[Qgis-user] getting square raster images from MODIS tiff files into QGIS

[Nicolas Cadieux]

Hi, 
The Utm projection you are using is in meter so its easy to make square.  The MODIS tiff is probably in wgs84 so that would be in latitude and longitude.  In wgs84, the square will become a trapezium specially when working over long distances or close to the pole. 
Make sure "projection on the fly" is activated and open both layers.  Change the project projection to UTM and you will have a square.  If your raster looks distorted, you will need to reproject the vector layer (UTM) to your raster projection... 
That is easy to do but first, you need to add vertex to the square or else you only have 4 corner points to work with. 
You need to "complexify" the polygon.  Look in the vector tools. Add some point (like a 1000) then reproject the vector UTM file to the MODIS projection.  The vector should stop disappearing but it will be rectangular in shape.  
If you want a square in wgs84 but need to draw it in UTM coordinates, you will need to figure out how many meters you have in one arc-second longitude and how many meter you have  in one arc-second latitude for that position in space.  You will then draw a rectangle in UTM that will look square in WGS84. 
Nicolas Cadieux M.Sc. 
Les Entreprises Archéotec inc.  
8548, rue Saint-Denis Montréal H2P 2H2 
Téléphone: 514.381.5112  Fax: 514.381.4995 
www.archeotec.ca 
On Apr 14, 2015 1:13 AM, "Don McNeil [via OSGeo.org]" <ml-node+s1560n5201200h61 at n6.nabble.com> wrote: 

	Dear QGIS Gurus: My problem is that, having already created vector layers for a region in separate sub-windows of QGIS, when I create an additional layer for a raster image by opening a MODIS TIFF file for the same region, it appears as a trapezium rather than a rectangle, and when I try to convert it to a rectangle by specifying the UTM location, the vector images disappear. So I can't show both the squared raster image and the vector images together. I emailed a friend who uses other GIS software (including ArcGIS, ERDAS and IDRISI) and he suggested that I might need a process of rectification for adjusting the shape and position of the image to the real position instead of just changing the coordination. If so, does Quantum GIS have a function to do that? kind regards....Don 
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