LISTSERV mailing list manager LISTSERV 16.5

Help for CODE4LIB Archives


CODE4LIB Archives

CODE4LIB Archives


CODE4LIB@LISTS.CLIR.ORG


View:

Message:

[

First

|

Previous

|

Next

|

Last

]

By Topic:

[

First

|

Previous

|

Next

|

Last

]

By Author:

[

First

|

Previous

|

Next

|

Last

]

Font:

Proportional Font

LISTSERV Archives

LISTSERV Archives

CODE4LIB Home

CODE4LIB Home

CODE4LIB  December 2007

CODE4LIB December 2007

Subject:

Re: [Metadatalibrarians] Georeferencing with open source tools

From:

Keith Jenkins <[log in to unmask]>

Reply-To:

Code for Libraries <[log in to unmask]>

Date:

Fri, 7 Dec 2007 11:25:08 -0500

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (89 lines)

Hi, Clay.

Your details are daunting, but I'll try to help :)

Since your map is lucky enough to have them, I'd suggest using the
intersections of the latitude/longitude lines as your control points.
Besides offering nice round numbers, they are evenly spaced across the
map.  Try it first with every 10 degrees, and if that isn't good
enough, go with every 5 degrees.

The projection of the original map is not so important in this
process, since you are using control points.  And the datum really
doesn't matter here: the difference between WGS84 and NAD83 is going
to be less than the width of the lines on a map of this scale.  So I
wouldn't worry too much about the map having been folded, either.

As for relying on open source tools, you should be in good hands with
GDAL, GeoServer, and OpenLayers.

Good luck!

Keith


On Dec 5, 2007 11:40 AM, Clay Redding <[log in to unmask]> wrote:
> Hi all,
>
> This is for any of you GIS specialists out there!  Please help me if
> possible, and feel free to email backchannel since this is somewhat
> off-topic for both listservs.  I'm a bit of a newbie to doing GIS and
> geomatics work.  As part of an effort to enable geographical browse,
> search, and retrieval for some digital projects at LoC, I'm trying to
> georeference a historical map [1] of the continental United States,
> as well as parts of Canada and Mexico.
>
> I plan to serve the map as a WMS layer, then pull it in using the
> OpenLayers JS library inside our site for the end user navigation.  I
> aim to "georectify" the image so that it can be placed over top of a
> more modern map layer along the lines of Yahoo! Map Mixer [2] or
> MetaCarta's Rectifier [3].  At this point I'll merely work with
> raster data, since vector data isn't needed yet.
>
> Here are the requirements this project:
>
> -- I am required to use this historical map as the basis of my work,
> as opposed to something more modern like Google Maps on its own.
>
> -- I have to use open source tools, as I don't have ESRI tools at my
> disposal.  Thus far my toolkit includes: Quantum GIS and uDig, GDAL,
> PROJ.4, PostGIS, GRASS (although I'm not skilled at GRASS), and
> Geoserver with PostGIS for serving the content.
>
> Here's what I (think I) know, based on meeting with a GIS specialist
> here at LC who has since departed for a new job:
>
> -- The map has an Albers Equal Area projection, with NAD83 datum, and
> GRS80 spheroid. (In proj or cs2cs: +proj=aea +lat_1=20 +lat_2=60
> +lat_0=40 +lon_0=-96 +x_0=0 +y_0=0 +ellps=GRS80 +datum=NAD83 +units=m
> +no_defs).  She determined this by opening the map in ArcGIS, and
> it's ESRI Well Known Text (WKT) 102003.
>
> -- The physical map was once folded, and might be throwing off some
> of the measurements.
>
> Using both gdal_translate (on the shell) and Quantum GIS (GUI)
> georeference plugin, I've plotted upward of 40 ground control points
> throughout the USA, Canada, Mexico, and Cuba.  I've found the WGS84
> latlong coordinates on databases such as the GNIS as well as the
> USGS.  US points are plotted to 5 decimal points of accuracy.
> International points have 2 decimal points.  I run these through
> cs2cs to convert latlong WGS84 to the Albers/NAD83 coordinates.
> After warping the image based on these Albers/NAD83 ground control
> points, I'll still end up as much as 50 miles off on my north/south
> results, and around 3-4 miles east/west.
>
> My question primarily has to do with best practices for
> georeferencing a map that covers such a large area like North
> America.    Have I used enough points?  Should I use more?  Or have I
> already committed overkill?  Or, do I even have the right projection
> information?  Would I be better off using some other tool(s)?
>
> Thanks for any help you can provide.  I can provide more info, the
> raster image, etc., if needed.
>
> Clay
>
> [1] http://hdl.loc.gov/loc.gmd/g3301p.ct001842
> [2] http://maps.yahoo.com/mapmixer
> [3] http://labs.metacarta.com/rectifier/

Top of Message | Previous Page | Permalink

Advanced Options


Options

Log In

Log In

Get Password

Get Password


Search Archives

Search Archives


Subscribe or Unsubscribe

Subscribe or Unsubscribe


Archives

October 2024
September 2024
August 2024
July 2024
June 2024
May 2024
April 2024
March 2024
February 2024
January 2024
December 2023
November 2023
October 2023
September 2023
August 2023
July 2023
June 2023
May 2023
April 2023
March 2023
February 2023
January 2023
December 2022
November 2022
October 2022
September 2022
August 2022
July 2022
June 2022
May 2022
April 2022
March 2022
February 2022
January 2022
December 2021
November 2021
October 2021
September 2021
August 2021
July 2021
June 2021
May 2021
April 2021
March 2021
February 2021
January 2021
December 2020
November 2020
October 2020
September 2020
August 2020
July 2020
June 2020
May 2020
April 2020
March 2020
February 2020
January 2020
December 2019
November 2019
October 2019
September 2019
August 2019
July 2019
June 2019
May 2019
April 2019
March 2019
February 2019
January 2019
December 2018
November 2018
October 2018
September 2018
August 2018
July 2018
June 2018
May 2018
April 2018
March 2018
February 2018
January 2018
December 2017
November 2017
October 2017
September 2017
August 2017
July 2017
June 2017
May 2017
April 2017
March 2017
February 2017
January 2017
December 2016
November 2016
October 2016
September 2016
August 2016
July 2016
June 2016
May 2016
April 2016
March 2016
February 2016
January 2016
December 2015
November 2015
October 2015
September 2015
August 2015
July 2015
June 2015
May 2015
April 2015
March 2015
February 2015
January 2015
December 2014
November 2014
October 2014
September 2014
August 2014
July 2014
June 2014
May 2014
April 2014
March 2014
February 2014
January 2014
December 2013
November 2013
October 2013
September 2013
August 2013
July 2013
June 2013
May 2013
April 2013
March 2013
February 2013
January 2013
December 2012
November 2012
October 2012
September 2012
August 2012
July 2012
June 2012
May 2012
April 2012
March 2012
February 2012
January 2012
December 2011
November 2011
October 2011
September 2011
August 2011
July 2011
June 2011
May 2011
April 2011
March 2011
February 2011
January 2011
December 2010
November 2010
October 2010
September 2010
August 2010
July 2010
June 2010
May 2010
April 2010
March 2010
February 2010
January 2010
December 2009
November 2009
October 2009
September 2009
August 2009
July 2009
June 2009
May 2009
April 2009
March 2009
February 2009
January 2009
December 2008
November 2008
October 2008
September 2008
August 2008
July 2008
June 2008
May 2008
April 2008
March 2008
February 2008
January 2008
December 2007
November 2007
October 2007
September 2007
August 2007
July 2007
June 2007
May 2007
April 2007
March 2007
February 2007
January 2007
December 2006
November 2006
October 2006
September 2006
August 2006
July 2006
June 2006
May 2006
April 2006
March 2006
February 2006
January 2006
December 2005
November 2005
October 2005
September 2005
August 2005
July 2005
June 2005
May 2005
April 2005
March 2005
February 2005
January 2005
December 2004
November 2004
October 2004
September 2004
August 2004
July 2004
June 2004
May 2004
April 2004
March 2004
February 2004
January 2004
December 2003
November 2003

ATOM RSS1 RSS2



LISTS.CLIR.ORG

CataList Email List Search Powered by the LISTSERV Email List Manager