Problems with loading a large raster into QGIS
March 13, 2011 2:06 PM Subscribe
I am having trouble adding a large jpg map (15mb) into Quantum GIS to georeference it, also I don't actually know how to georeference in QGIS.
I have updated to QGIS 1.6, and I have a relatively fast computer (Intel Core i5 with 4gb Ram). But every time I try to load this image as a raster, the program simply stalls. It doesn't crash, it's still thinking - but it will sit and think for 1/2 an hour.
It seems to be stalling because there is no coordinate system associated with the image and because of the size.
I am going to try to see if I can reduce the side of the image without losing critical detail, but I was hoping I might find some advice here about loading a yet-to-be-georeferenced raster into QGIS.
Also, once I get the image in, how can I georeference it? I know there are tools, but the pdf manual seems to be talking about inserting co-ordinates only. I was hoping to georeference it by tagging points to points on another raster or vector layer, and simply importing the coordinate system. It currently has no modern coordinate system - it's a map from 1658. I had previously matched it up roughly to the OS Survey and did only a first-level transformation (re-orientation without distortion), so that I can read the features. Exact spacial accuracy is not important to me; I am using GIS so that I can convert this raster map into vector maps which can be displayed separately for qualitative analysis. (the whole has too much information).
I have previously georeferenced this map in ARCGIS, but as far as I know the raster files created by the ESRI program are not compatible with QGIS. (If they are, that would save a huge amount of work).
I have updated to QGIS 1.6, and I have a relatively fast computer (Intel Core i5 with 4gb Ram). But every time I try to load this image as a raster, the program simply stalls. It doesn't crash, it's still thinking - but it will sit and think for 1/2 an hour.
It seems to be stalling because there is no coordinate system associated with the image and because of the size.
I am going to try to see if I can reduce the side of the image without losing critical detail, but I was hoping I might find some advice here about loading a yet-to-be-georeferenced raster into QGIS.
Also, once I get the image in, how can I georeference it? I know there are tools, but the pdf manual seems to be talking about inserting co-ordinates only. I was hoping to georeference it by tagging points to points on another raster or vector layer, and simply importing the coordinate system. It currently has no modern coordinate system - it's a map from 1658. I had previously matched it up roughly to the OS Survey and did only a first-level transformation (re-orientation without distortion), so that I can read the features. Exact spacial accuracy is not important to me; I am using GIS so that I can convert this raster map into vector maps which can be displayed separately for qualitative analysis. (the whole has too much information).
I have previously georeferenced this map in ARCGIS, but as far as I know the raster files created by the ESRI program are not compatible with QGIS. (If they are, that would save a huge amount of work).
Response by poster: I would love to just import as GeoTiff, since then I wouldn't have to redo a bunch of work creating vector files based on this raster. But I no longer have access to a copy of ESRI, unless I can beg/borrow access from someone at a local university. Is there any freeware program which can do the conversion? Or should I just try to get the shapefiles to a loaded university computer?
I also have the jpg and jgw - they are two of the several files that make up the ESRI raster file. But I don't understand how to import them into Quantum GIS.
posted by jb at 6:55 PM on March 13, 2011
I also have the jpg and jgw - they are two of the several files that make up the ESRI raster file. But I don't understand how to import them into Quantum GIS.
posted by jb at 6:55 PM on March 13, 2011
Do "Open Raster Layer", then chose file type "[GDAL] Jpeg/Jfif". Open the jpeg, and it will try to pick up the jgw if it can find it in the same folder.
posted by scruss at 7:34 PM on March 13, 2011
posted by scruss at 7:34 PM on March 13, 2011
Can't help you with the JPG loading problem, it sounds odd. But georeferenceing in Quantum GIS has very little to do with ordinary QGIS use; the Georeference plugin stands entirely alone. Check the QGIS manual section 10.8 for instructions on the georeference plugin.
Quick guide: open Plugins/Georeferencer/Georeferencer, then File/Open Raster (in the georeference plugin), then Edit/Add Point to add your tie points. Then File/Start Georeferencing. You have some options to set, see the manual for details. You'll want to save your GCP points by hand too, so you don't lose your work.
posted by Nelson at 8:37 PM on March 13, 2011
Quick guide: open Plugins/Georeferencer/Georeferencer, then File/Open Raster (in the georeference plugin), then Edit/Add Point to add your tie points. Then File/Start Georeferencing. You have some options to set, see the manual for details. You'll want to save your GCP points by hand too, so you don't lose your work.
posted by Nelson at 8:37 PM on March 13, 2011
Response by poster: Is the jgw file where the spacial information is? Because I had already georeferenced this map in ArcMap 9.3, but now loading ArcEditor 10 (what ESRI will allow me to demo) it recognises the files as a raster dataset, but won't load it (saying there is no spacial coordinates). ArcGlobe or whatever they are calling it now doesn't seem to like it; I may have to pirate an old copy of Arcmap 9.2 or 9.3, because it looks like they've done an idiotic "update" that broke their program.
Meanwhile, Quantum GIS still won't load the jpg; I set it to "[GDAL] Jpeg/Jfif". There is a jgw file, though it is only 1kb. It's in the same folder.
posted by jb at 10:11 PM on March 13, 2011
Meanwhile, Quantum GIS still won't load the jpg; I set it to "[GDAL] Jpeg/Jfif". There is a jgw file, though it is only 1kb. It's in the same folder.
posted by jb at 10:11 PM on March 13, 2011
jgw world files are very small; just a six line text file. If you're running QGis via OSGeo4W, open up the msys shell and type
gdalinfo file.jpg
If you get stuff about origins and pixel sizes that seem to make sense, then the world file is being picked up okay.
Alternatively, memail me with a link to the files and I'll see what I can do.
QGis is usually pretty quick at moving large rasters about. I routinely sling about giant, multi-gigabyte orthophotos, and it's a ton faster that Manifold.
posted by scruss at 12:17 PM on March 14, 2011
gdalinfo file.jpg
If you get stuff about origins and pixel sizes that seem to make sense, then the world file is being picked up okay.
Alternatively, memail me with a link to the files and I'll see what I can do.
QGis is usually pretty quick at moving large rasters about. I routinely sling about giant, multi-gigabyte orthophotos, and it's a ton faster that Manifold.
posted by scruss at 12:17 PM on March 14, 2011
This thread is closed to new comments.
QGis's georeferencer is very good. It's under Plugins -> Georeferencer -> Georeferencer. It may attempt to warp the image too much to make it conform exactly to a modern CRS, but it's quick, and allows you to save your control points and fiddle with parameters to get the most appropriate fit.
posted by scruss at 3:00 PM on March 13, 2011