3

I have a series of raster map images that I would like to use in QGIS and overlay some simple GPX routes over the top to produce a custom map image.

This is all quite new to me so please bare with me. I am struggling to get the raster image and GPX layers to display on the same map. My suspicion is that the two layers are using different projections or coordinate systems (excuse me if this the incorrect terminology).

When both layers are displayed in QGIS, they are not even visible in the same display. The coordinates displayed for each are wildly different and are not of the same magnitude.

I'd like to know how to covert the images I have so that can use them with GPX files. For information, these are Australian NSW Lands Department maps as provided with the TopoView 2006 DVD product.

gdainfo in the raster image reports:

./gdalinfo ~/Desktop/89313s.ecw 
Driver: ECW/ERDAS Compressed Wavelets (SDK 3.x)
Files: /Users/jon/Desktop/89313s.ecw
Size is 6168, 3808
Coordinate System is:
PROJCS["MGA56",
    GEOGCS["GEOCENTRIC DATUM of AUSTRALIA",
      DATUM["GDA94",
          SPHEROID["GRS80",6378137,298.257222101]],
      PRIMEM["Greenwich",0],
      UNIT["degree",0.0174532925199433]],
  PROJECTION["Transverse_Mercator"],
  PARAMETER["latitude_of_origin",0],
  PARAMETER["central_meridian",153],
  PARAMETER["scale_factor",0.9996],
  PARAMETER["false_easting",500000],
  PARAMETER["false_northing",10000000],
  UNIT["Meter",1]]
Origin = (220464.635367600014433,6304336.451381999999285)
Pixel Size = (4.000000000000000,-4.000000000000000)
Corner Coordinates:
Upper Left  (  220464.635, 6304336.451) (149d59'44.79"E, 33d21'50.07"S)
Lower Left  (  220464.635, 6289104.451) (149d59'27.75"E, 33d30' 3.98"S)
Upper Right (  245136.635, 6304336.451) (150d15'38.36"E, 33d22'12.14"S)
Lower Right (  245136.635, 6289104.451) (150d15'22.81"E, 33d30'26.17"S)
Center      (  232800.635, 6296720.451) (150d 7'33.40"E, 33d26' 8.35"S)
Band 1 Block=6168x1 Type=Byte, ColorInterp=Red
Overviews: 3084x1904, 1542x952, 771x476, 385x238
Band 2 Block=6168x1 Type=Byte, ColorInterp=Green
Overviews: 3084x1904, 1542x952, 771x476, 385x238
Band 3 Block=6168x1 Type=Byte, ColorInterp=Blue
Overviews: 3084x1904, 1542x952, 771x476, 385x238

Extract from GPX is as follows:

<?xml version="1.0" encoding="UTF-8"?>
<gpx version="1.1" creator="Garmin Connect"
  xsi:schemaLocation="http://www.topografix.com/GPX/1/1        http://www.topografix.com/GPX/1/1/gpx.xsd http://www.garmin.com/xmlschemas/GpxExtensions/v3 http://www.garmin.com/xmlschemas/GpxExtensionsv3.xsd http://www.garmin.com/xmlschemas/TrackPointExtension/v1 http://www.garmin.com/xmlschemas/TrackPointExtensionv1.xsd"
  xmlns="http://www.topografix.com/GPX/1/1"
  xmlns:gpxtpx="http://www.garmin.com/xmlschemas/TrackPointExtension/v1"
  xmlns:gpxx="http://www.garmin.com/xmlschemas/GpxExtensions/v3"  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <metadata>
    <link href="connect.garmin.com">
      <text>Garmin Connect</text>
    </link>
    <time>2010-08-30T21:03:24.000Z</time>
  </metadata>
  <trk>
<name>Canberra to 'Castle Day 3</name>
    <trkseg>
      <trkpt lon="150.05063133314252" lat="-33.67591420188546">
        <ele>1030.0</ele>
        <time>2010-08-30T21:03:24.000Z</time>
        <extensions>
          <gpxtpx:TrackPointExtension>
        <gpxtpx:atemp>2.0</gpxtpx:atemp>
          </gpxtpx:TrackPointExtension>
        </extensions>
      </trkpt>
      <trkpt lon="150.05062630400062" lat="-33.67588419467211">

Thanks for any help.

Cheers.

Jon.

2

The layers should align when you set the project CRS to "MGA56" (same as the raster) and enable on-the-fly reprojection.

  • 1
    Starting from QGIS 1.7 it would be possible to reproject on the fly also rasters. – Giovanni Manghi Jun 12 '11 at 17:03
  • Yes, once it's released :D – underdark Jun 12 '11 at 17:16
  • i have a problem with this.. when i enable otf projection, after that my raster map escape on some other coordinating system, but the gpx reproject itself in system of raster map from before. how to solve that? i hope that you guys unterstood me and sorry because my language. – mihailo Sep 8 '11 at 14:01
  • Which CRS did you use for raster, gpx and project settings, @user4169? – underdark Sep 8 '11 at 15:40
  • i use for raster MGI/balkans zone 6 ............................ – mihailo Sep 8 '11 at 16:11
1

user4169: When you load a raster QGIS will set its CRS to the current project CRS (probably unprojected WGS84 unless you changed it), and then when you change the project CRS and enable on-the-fly projection QGIS interprets the raster as a WGS84 raster and tries to project it from WGS84 to MGA56, which means that it'll end up in the completely wrong place on the map. If you change the CRS of the raster layer to MGA56 it should work as expected.

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