shrug-l: CAD to GIS projection issues
kwalsh at baskervilledonovan.com
Tue Oct 30 10:45:32 EDT 2007
Hi Steve, I'm in the same boat with getting many project files that are
surveyed or drawn on assumed coordinates. First off, make sure that you
ask your CAD folks to include references like street intersections,
section corners and/or monuments in the .dwg you end up with. Then
bring in the drawing file to ArcMap so you can link two points from the
.dwg to your known ortho. I have used the georeferencing tools
successfully (give or take issues with the rescale tool) quite often.
This can be a less painful process if you bookmark the location of your
.dwg and your ortho before you begin the georef. That way you don't
have to wait for the redraws from zooming in and out. If you export to
shapefile too early, some of your functionality can be limited. Turn
off all unnecessary layers in the .dwg and then re-symbolize the layers
so that they are more useful to you. This helped me a great deal in the
beginning when I wasn't familiar with working with CAD in GIS. When you
export to shapefile, only the layers that are turned on will export.
Once you create your links, then save your worldfile and update the
georef. The file should pop right in. Fine adjustments can be done with
the scale and shift tools. Hope this helps. Tripp Corbin has developed a
class on working with CAD in GIS; you might want to contact him about
training materials. I'm sure you will also hear from him on this post.
Good luck! Kristal
Kristal Walsh, GIS Specialist
449 Main St.
Pensacola, FL 32502
850-438-9662, ext. 4354
From: Steve Carbone [mailto:SCarbone at birkitt.com]
Sent: Monday, October 29, 2007 2:13 PM
To: SHRUG List
Subject: shrug-l: CAD to GIS projection issues
I have a simple request of all of you ... I need an easy way to project
CAD drawings in GIS to GIS coordinate systems.
Here is my dilemma:
I deal with multiple projects where CAD drawings are sent to me to
overlay onto DOQQs in ArcView. Now some of the CAD drawings that I get
will actually overlay onto my DOQQ, however, they are a rarity. Most of
the drawings show up in Timbuktu and my DOQQ shows up in Florida. Now,
when I extract out what I want from the CAD drawing into shapefile
format, I cannot re-project the shapefile to the coordinate system of my
choosing. I have tried to re-project the extracted shapefile by
removing the PRJ file, and then defining a new projection for the
shapefile. That has never met with success. I have resorted to
attempting to edit the shapefile and just move it on top of my DOQQ,
which sometimes meets with success, however, other times not. The CAD
designers that create these drawings have no idea what I am talking
about when I ask them to re-project their drawing from CAD (which I have
no idea if that is possible since I have never seen CAD in my life !!!)
I need an easy way to re-project the CAD extracted shapefiles that can
be replicated many times over.
people and nature
BIRKITT ENVIRONMENTAL SERVICES, INC.
PLEASE NOTE OUR CHANGE OF ADDRESS
550 N. Reo Street, Suite 105
Tampa, FL 33609
(813) 259-1085 (phone)
(813) 259-1086 (fax)
scarbone at birkitt.com
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