Altering the basic geometric structure of the map can range from trivial to difficult.  Two weeks ago, we looked at the conceptual base of projections--the context in which our maps exist.  Last week we saw applications of remote sensing.  This week, we consider possible solutions to geometric alteration of maps that lie between the trivial (just go to View|Properties and change the projection and everything works well) to the difficult (find a technical consultant with more software and machinery than is routinely available in the standard computing environment).

Note:  if you are loading map files from a CD, be sure to remove the "read-only" mark from the files.  Go to Windows Explorer, File|Properties and take the check out of the box.

Concepts to look for:  spatial transformation; scale; distance; hierarchy; absolute and relative location--others?

  • View|Properties--change the projection and all works--use the Custom settings to change longitude on which the view is centered, and so forth.
  • Use the extension called "Projector."
    • Activate the extension; it is not part of the default extension package installed to work directly in ArcView
      • To become active, an extension must be placed in the following subdirectory:  ...\esri\Av_gis30\arcview\ext32
      • Find the extension--extensions have the file extension *.avx--look in ...\esri\Av_gis30\arcview\samples\ext  and take a copy of prjctr.avx (and .apr if you want) to the appropriate location.
      • In ArcView go to File|Extensions and click on the extension called Projector; doing so will activate a button with an up-arrow and four dots.
    • Examples using SEMCOG map and City of Detroit map.  Simple change does not appear to work, although many possibilities could be tried.  It is known that the SEMCOG map is State Plane 1983, NAD83, units=feet, and fips=2113 (South zone designation).
  • Projector changes only projections; it does not change the datum--the underlying reference system  against which measurements are directly referenced.  Thus, if Projector does not do the job, try something else.  One other extension, and this one is directly installed to work (by default), is the ArcView Projection Utility--activate the extenion in File|Extensions
    • PRIOR TO USING THIS EXTENSION, MAKE SURE TO DISABLE ANY VIRUS CHECKING SOFTWARE ON YOUR MACHINE; IF YOU DO NOT DO SO, THE PROGRAM IS VERY LIKELY TO "HANG" AND GET "STUCK."  Thus, if you find that you are using this extension and it is taking forever to work, close it and go back and make sure that your virus checking software has been disabled.
    • If you are not willing to disable your virus checking software, or if you are working in an environment that will not allow you to disable it, consider using something other than the Projection Utility.
    • Example converting NAD27 to NAD83, state plane coordinates.  This package does allow for datum shifts so that is one reason to consider disabling the virus checking software.  I will not do that on my laptop, however.
  • A script is a small program that functions, to some degree, as an extension.  ArcView comes with a number of scripts that perform various tasks.  One of them is a script that permits one to slide maps around, horizontally or vertically.  As long as displacement is the only issue, and distortion of shape is not involved, this tool can be quite useful in moving maps around in the View.
    • Activate the script called xyshift.ave
      • Make the View window an intermediate size and go back to the window that lists the ArcView table of content in the left frame.
      • Scroll down and click on Scripts; double click Scripts. 
      • You should now see a new blank window.  Click on the Script pull-down menu and choose "Load text file."
      • Navigate to the sample scripts that come with ArcView:  ...\Esri\Av_gis30\ArcView\Samples\scripts  and open up the file called xyshift
      • You should now see a computer program in what was the blank window.
    • In order to "run" the script you must first "compile" it.
      • Click on the View window; be sure to activate the appropriate shape file.  Be sure, however, to click on the View window even if the appropriate shape file is already active; failure to do so may produce an error message later.
      • Now click on the Script window
        • Click on the Compile button (check mark)--notice that the button just to the right of the Compile button is not active prior to clicking on Compile.
        • After clicking on the Compile button, the button to the right becomes active (it has a stick figure "running").  This newly-activated button is the Run button:  click on it.
        • Now the action will prompt you for various items to input.  If you need to go back to the map to figure them out, do so; the script has been compiled and should continue to Run well.
    • Conceptually, this script executes a geometric tranformation, called "translation" (literally (L.), "sliding across").  Translation is a "rigid motion"--it does not alter shape, just slides fixed images.
    • Examples using City of Detroit data (freeways) and SEMCOG data (minor civil divisions).
  • Blue Diamond extension--builds a "world" file with which to "register" vector maps to raster images.  This extension may alter shape--it is like building a quilt--tack the image to the map in a number of places and what is left in between may be a bit puffy--not fit perfectly with the map.  Best fit occurs nearest registration points.
    • Find the extension and install it; it is called register.avx and is available from the linked source
    • Open up an image in ArcView--if it is not in .jpg format be sure to save it in that format.  If using *.sid files, you will have had to make sure the MrSid extension is loaded.  PhotoShop does not load Mr.Sid files; to load them in PhotoShop, you would need to go to the web to get an extension to enable you to do so.  Thus, try saving the MrSid file as a .jpg directly from ArcView (there will be considerable loss in resolution).
    • Then, set the View back to an intermediate size. 
    • Go to Explorer and create a new folder--put the files you want to use, shape files and related files as well as the .jpg you just created, into this new folder.
    • Go back to ArcView and click on the blue diamond.  Choose your .jpg when requested to choose an image.  Then, choose your map file.
    • Start with the .jpg and find a point in the image that you can also find on the map--the intersection of two major roads; the intersection of a bridge with the shore; and, so forth.  Click on the little flag symbol at the left end of the array of buttons. Choose a point on the image; then choose the corresponding point on the map.  You may wish to maximize the window or zoom in to see better.  Then back to the image, and so forth.  Execute this procedure at least six times to tack the image to the map--the image will be stretched to "fit" the map.  These points are called "registration" or "control" points.  Choosing more may be good, but only if you can locate them with fair accuracy on both the image and the map. 
    • Once all the control points have been set, reduce the View window back to intermediate size.  Double click on the words under Tables--Ground Control Points--to open up the table you have created.  The last column is labelled RMS (Root Mean Square error) and all entries will be 0.  Click on the C button to calculate the RMS.  If you have more than 6 entries in the table, discard any very high values--hit the calculate button again.  Close the table.  Re-open the table and look at it and hit C again.
    • Now, click on the pencil symbol at the top--it will now write a "world" file that carries the text that tells the image where to place itself in relation to the map.  Let the software decide its own name (or you choose one--it doesn't really matter)--just keep all your files in the same folder.
    • Now the software will shut down the open files.  Reopen the ones you had open and you will see your freshly aligned image!  If there is too much distortion, try again!
  • Last option--find your technical support staff.  They may reproject files for you using ArcInfo (too expensive for the standard user).
  • Of critical importance--know information about your files!  What projection they are, what datum they use, what units they use and any other key factors.
  • Related links--if you want more scripts and extensions than the set that comes with ArcView look on the web--build a collection--if someone offers you one, take it.  Even if it is not useful to you now, it may become useful later on (as with maps!).  Join the ArcView Users' Group--if you are prepared to get a lot of e-mail!  Join through ESRI.
  • Working in computing environments--complex systems in which the characteristics of the individual element of the system do not necessarily transform, or map, to the characteristics of the whole system.  So--look for what is good and works well within your own computing environment and supplement it as needed from your own imagination and resource base.