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Vince Hamilton
GIS-T 2008 CAD/GIS Integration in Transportation ProjectsPresented By: Vince Hamilton
Vince Hamilton
You send your spouse to buy an oil pump…
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Quick Overview• Why are they different?• What you have to know to line them up• How to determine your coordinate system• What are Projection Files?• What are World Files?• Surface to Grid Transformation• Finding your combined scale factor • How to line up a CAD file in GIS• How to line up a GIS file in CAD
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Why are they different?
The world is not flat and it not exactly round either. There are different definitions of the curvature of the earth based on where you are. The curvature at the equator is much different than it is at the north or south poles. When an engineering project is surveyed, the surveyors create an accurate description of a small area and tie it to an established curvature definition that is the most accurate for their locale.
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Looking at the “iods”
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What do you have to know to line up your files?
• First you must know the projection, datum and scale factor of the file to be matched.
• Second you must know the projection, datum, and scale factor of the file your are matching.
That’s all you need!
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Learn your coordinate systems
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Latitude and LongitudeDegrees, Minutes, and Seconds
31° 52’ 01”
Decimal Degrees
31.8706
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What is a Projection filePROJCS["NAD_1983_StatePlane_Texas_South_Central_FIPS_4204_Feet",GEOGCS["GCS_North_American_1983",DATUM["D_North_American_1983",SPHEROID["GRS_1980",6378137.0,298.257222101]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]],PROJECTION["Lambert_Conformal_Conic"],PARAMETER["False_Easting",1968500.0],PARAMETER["False_Northing",13123333.33333333],PARAMETER["Central_Meridian",-99.0],PARAMETER["Standard_Parallel_1",28.38333333333333],PARAMETER["Standard_Parallel_2",30.28333333333333],PARAMETER["Latitude_Of_Origin",27.83333333333333],UNIT["Foot_US",0.3048006096012192]]
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Check the Metadata• Spatial_Reference_Information:
– Horizontal_Coordinate_System_Definition:• Planar:
– Map_Projection:» Map_Projection_Name: Lambert Conformal Conic » Lambert_Conformal_Conic:» Standard_Parallel: 28.383333 » Standard_Parallel: 30.283333 » Longitude_of_Central_Meridian: -99.000000 » Latitude_of_Projection_Origin: 27.833333 » False_Easting: 1968500.000000 » False_Northing: 13123333.333333
• Planar_Coordinate_Information:– Planar_Coordinate_Encoding_Method: coordinate pair – Coordinate_Representation:
» Abscissa_Resolution: 0.001024 » Ordinate_Resolution: 0.001024
– Planar_Distance_Units: survey feet – Geodetic_Model:
• Horizontal_Datum_Name: North American Datum of 1983 • Ellipsoid_Name: Geodetic Reference System 80 • Semi-major_Axis: 6378137.000000 • Denominator_of_Flattening_Ratio: 298.257222
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Images use World Files1.000000000000000.000000000000000.00000000000000-1.000000000000003120402.6990220001900013845141.00324700028000
Line 1: (A) X scale in resulting X directionLine 2: (B) Y scale in resulting X directionLine 3: (C) X scale in resulting Y directionLine 4: (D) Y scale in resulting Y directionLine 5: (E) X coordinate of the center of the center of rotation(the center of the Upper Left Pixel of the unrotated image)Line 6: (F) Y coordinate of the center of the center of rotation(the center of the Upper Left Pixel of the unrotated image)
or in algebraic form
X' = (A*X) + (B*Y) + E Y' = (C*X) + (D*Y) + F
where X’ and Y’ are georeferenced coordinates and x is pixel columns and y is pixels rows
D is negative because pixel rows increase opposite an increasing northing direction. B and C are zero for unrotated and unsheared georeferences A and D are zero for 90 and 270 degree rotations world file ax + by center for more references
The file extensions can be *.tfw,ttw,wld
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How projections are handled in GIS
When you create a map in ESRI you must define the map projection. The ESRI software uses the projection files to “project” the data to match your map “on the fly”. If the map is in NAD83 and you attach a data set that is in NAD27, the software will automatically “re-project” the data to NAD83 without writing it out to a new file.
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CAD files have projections tooWhen a CAD file is added to GIS using the CAD feature class in white,a projection will be applied if a .prj file exists with the same name as the CAD file.The CAD symbology will also be applied to the GIS layer. The .prj files are being phased out and replaced with XML files that contain the Metadata for each file.
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One for ALL and ALL for One
If all of the CADD files in the same folder have the same projection, then you can use a single projection file. Create the projection file and then rename it to ESRI_CAD.prj. The GIS software will use this projection for all of the CADD files in that folder.
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Use ArcCatalog to define or create a projection
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Selecting an existing projection
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Texas State Mapping System Shakleford Projection
System Name Texas State Mapping System (Shakleford)
Projection Lambert Conformal ConicSpheriod GRS80Datum NAD83Central Meridian -100Reference Latitude 31.16667Standard Parallel 1 27.41667Standard Parallel 2 34.91667False Easting (Meters) 1000000False Northing (Meters) 1000000Units Meters
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Texas Centric Mapping System
System NameTexas Centric Mapping
System/Lambert Conformal(TCMS/LC)
Texas Centric Mapping System/Albers Equal
Area(TCMS/AEA)Projection Lambert Conformal Conic Albers Equal Area ConicSpheriod GRS80 GRS80Datum NAD83 NAD83Central Meridian -100 -100Reference Latitude 18 18Standard Parallel 1 27.5 27.5Standard Parallel 2 35 35False Easting (Meters) 1500000 1500000False Northing (Meters) 5000000 6000000Units Meters Meters
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Create each Texas Coordinate SystemYou can simply copy the resulting .prj file to the same name as the CAD file and the GIS software will use it. For example the CAD file BW8E.DGN would have a corresponding BW8E.PRJ file.
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The coordinate systems are right but they still don’t line up
This is due to the fact that engineering surveys use ground surface coordinates and GIS uses the projection grid.
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Don’t make that move!You cannot simply move a CAD file from surface to grid
coordinates, it must be scaled. It must be scaled from 0,0 so that the combined scale factor is applied across the entire projected grid. The TxDOT district 12 standard scale factor is 1.00013. This does not seem like a very large number, but the Texas NAD 83 coordinates in the Houston area are in the neighborhood of 7,000,000 in the X and 13,000,000 in the Y. That is roughly 90 feet in the X and 1,690 in the Y direction. Note that this conversion is from grid to surface, we want to go the other way so you use the reciprocal value of .99987 to scale an engineering CAD file down to the GIS grid coordinates.
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CAD file without surface to grid scale factor applied
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CAD file in GIS after applying the surface to grid scale factor
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Where do I get the Scale Factor?
The engineering plan sets will have the scale factor on either the title sheet, the general notes sheet or the geometric layout sheet.
TxDOT has assigned scale factors for each county and that information is on the following pages.
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Zone 4201 North ZoneCounty Surface Adjustment FactorArmstrong 1.00019Brisco 1.00009Carson 1.00019Castro 1.00013Childress 1.00009Collinsworth 1.00019Dallam 1.00013Deaf Smith 1.00019Donlev 1.00019Grav 1.00019Hall 1.00009Hansford 1.00013Hartley 1.00019Hemphill 1.00019Hutchison 1.00019Lipscomb 1.00013Moore 1.00019Ochiltree 1.00013Oldham 1.00019Parmer 1.00013Potter 1.00019Randall 1.00019Roberts 1.00019Sherman 1.00013Swisher 1.00013Wheeler 1.00019
Vince HamiltonZone 4202 North Central ZoneCounty Surface Adjustment FactorAndrews 1.00021Archer 1.00012Bailey 1.00012Baylor 1.00012Borden 1.00021Bowie 1.00012Callahan 1.00012Camp 1.00012Cass 1.00012Clay 1.00006Cochran 1.00021Collin 1.00012Cooke 1.00012Cottle 1.00006Crosby 1.00021Dallas 1.00012Dawson 1.00021Delta 1.00012Denton 1.00012Dickens 1.00021Eastland 1.00012Ellis 1.00006Erath 1.00006Fannin 1.00012Fisher 1.00021Floyd 1.00009Foard 1.00006Franklin 1.00012Gaines 1.00021Garza 1.00021Grayson 1.00012Gregg 1.00012Hale 1.00012Hardeman 0.99994Harrison 1.00012Haskall 1.00012Henderson 1.00006Hill 0.999976Hockley 1.00021
County Surface Adjustment FactorHood 1.00012Hopkins 1.00012Howard 1.00012Hunt 1.00012Jack 1.00012Johnson 1.00012Jones 1.00012Kaufman 1.00012Kent 1.00021King 1.00012Knox 1.00012Lamar 1.00012Lamb 1.00012Lubbock 1.00011Lynn 1.00021Marion 1.00012Martin 1.00021Mitchell 1.00012Montague 1.00012Morrls 1.00012Motley 1.00008Navarro 0.999976Nolan 1.00012Palo Pinto 1.00012Panola 1.00006Parker 1.00012Rains 1.00012Red River 1.00012Rockwall 1.00012Rusk 0.999976Scurry 1.00021Shackleford 1.00012Smith 1.00012Somervell 1.00006Stephens 1.00012Stonewall 1.00021Tarrant 1.00012Taylor 1.00012Terry 1.00021
County Surface Adjustment FactorThrockmorton 1.00012Titus 1.00012Upshur 1.00012Van Zandt 1.00012Wichita 1.00006Wilbarger 0.999976Wise 1.00012Wood 1.00012Yoakum 1.00021Young 1.00012
Vince HamiltonZone 4203 Central ZoneCounty Surface Adjustment FactorAnderson 1.00003Angelina 1.00012Bastrop 1.00003Bell 1.00012Blanco 1.0001Bosque 1.00003Brazos 1.00012Brown 1.0001Burleson 1.00012Burnet 1.00012Cherokee 1.00003Coke 1.00012Coleman 1.0001Comanche 1.00003Concho 1.0002Coryell 1.00012Crane 1.0002Crockett 1.0002Culberson 1.00025Ector 1.00012EI Paso 1.000181733Falls 1.00011Freestone 1.00003Gillespie 1.00012Glasscock 1.00012Grimes 1.00012Hamilton 1.00001Hardin 1.00003Houston 1.00012Hudspeth 1.00025Irion 1.0002Jasper 1.00012Jeff Davis 1.0002Kimble 1.00012Lampasas 1.00012Lee 1.00003Leon 1.00012Liberty 1.00003Limestone 1.00012
County Surface Adjustment FactorLlano 1.00012Loving 1.00012Madison 1.00012Mason 1.00012McCulloch 1.00012McLennan 1.00012Menard 1.0002Midland 1.00012Milam 1.00012Millis 1.00012Montgomery 1.00003Nacogdoche 1.00012Newton 1.00012Orange 1.00003Pecos 1.0002Polk 1.00012Reagan 1.0002Reeves 1.0002Robertson 1.00012Runnels 1.00012Sabine 1.00012San Augusti 1.00012San Jacinto 1.00012San Saba 1.00012Schleicher 1.0002Shelby 1.00003Sterling 1.00012Sutton 1.00012Tom Green 1.0002Travis 1.0001Trinity 1.00012Tyler 1.00012Upton 1.0002Walker 1.00012Ward 1.0002Washington 1.00003Williamson 1.00012Winkler 1.00012
Vince HamiltonZone 4204 South Central ZoneCounty Surface Adjustment FactorAransas 0.999894Atascosa 1.00013Austin 1.00013Bandera 1.00013Bee 1Bexar 1.00013Brazoria 1.00013Brewster 1.0002Caldwell 1.00013Calhoun 1Chambers 1.00013Colorado 1.00013Comal 1.00013DeWitt 1.00013Dlmmit 1Edwards 1.00013Fayette 1.00013Fort Bend 1.00013Frio 1.00013Galveston 1.00013Gollad 1.00007Gonzales 1.00013Guadalupe 1.00013Harris 1.00013Hays 1.00013Jackson 1.00013Jefferson 1.00007Karnes 1.00013Kendall 1.00013Kerr 1.00013Kinney 1.00013La Salle 1Lavaca 1.00013Live Oak 1Matagorda 1.00013Maverick 1.00007McMullen 1Medina 1.00013Presidio 1.00002
County Surface Adjustment FactorReal 1.00013Refugio 1Terrell 1.00013Uvalde 1.00013Val Verde 1.00013Victoria 1.00013Waller 1.00013Wharton 1.00013Wilson 1.00013Zavala 1.00013
Vince HamiltonZone 4205 South Zone
County Surface Adjustment FactorBrooks 1.00004Cameron 0.99996Duval 1.00004Hidalgo 1.00004Jim Hogg 1.00004Jim Wells 1.00004Kenedy 1.00004Kleberg 1.00004Nueces 1.00004San Patricio 0.99996Starr 1.00004Webb 1.00003Willacy 1.00004Zapata 1.00004
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Scale Factors can be refined down to the minute of Latitude
The next few pages have the scale factors for the Texas South Central Zone for each change of minute of Latitude.
Vince HamiltonSurface Scale FactorsFor Texas South CentralZone 4204
Vince HamiltonSurface Scale FactorsFor Texas South CentralZone 4204
Vince HamiltonSurface Scale FactorsFor Texas South CentralZone 4204
Vince HamiltonSurface Scale FactorsFor Texas South CentralZone 4204
Vince HamiltonSurface Scale FactorsFor Texas South CentralZone 4204
Vince HamiltonSurface Scale FactorsFor Texas South CentralZone 4204
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Units of measure (Linear) Rectangular coordinate systems may use meters, international foot, or the U.S. Survey Foot as
the unit of measurement. (Most surveying and mapping work at the local level is based on the U.S. Survey Foot.) When a conversion from one of these units to the other is performed, it is important to ascertain which standard foot (U.S. Survey or international) is involved. .
The international (S.I.) foot, based upon a redefinition of the meter in 1959, is equivalent to 0.3048 meter.
The U.S. Survey Foot, upon which many years of land tenure information and legislation are based, retained the 1893 definition of 1200/3937 meter*.
* For conversion of meters to U.S. Survey Foot, multiply the meters by 3.28083333333 (to 12 significant figures).
For conversion of meters to international feet, multiply the meters by 3.28083989501 (to 12 significant figures).
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What definition of a foot should we be using?
Although the international foot is the latest definition (1959), survey feet is still the predominate unit because of the implications with legacy surveys and deed descriptions.
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Does it really matter?
• Short distances < 1000 feet– US Survey Foot = International Foot (measured 1/100
of a foot)• At 100,000 feet
– Definitions result in a difference of about .2 feet• At 1,000,000 feet
– Definitions result in a difference of about 2 feet• At 10,000,000 feet
– Definitions result in a difference of about 20 feet
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Edit the units.def file in MicrostationComment out the ft definition using the # in the International FootAnd remove the # from the sf,ft definition in the US Survey Foot section.
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Using aerials in Microstation
In most cases the latest aerial photography is created for planning and GIS use. The images are typically in GRID coordinate systems and in many cases in a different mapping projection. The aerials are normally clipped by a defined grid such as the Lambert grid in this case. This is used ti identify what aerials you need for your project.
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Step by Step• In Microstation, add the aerial using the
coincident world option. The image should have a world file that puts it in the right location.
• Check the coordinates to make sure it is in the correct projection, it will not match up exactly at this time so don’t worry. If the coordinates are off by over a million you have a difference in datums and will need to project a CAD version of the grid to the correct datum and use the interactive method to attach the aerials using the grid corners.
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Native aerials in Microstation
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Save As HMR3. In this case the aerials are in Mr. SID
format and they are cumbersome to use. Export the aerials to .HMR for faster display times.
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Attach as reference to project
5. After the aerials have been attached and converted to HMR, exit the aerial file and open the roadway in Microstation.
6. Attach the aerial file as a reference file.
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Before Scaling Reference File
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Apply the surface to grid scale factor by scaling the reference file
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After Scaling the reference file
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One file, many references
One distinct advantage to this method is that the aerial DGN file can be referenced to different projects that might be using a different scale factor. Because the aerials are in their native position, you just need to attach it as a reference and use the correct scale factor.
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Magnetic Declination (NOAA)http://www.ngdc.noaa.gov/seg/geomag/jsp/struts/calcIGRFWMM
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