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I am still learning how to use coordinate systems and projections, but I hope this basic question will be easy to answer. My goal is to be able to use either QGIS or gvSIG to create a simple county map of Illinois using the base data shapefiles available from the Illinois Natural Resources Geospatial Data Clearinghouse.

I believe I need to use a state plane coordinate system such as NAD83/Illinois (East) or NAD83/Illinois (West) so that the state will look like this:

Illinois

... but not this:

Illinois wide

In QGIS, I assume that best way to get the desired look is by first setting the application's CRS Preferences and the Project Properties CRS to NAD83/Illinois (West) [EPSG code 26972], with "On the Fly" selected, then adding the shapefile. Leaving the "On the fly" option unselected causes problems. Changing the Preferences or Project CRS after adding the shape layer also causes problems.

Are my basic steps and assumptions correct?

If those basic steps are correct, why do the same steps not work in gvSIG? (The Illinois shape is displayed as the undesired "wide" version no matter what I do.)

Added later to illustrate comment on gvSIG:

Here are the dialogs I see after adding the layer:

enter image description here

In case this is relevant, here's the empty Transformations list in gvSIG:

Transformation dialog

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Please open two separate threads for the two topic: 1) gvSIG and 2) QGIS. It's really messy now. – underdark♦ Mar 6 at 14:53
Two threads now created. – syncrasy Mar 6 at 15:31

2 Answers

up vote 2 down vote

gvSIG uses the same CRS library than QGis, is called Proj4.

In order to load the data you have to:

  1. Create a view in 26971 EPSG code (I guess). See http://i.imagebanana.com/img/ardsef2u/20130304115816Seleccin.png
  2. Load your data and go to the change source transformation. See http://i.imagebanana.com/img/jwjchwo6/20130304120019Seleccin.png
  3. Select the EPSG transformation and NAD83 to 4326 (52). See http://i.imagebanana.com/img/1uwp4pub/20130304120537Seleccin.png
  4. Accept the warning
  5. That's all!enter image description here
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Is there a step missing? Specifically, between your steps 2 and 3, do I select ESPG Transformation from the Select transformation menu? When I do that, I see that my Transformations list is blank. Am I missing the Proj4 library? – syncrasy Mar 4 at 14:02
What operating system and gvSIG version are you using? When you access the view properties and the projection dialog do you see this? imageshack.us/f/402/screenshot060313081930.png – Jorge Sanz Mar 6 at 8:22
I'm using Mac OS 10.6.8 Snow Leopard, gvSIG 1.10. I've added a screenshot of my dialog windows to the original post. – syncrasy Mar 6 at 14:36
I've split off the gvSIG portion of this thread into a new discussion at gis.stackexchange.com/questions/53657/… . Please continue discussion of this issue on the new thread. – syncrasy Mar 6 at 17:07
up vote 1 down vote

If you get the "wide" version, you see coordinates in lat/lon, which is distorted. To get a right picture, you can set almost every projected as project CRS suited for your area. With a UTM or a global projection like Google Mercator EPSG:3857 give a silimar picture. The layer CRS still remains to be lat/lon EPSG:4326.

It should not matter whether you do it before or after adding the layer. "On-the-fly" should always be checked.

I'm not sure if gvSig can handle differences between layer and project CRS.

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Thanks. I think I understand. I was able to start a new project with "EPSG 4326 WGS 84" as the default CRS, add the layer, then change the Project Properties to "EPSG 26972 NAD83/Illinois (West)" to change the look from wide to narrow. And it appears that keeping "On the fly" checked in both QGIS Preferences and Project Properties is essential. Is QGIS transforming something? If so, what is being transformed? – syncrasy Mar 3 at 21:24
But I still can't get "EPSG 26972 NAD83/Illinois" to work on gvSIG. Does it have a less sophisticated transformation engine than QGIS? – syncrasy Mar 3 at 21:26
Yes, QGIS does the transforming "on-the-fly", just for rendering. I have not much experience on gvSIG. Maybe you find an answer on their mailing lists: gvsig.org/web/community/mailing-lists/directory-en/… – Andre Joost Mar 4 at 5:15
I've split off the QGIS portion of this thread into a new discussion at gis.stackexchange.com/questions/53656/… to seek help with a "transform error" that I encountered. – syncrasy Mar 6 at 17:05
I guess you meant "I encountered an error in gvSIG"? – Andre Joost Mar 6 at 19:32
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