• Future Applications

BACKGROUNDBACKGROUND

Project Culmination:

• Planning concerns in the Blue Ridge Mountain Community

• GIS Office tasked by County Commission to fill data gaps – slope, 2 ft contours, land cover

• Will aid planning staff and public analyze topography

PURPOSEPURPOSE

• Purpose: To create an accurate slope model for the entire County, focusing on the Blue Ridge Mountain Area

• Slope 2ft topographic contours, land cover

BLUE RIDGE MOUNTAIN STUDY AREABLUE RIDGE MOUNTAIN STUDY AREA• “The Mountain”: all land in

Jefferson County east of the Shenandoah River

• Area = 24.3 sq mi (11% of County)

• Elevation = Approx. 250ft to 1700ft (1450ft change)

• Includes Federal, State, County, and privately owned land

• Addresses = 3,285 (13% of County) mostly residential

WHY USE GIS FOR STUDY?WHY USE GIS FOR STUDY?

• Can generate slope over large areas quickly

• Less chance for human error

• Combine with other overlays for enhanced understanding of land conditions

DEFINITIONS - SLOPEDEFINITIONS - SLOPE

Measured in Percent or Degrees

50% = 26.5° 100% = 45° 150% = 56.3° Infinite = 90°

Photo Source: LaserCraft Inc.

Slope is “an inclined surface or ground that has a natural incline”.

DEFINITIONS - LIDARDEFINITIONS - LIDAR

Photo Source: Dewberry

LiDAR (Light Detection And Ranging) is an optical remote sensing technology that utilizes light to gather topographic data.

DEM Hillshade

METHODS/DATAMETHODS/DATA

5 methods compared:

• Field calculated slope with laser range finder

• 10-meter Slope Model

• 3-meter Slope Model

• 1-meter Slope Model

• Rise/Run using 1-meter DEM and points obtained from GPS

FIELD CALCULATIONSFIELD CALCULATIONS

• 34 locations for field slope verification

• Selection Attributes:– Varying levels of slope

(gentle, moderate, and steep)

– Ownership (public vs. private)

– Distribution over study area

– Un-modified since 2003

FIELD CALCULATIONSFIELD CALCULATIONS

• Equipment:

– Contour XLRic Laser Rangefinder (LaserCraft Inc.)

– Trimble Geo XT handheld GPS receiver

ACCURACYACCURACY

• LaserCraft Contour XLRic Laser Rangefinder:– Range Accuracy = 0.10 meter at 85 meters

– Inclination = +/- 0.1 degrees

• Trimble Geo XT handheld GPS receiver:– Horizontal Accuracy = < 1 meter (submeter)

– Vertical Accuracy = 1.5 to 2 meters

FIELD WORKFIELD WORK

• Measured points: 10ft and 40ft from basepoint

• Slope calculated by internal inclinometer

• Gathered GPS points (at basepoint, 10ft target, and 40ft target) for mapping purposes Blue Ridge

Elementary SchoolField Slope = 22%

DATADATA

• 10-meter Slope Model– 2003 USGS 10-meter DEM (UTM NAD 1983)– Vertical Accuracy = +/- 7 meters

• 3-meter Slope Model– 2003 USGS 3-meter DEM (UTM NAD 1983)– Vertical Accuracy = +/- 1 meter

• 1-meter Slope Model (LiDAR)– 2005 USDA-NRCS 1-meter DEM (UTM NAD 1983)– Vertical Accuracy = 0.15 meter

DATA GENERATEDDATA GENERATED

1) Drew slope lines between points

2) Used Hawth’s Analysis Tools to calculate slope of line for each DEM

3) Plotted model v. field slopes on graph

4) Obtained R2 value for each dataset from linear regression model

10-m NED DEM (USGS)10-m NED DEM (USGS)

3-m NED DEM (USGS)3-m NED DEM (USGS)

1-m LiDAR DEM (USDA-NRCS)1-m LiDAR DEM (USDA-NRCS)

RESOLUTION PROGRESSIONRESOLUTION PROGRESSION

10-m Slope 3-m Slope 1-m Slope

RESULTSRESULTS

• 1-meter LiDAR DEM more accurate than other datasets available:– Higher R2 value– Finer detail allows for more accurate representation of

the surface

FINAL MAPFINAL MAP

• This is the map generated using the best available, most accurate, digital data

Legend

^ Slope Points

0 - 16

16 - 24.99

25 - 40

40 - 60

60 and above

ZOOMING IN…ZOOMING IN…

BLUE RIDGE ELEMENTARY BLUE RIDGE ELEMENTARY SCHOOLSCHOOL

Legend

^ Slope Points

0 - 16

16 - 24.99

25 - 40

40 - 60

60 and above

Field Slope = 22%

Slope Model = 16 – 24%

POTENTIAL FUTURE USESPOTENTIAL FUTURE USES

1. 2-ft topographic contours

2. Useful for baseline data for future comprehensive plans

3. Data freely accessible by citizens for planning purposes

4. If used, would provide monetary savings to the public

5. Better way to measure average slope for an area

6. Useful for determining amount of necessary remediation on a site

7. Sub-watershed and riparian zone delineation

TRUE 3D LINE OF SIGHT ANALYSISTRUE 3D LINE OF SIGHT ANALYSIS

HIGH RESOLUTION LAND COVERHIGH RESOLUTION LAND COVER

Legend

Tree Canopy

Grass/Shrub

Water

Buildings

Roads/Railroad

Other Paved

Legend

Tree Canopy

Grass/Shrub

Water

Buildings

Roads/Railroad

Other Paved

POTENTIAL FUTURE USES CONTD.POTENTIAL FUTURE USES CONTD.

Land Stability Map:

– Would include overlay of soils, geology, land cover, impermeable surfaces, tree canopy, etc

– Could be combined with Universal Soil Loss Equation (USLE) to determine potential soil loss

– Useful for assessing potential ground-movement and erosion-prone areas

SUMMARYSUMMARY

• Most accurate data available

• Reasonably represents the terrain in Jefferson County

• Provides a good confidence of accuracy for 2-ft contours

• 1-m LiDAR can be used for planning purposes and combined with other data layers for the creation of valuable datasets

ACKNOWLEDGEMENTSACKNOWLEDGEMENTS

• Jennie Brockman• John Maxey• Dr. Ed Snyder• Mike Schwartz• John Young• University of

Vermont

REFERENCESREFERENCESAguilar, F. and J. Mills. 2008. Accuracy Assessment of LiDAR-derived digital elevation models. The

Photogrammetric Record 23(122): 148-169.

Beyer, H. L. 2004. Hawth's Analysis Tools for ArcGIS. Available at: http://www.spatialecology.com/htools.

LaserCraft Inc. 2009. Contour XLRic Laser Rangefinder. Norcross, GA.

FEMA 2003. Federal Emergency Management Agency. Guidelines and Specifications for Flood Hazard Mapping Partners, Appendix A: Guidance for Aerial Mapping and Surveying. Available online at http://www.fema.gov/library/viewRecord.do?id=2206.

FGDC 1998. Federal Geographic Data Committee. Geospatial Positioning Accuracy Standards, Part 3: National Standard for Spatial Data Accuracy. FGDC-STD-007.3-1998. Available online at http://www.fgdc.gov/standards/projects/FGDC-standards-projects/accuracy/part3/chapter3.

NDEP 2004. National Digital Elevation Program. Guidelines for Digital Elevation Data, Version 1.0. Available online at http://www.ndep.gov/NDEP_Elevation_Guidelines_Ver1_10May2004.pdf.

Trimble Navigation Limited 2009. Trimble GeoXT Handheld Receiver. Sunnyvale, CA.

USDA-NRCS 2005. United States Department of Agriculture-Natural Resources Conservation Service. 1-m LiDAR Raster Dataset. 07/31/2005.

USGS 2003a. United States Geological Survey. National Elevation Dataset (NED) 1/9 Arc Second (~ 3m resolution). Available at: http://seamless.usgs.gov/products/9arc.php.

USGS 2003b. United States Geological Survey. National Elevation Dataset (NED) 1/3 Arc Second (~10m resolution). Available at: http://seamless.usgs.gov/products/3arc.php.