Re: [Qgis-user] Vector/Raster Projection Problem

[Terry Morse]

Thank you Micha and Richard.

I'm not sure what to make of the complex pattern which is emerging:

1. If I open a new project and enable on the fly projection without designating a project, then add both the vector and raster layers, they do not superimpose.
2. If I open a new project, enable on the fly projection, and set the project projection to "NAD 83: Oregon Lambert (feet)," the layers do not superimpose.
3. If I set the raster layer projection to Oregon Lambert from WGS 84, the files do not superimpose.
4. If I set the vector layer projection to Oregon Lambert while leaving the raster in WGS 84, they do superimpose.
5. I can clip the raster layer to the geographic extent of Oregon by entering the lat/long boundaries of the state gleaned from Wikipedia into the Clipper dialogue, but if I try to clip the raster by drawing a bounding box around the counties vector, I get the "Computed -srcwin falls outside raster size . . ." error, even though the layers seemingly superimpose.  It's as if I have forced them to coincide on-screen by manipulating their projections, even though they don't actually coincide.

I don't get it.

Terry

On 11/08/2012 12:09, Terry Morse wrote

I'm not sure what I've done differently, but I managed tonight to get the projections to overlap.  The counties vector layer appears to have been reprojected to WGS84, and the display projection is NAD 83 (EPSG: 2992).  I tried to duplicate this in a second instantiation of QGIS, so far unsuccessfully.  I'm going to have to experiment more.

In the interim, When I try to clip the raster file in the successful superimposition to the extent of the counties layer using the raster clipper and get the error message: Computed -srcwin falls outside raster size of 28800x19200.  Any idea what that is about?

I tried to duplicate your steps. Seems to work fine (QGIS 1.8 on WinXP OSGeo4W installer)
I downloaded the counties shapefile and loaded it into QGIS. The CRS was listed as USER:100000 (probably since the Oregon LCC projection it's not in the proj4 database.) So I left the CRS as is, and set "On-the-Fly" reprojection. Next I got one tile from GMTED (30 arcsec) and it seems to overlay the counties correctly. (I'm judging from the coastline and Columbia river, since I don't know where the actual county boundaries are in the DEM...)

Next I ran the clipper tool from the Raster menu, and again it worked as expected. The clipped DEM remained in EPSG:4326, like the original GMTED. I can send the clipped raster if it will be any help. 

Since both layers you mentioned have full CRS metadata, I think if you don't mess with the CRS of the layers, just enable OTF, it will be fine.

--
Micha

Thanks,
Terry

From: richard burcher <drownedf...@gmail.com>
Sent: Aug 10, 2012 3:49 PM
To: qgis-user@lists.osgeo.org
Subject: Re: [Qgis-user] Vector/Raster Projection Problem

Hi Terry,

You shouldn't be having such a difficult time getting them to align. I've
done similiar with SRTM/GDEM etc.

Have you projected the shapefile to wgs84 to review alignment?

Can you please put together a small subset clip of raster data for area &
the shapefile you are using. Drop me a the link from Dropbox or other
service & I will take a look over.

Cheers,

Richard

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