topic Re: Attempting to georeference a jpg image in Data Management Questions

Attempting to georeference a jpg image

DougWolfinger2 — Sat, 12 Jan 2013 23:14:47 GMT

I am trying to georeference a jpg image in ArcMap 9.3 to give it geospatial data. I have a projected map that I load in as one of the layers. When I add the map to the data view before the jpg image, the jpg image does not appear. When I add the jpg before the map, the jpg image appears, but the map seems to be zoomed in so far it looks like the whole data view is taken by one pixel. Any suggestions on how I could make this work would be appreciated. I have instructions on georeferencing, so I just need to get the image and the map properly loaded to the data view.

Re: Attempting to georeference a jpg image

T__WayneWhitley — Sun, 13 Jan 2013 11:55:23 GMT

Right...so I think you need 'Fit to Display' to get started. Your image has no spatial reference already defined, correct? (It's possible georef info has been added in error and this may need to be 'stripped' to start fresh.)

Generally, when starting with a fresh map, you should add a layer with a spatial reference defined - the data frame you add data to will 'assume' that spatial reference...meaning if you add a layer with an 'undefined' SR, the map will then assume an empty or 'unknown' coordinate system, meaning added layers cannot be 'reprojected' on the fly.

For georeferencing image with no spatial reference, centered the view in the data frame (with the proper SR) in on the general vicinity, click 'Fit to Display' on the georeferencing toolbar, and this will at least get the image in the current view where you can start entering control points. Finish the georef process, entering the control pts you need (probably using the affine transform method, more on that at the webhelp, see below)....can alternately use multiple view windows, but for most purposes 'Fit to Display' in order to get started works well, noted in the webhelp step 5 below:

Georeferencing a raster to a vector
Geodata » Data types » Rasters and images » Processing and analyzing raster data » Georeferencinghttp://resources.arcgis.com/en/help/main/10.1/index.html#//009t000000mq000000

Although the webhelp may be better at 10.x, here is the 9.3 ref:
http://webhelp.esri.com/arcgisdesktop/9.3/index.cfm?TopicName=Georeferencing%20a%20raster%20dataset

Re: Attempting to georeference a jpg image

DougWolfinger2 — Mon, 14 Jan 2013 00:02:24 GMT

Thanks! I've found I can zoom out or in on the projected map, and use Fit to Display to get the jpg image back to full size after I do that.

Re: Attempting to georeference a jpg image

DougWolfinger2 — Mon, 14 Jan 2013 01:40:04 GMT

Actually, I'm having problems. I get stuck on this step in the ArcGIS 10.1 'Georeferencing a raster to a vector' page.
4. From the Georeferencing toolbar, click the Layer drop-down arrow, and click the raster layer you want to georeference.

As a reminder, I'm using 9.3.

First I load the the referenced map, then the jpg image. At this point, the referenced map appears, but the jpg image does not. Then I click Zoom to Layer on the referenced map. Now it's time to try step 4. I click on the Layer arrow in the Georef toolbar, and the jpg image is not listed. The only layer listed in the Georeferencing Layer menu is the referenced map.

The only way to get the jpg image displayed is by clicking Zoom to Layer. That changes the Data View's coordinate system to whatever ArcMap thinks the jpg image's coordinate system might be. This is despite the fact that the coordinate system and spatial reference listed in the Properties of the jpg image is still the same as the coordinate system of the referenced map.