Title:
2000 Digital 2’ Contours and Digital Terrain Model, Washington County, Minnesota
Originator:
Washington County Department of Transportation & Physical Development, Survey and Land Management Division
Unique Identifier:
5178
Abstract:
This data set contains 2-foot contours, digital terrain model data, and basic planimetric features covering Washington County, Minnesota. The coverage extends a minimum distance of 400 feet outside the county’s boundary in areas where the county boundary is not determined by the St. Croix River or the Mississippi River. Aerial photography, at a scale of 1” = 833’, was gathered at 5000 feet during 3 separate flights during the month of April, 2000 to support the creation of this data set. The data is provided in Public Land Survey System section tiles that edge-match with neighboring tiles. The data is available on CD-ROM in AutoCAD drawing file format or Arc/Info coverage format, (contour and spot elevation data only). All data is in Washington County Coordinate System NAD83 coordinates. Complete project specifications are available for review.
The data set was compiled over an 18 month period of time and was delivered by the contractor to Washington County in increments. The data was subjected to quality control procedures by the county and when the determination was made that project standards had been satisfied the data was made available for distribution.
Purpose:
Uses of the digital 2 foot contours, digital terrain model data, and basic planimetric features within Washington County include: creation of preliminary grading plans, hydrologic analysis, land use planning, zoning enforcement, law enforcement applications, surface water analysis, flood plain management, road design, and the updating of GIS parcel base mapping.
Time Period of Content Date:
April, 2000
The dates of the original aerial photography were:
April 6, 2000 (North 1/3 of Washington County)
April 20, 2000 (East 1/2 of South 2/3 of Washington County)
April 21, 2000 (West 1/2 of South 2/3 of Washington County)
Progress:
Complete
Maintenance and Update Frequency:
Unknown. Washington County may obtain new aerial photography in 2004 or 2005 and use them to update this data set in areas where significant grading or development has taken place.
Spatial extent of data:
All of Washington County, including a buffer that extends a minimum distance of 400 feet outside the county’s boundary in areas where the county boundary is not determined by the St. Croix River or the Mississippi River
Theme keywords:
contours, topography, DTM, digital terrain model, planimetric, elevation
Access Constraints:
Subject to license agreement with Washington County. Contact the Washington County Survey and Land Management Division for data pricing schedule.
Use Constraints:
Subject to license agreement with Washington County.
Contact:
John Baer, Survey Project Coordinator
Washington County Survey and Land Management Division
14949 62nd Street North
P.O. Box 6
Stillwater, MN 55082
Phone: 651-430-6883
FAX: 651-430-6888
E-mail: john.baer@co.washington.mn.us
Browse Graphic:
None
Associated Data Sets:
2000 Digital Orthophotos, Washington County, Minnesota
Attribute Accuracy:
The only attributes with a numeric value of significance to the data set are those attributes containing elevation values. Please see “Vertical Positional Accuracy” below.
Logical consistency:
All polyline features, (AutoCAD), and all arc features, (Arc/Info), are clipped at the section tile boundary and edge-match with corresponding features on adjoining section tiles.
Completeness:
36 PLSS sections located in Township 32 North, Range 21 West, Forest Lake, MN
36 PLSS sections located in Township 32 North, Range 20 West, New Scandia Township, MN
6 PLSS sections located in Township 32 North, Range 19 West, New Scandia Township, MN
36 PLSS sections located in Township 31 North, Range 21 West, Hugo, MN
36 PLSS sections located in Township 31 North, Range 20 West, Marine on St. Croix and May Township, MN
10 PLSS sections located in Township 31 North, Range 19 West, Marine on St. Croix and May Township, MN
36 PLSS sections located in Township 30 North, Range 21 West, Mahtomedi, Dellwood, Willernie and Grant, MN
29 PLSS sections located in Township 30 North, Range 20 West, City of Stillwater, Stillwater Township and Oak Park Heights, MN
36 PLSS sections located in Township 29 North, Range 21 West, Lake Elmo and Oakdale, MN
31 PLSS sections located in Township 29 North, Range 20 West, Bayport, Oak Park Heights, Baytown, Lakeland, Baytown Township, and West Lakeland Township, MN
30 PLSS sections located in Township 28 North, Range 20 West, Afton, Lakeland Shores, Lake St. Croix Beach, and St. Mary’s Point, MN
36 PLSS sections located in Township 28 North, Range 21 West, Woodbury, MN
4 PLSS sections located in Township 28 North, Range 22 West, Newport, MN
28 PLSS sections located in Township 27 North, Range 20 West, Denmark Township, MN
36 PLSS sections located in Township 27 North, Range 21 West, Cottage Grove, MN
12 PLSS sections located in Township 27 North, Range 22 West, St. Paul Park & Grey Cloud Island Twp., MN
6 PLSS sections located in Township 26 North, Range 20 West, Denmark Township, MN
7 PLSS sections located in Township 26 North, Range 21 West, Cottage Grove and Denmark Township, MN
2 PLSS sections located in Township 26 North, Range 22 West, Cottage Grove, MN
Horizontal Positional Accuracy:
795 identifiable features, selected at random from the planimetric objects within the data set, were compared with RTK GPS field measurements of the same points. Using the National Standard for Spatial Data Accuracy, the data set tested as follows:
1.5 feet horizontal accuracy at 95% confidence level for the X coordinate value.
1.5 feet horizontal accuracy at 95% confidence level for the Y coordinate value.
Vertical Positional Accuracy:
865 spot elevations, on a hard surface and selected at random from the data set, were compared with RTK GPS field measurements of the same points. Using the National Standard for Spatial Data Accuracy, the data set tested as follows:
1.2 feet vertical accuracy at 95% confidence level for the Z coordinate value.
Lineage:
This data set was developed under a contract with GRW Aerial Surveys, Inc., Lexington, Kentucky.
Limited planimetric features with 2-foot contours and digital terrain model for Washington County, MN were developed under contract with GRW Aerial Surveys, Inc.
The contractor acquired new, vertical black and white aerial photography at a photo scale of 1”=833’ (1:9996 scale or at an altitude of 5,000 ft.). There were 35 flight lines, 1211 exposures, 1101 exposures used for aerotriangulation (AT), 60% forward overlap and 30% sidelap flown in a north/south direction along PLS section centerlines utilizing a CCNS-4 flight management system. Lines 1 thru 17 were flown on 4-6-00, Lines 19 and 26 thru 35 were flown on 4-21-00, Lines 18 and 20 thru 25 were flown on 4-22-00. The contractor flew the project utilizing a twin engine Cessna T310R turbo-charged aircraft and a Zeiss 15/23 TOP Camera with forward motion compensation and gyro-stabilized mount.
The contractor acquired airborne GPS data using two Trimble 4000SSI ground base units and one Trimble 4000SSI unit located in the aircraft during the photo acquisition flight. Final airborne GPS data was processed using Fly-Kin software. The airborne photo center coordinate data was used as input to the AT solution.
The contractor scanned each film diapositive at a scan resolution of 12 microns to yield a .39’ ground resolution pixel size. During the orthophoto rectification process the pixels were resampled to a ground resolution of .5’. TIFF images were exported for use in the softcopy workstation during data collection process and digital orthophoto production.
A Fully Analytical Aerotriangulation Solution for the entire photo block was developed for use during the data collection and orthophoto production phases. Each diapositive was pugged using a PUG-4 point transfer instrument and then each pug was accurately measured using an Intergraph IMA Stereoplotter. This process connects photo to photo along the flight line with pugs called pass points and connects photos to photos from flight line to adjacent flight line with pugs called tie points. Once the measuring of each pug was completed, a software analysis determined in a local coordinate system of microns how well everything fit. Ground Control and Airborne GPS data was then introduced and a transformation from local system of microns to ground units of feet took place. This then allowed the control network to extend across multiple photos, verified the ground control network and provided independent data of the project ground check points for verification. The final AT solution used for the mapping of this project was produced utilizing Bingo Software. As an independent quality control measure the contractor also produced an AT solution utilizing Albany Software, compared the results and found them consistent.
The results of GRW’s AT solution for 443 identifiable ground target points were compared with coordinate positions determined by county survey personnel using Trimble real time kinematic, (RTK), GPS. Each target was occupied twice with RTK GPS and an X, Y, & Z coordinate was recorded. With the exception of 4 points, the difference between the X, Y, & Z values of the computed AT coordinate value and RTK GPS value was less than 1 foot.
The average of the differences in X, Y, & Z values between computed AT coordinate value and RTK GPS value, taking into account positive and negative signs are listed below:
X = -0.007 feet
Y = -0.004 feet
Z = 0.001 feet
The root mean square error, (RMSE), of the final block adjustment is listed below:
X = 0.304 feet
Y = 0.307 feet
Z = 0.161 feet
The contractor used a combination of analytical (IMA’s, DSR-14’s interfaced with KORK Digital Mapping Software) and softcopy stereoplotters (ZI SSK’s interfaced with Microstation) to collect the mapping data. Planimetric and topographic data was delivered to an extent of 400’ beyond the county boundary.
Planimetric data delivered in AutoCad version 14 was: Road Edges (Urban and Rural), Paved Trails, Railroad Centerlines, Bridges, Major Culverts, Dam Structures, Rivers and Streams, Lakes and Ponds, Towers (Water, Communication, Steel Electrical).
A digital terrain model, (DTM), was created using break lines along changes in slopes and a mass point grid of 50’ for areas requiring contours. The DTM and 2 ’ contours were delivered in AutoCad version 14 dwg format. The 2’ contours were also delivered in Arc/Info format.
Digital elevation model, (DEM), data was created using break lines along major changes in slopes and a mass point grid of 50’for use in developing the orthophotos in areas not requiring contours.
Source Scale Denominator:
1 : 9,996
Entity and Attribute Overview:
The contour and spot elevation data exists in two software formats, AutoCAD and Arc/Info. Planimetric data and Digital Terrain Model data, (DTM), is available in AutoCAD format only.
The Arc/Info coverages are contained in directories unique to each section tile. These directories are named with the letter “w” followed by 7 characters representing the Public Land Survey System section, township and range. Each section tile has two Arc/Info coverages associated with it. An arc, (line), coverage called “TOPO” represents contours with attached attribute data. A point coverage called “SPOT” contains point locations with attached elevation attribute data.
Each section tile has 3 AutoCAD drawing files associated with it. The first drawing file contains contour and spot elevation data. Contours are depicted by unbroken polylines annotated with elevation text on all 10-foot contour intervals. Spot elevations are represented by point entities labeled with the point’s elevation. The second drawing file contains Digital Terrain Model, (DTM), data. This data includes both “hard” and “soft” breaklines represented by polylines. Mass points on a 50’ grid are also shown. The third drawing file contains basic planimetric features located from aerial photography. This data includes hydrologic features, transportation features, major culverts, and additional miscellaneous features. (see layer lists below).
The file naming convention indicates the section tile and type of data contained in the drawing. The first 7 characters of the drawing name represents the Public Land Survey System section, township, and range followed by one of the following 3 letters:
“c” indicates that the drawing file contains contour-related data.
“d” indicates that the drawing file contains DTM data.
“p” indicates that the drawing file contains planimetric data.
Entity and Attribute Detailed Citation:
The two Arc/Info coverages and their associated attribute item names and values are listed below:
Coverage Name:
TOPO
Feature Type:
Arc
Contact Person Information:
John Baer
Washington County Survey and Land Management Division
14949 62nd Street North
P.O. Box 6
Stillwater, MN 55082
Phone: 651-430-6883
FAX: 651-430-6888
E-mail: john.baer@co.washington.mn.us
Distributor:
Washington County Survey and Land Management Division.
Distributor’s Data Set Identifier:
Wash_contours2000.
Distribution Liability:
See Washington County License Agreement.
Transfer Format Name:
AutoCAD Rel. 14 drawing format.
Arc/Info 8.X coverages.
Transfer Size:
AutoCAD format:
Contour & spot elevation data: approx. 1 Mb per section tile.
DTM data:
approx. 1.5 Mb per section tile.
Planimetric data:
approx. 0.25 Mb per section tile
Arc/Info format:
Contour & spot elevation data: approx. 0.7 Mb per section tile.
Ordering Instructions:
Contact: Washington County Survey and Land Management Division
(651) 430-6875
Online Linkage:
none available
