14
303.427.2231 | [email protected] | www.cad-1.com | ©2013 CAD-1, Inc. GIS, CAD, and Coordinate Systems Warren Geissler, ACI Geospatial Specialist
| Date post: | 29-Jun-2015 |
| Category: |
Technology |
| Upload: | gis-in-the-rockies |
| View: | 123 times |
| Download: | 2 times |
303.427.2231 | [email protected] | www.cad-1.com | ©2013 CAD-1, Inc.
GIS, CAD, and
Coordinate Systems
Warren Geissler, ACIGeospatial Specialist
303.427.2231 | [email protected] | www.cad-1.com | ©2013 CAD-1, Inc.
Background: Civil Engineering &
Surveying
10 Years U.S.A.F
CADD Manager in
Colorado
17 Years Instructor and
Support Tech in Autodesk
Channel
Warren Geissler, CAD-1Geospatial Technical Specialist
Training Center Manager
303.427.2231 | [email protected] | www.cad-1.com | ©2013 CAD-1, Inc.
Welcome to CAD
Even though GIS is exposed to CAD frequently, it is important for GIS
professionals to remember that CAS is very broad reaching application.
CAD creates everything from screws
…to cities
303.427.2231 | [email protected] | www.cad-1.com | ©2013 CAD-1, Inc.
Welcome to CAD
Civil Engineering designs are just a small part of a large world. Even in a
discipline embedded in coordinate systems, the people creating the designs
may know little (or nothing) about coordinate systems.
303.427.2231 | [email protected] | www.cad-1.com | ©2013 CAD-1, Inc.
CAD and Coordinates
CAD is based on Cartesian Coordinates (X,Y,Z) – Often plans are started
from an arbitrary location (0,0,0)
Even if survey control is established, it
is used as a BASE point (Benchmark).
Survey BASE points are usually
established on a project by project basis
and are frequently not tied to any GIS
coordinate system
CAD Coordinate Systems can be ignored, misrepresented or applied
CAD Coordinate Systems are typically metadata
303.427.2231 | [email protected] | www.cad-1.com | ©2013 CAD-1, Inc.
CAD and GIS– GRID vs. GROUND
Even if state plane control IS established – the project is designed and
drafted in GROUND units.
Survey control
point in State
Plane 0,0
100’
303.427.2231 | [email protected] | www.cad-1.com | ©2013 CAD-1, Inc.
Grid to Ground Conversion
Translating coordinate systems (especially Grid
to Ground) can be mathematically daunting
303.427.2231 | [email protected] | www.cad-1.com | ©2013 CAD-1, Inc.
Grid to Ground Conversion
Linear distortion due to Earth curvature
Grid length greater
than ellipsoidal length
(distortion > 0)
Ellipsoid
surfaceProjection
surface
(secant)
Maximum projection zone
width for balanced positive
and negative distortion
Grid length less than
ellipsoidal length
(distortion < 0)
Really, the only important thing to understand is that CAD (GROUND) and
GIS (GRID) are two different distances
303.427.2231 | [email protected] | www.cad-1.com | ©2013 CAD-1, Inc.
Grid to Ground Simplified
Simply – Grid distances are TYPICALLY less than grid.
99.974’
303.427.2231 | [email protected] | www.cad-1.com | ©2013 CAD-1, Inc.
CAD and GIS – Coordinate Conversion
CAD can use two methods to convert drawings to projected coordinate
systems:
Scale
Easiest to use
Requires a BASE POINT
This SHIFTS the data ~900’ from it’s original location
Makes integration of GIS data impossible
Is frequently used by Dept. of Transportation agencies
Programmatic conversion
Most accurate system
Allows for integration of GIS data
Requires creation of custom (ground) coordinate system)
Needs EDUCATION
303.427.2231 | [email protected] | www.cad-1.com | ©2013 CAD-1, Inc.
CAD and GIS – Coordinate Conversion
Taking a city map and a small project. The black linework is BEFORE
applying a Grid to Ground scale factor of 1.00026 (Denver area). The red
linework is scaled with a base point of (0,0) – the default location. The
linework is scaled correctly – but is now ~900’ from where it started. Keep
in mind that state plane coordinates are in the MILLIONS of feet – a base
point of (0,0) is in Utah somewhere…
303.427.2231 | [email protected] | www.cad-1.com | ©2013 CAD-1, Inc.
CAD and GIS – Questions
IS the CAD data GRID or Ground?
If it is GRID – HOW was the scale applied??
If it is GROUND – how will YOU apply the scale
factor??
Having the CAD file scaled by the correct factor then
MOVED to a benchmark is often the easiest approach
to using the data.
303.427.2231 | [email protected] | www.cad-1.com | ©2013 CAD-1, Inc.
CAD and GIS – Reminders
CAD is based on Cartesian Coordinates (X,Y,Z) – Often plans are started
from an arbitrary location (0,0,0)
CAD CS can be ignored, misrepresented or applied
CAD CS is typically metadata
Even if survey control is established, it is used as a BASE point
(Benchmark).
Survey BASE points are usually established on a project by project
basis and are frequently not tied to any GIS coordinate system
Even if state plane control IS established – the project is designed and
drafted in GROUND units.
303.427.2231 | [email protected] | www.cad-1.com | ©2013 CAD-1, Inc.
Award Winning CAD-1 Services
Training •Classroom Training – for upcoming schedule, visit www.cad-1.com
•Custom, In-Person, Mentoring Programs – training programs tailored to your
firm’s specific needs.
•Implementation– Assisting you in the addition of new software and workflows
into your organization
•Online Mentoring – Live mentoring and problem solving assistance delivered
over the web.
•Support – Excellent Telephone Support from CAD-1 Can Now be Combined with
Web Based Tools for Fast Problem Resolution..
Call CAD-1 at 303-427-2231 for More Information on These Services
