[Qgis-user] Satellite Image Geo-referencing

[Nicolas Cadieux]

Hi,
I am not sure what you mean about the second part of your question. Can 
you add a screen shot with more details?  (You may have to add a nodata 
value to the raster to reset the scale.)

As for the first part, if you use and interpolation method with, for 
example a 3 meter search radius, then you will most likely finish with a 
raster that is 3m. wider on all sides.  If your area  is a square or a 
rectangle, then you can select an x min, x max, y min, ymax (Raster/ 
Interporlation Plugin).  If you are using Gdall_Grid 
(Raster/analysis/Grid) you can manually add the same bounding box 
extant  (http://www.gdal.org/gdal_grid.html)  with the -txe and -tye 
configurations.  Click on the yellow pen and on the Help button for more 
information.  You can also use the Clipper tool (raster/extraction/clipper).

If your area boundary is not square, you can manually cut back the 
raster by using the following method.
1: Creating a mask:
- Create a new polygon vector file with a new field that will receive 1 
and 0.  You will have to create a polygon with the area you what to keep 
(1) and for areas you need to cut (0)
- Can use tools like "vector/research tools/polygon from layer extent" 
to help out.
- convert the vector to a raster (same size and resolution as your 
interpolated result) "raster/conversion/vector to raster"

2: Use the Clipper tool or simple raster math to clip the extant by 
multiplying both rasters.  Area with "0" will be set to "0" and Area 
with "1" will keep there values.  You may have to add no value data to 
make it work "right click on layer/ save raster layer as/ No data values..."

Hope this helps.
Nicolas



Le 2015-04-29 03:50, Suvendu Roy [via OSGeo.org] a écrit :
> Respected User of Q-GIS,
> I have an question on image clipping of an interpolation map.
> After prepare an interpolation map using point vector, the extension 
> of interpolated result cross the study area boundary, even though, the 
> sample points are within the study area.
> Please help me to guide to prepare an interpolation map, which should 
> be restricted within the study area only, not fill the outside also.
> In the same map, when i use IDW interpolation method, in the legend 
> the range value of the original attribute also changes (become low), 
> how can i solve all these problem?
>
> /*Suvendu Roy*
> Junior Research Fellow-UGC, /
> /Department of Geography, University of Kalyani, /
> /Kalyani, Nadia-741235/
> /Alternative Mail Id: [hidden email] 
> </user/SendEmail.jtp?type=node&node=5203411&i=0>
> Mob. +91 9153128612/
>
> On Tue, Mar 31, 2015 at 4:02 PM, Suvendu Roy <[hidden email] 
> </user/SendEmail.jtp?type=node&node=5203411&i=1>> wrote:
>
>     Respected User,
>     Is the full version of HEC-GeoRAS can be patched with the Qgis,
>     present, Q-RAS help to get cross-section data, but it can't export
>     the modeled data to the GIS for floodplain mapping.
>
>     /*Suvendu Roy*
>     Junior Research Fellow-UGC, /
>     /Department of Geography, University of Kalyani, /
>     /Kalyani, Nadia-741235/
>     /Alternative Mail Id: [hidden email]
>     </user/SendEmail.jtp?type=node&node=5203411&i=2>
>     Mob. +91 9153128612/
>
>     On Tue, Mar 10, 2015 at 3:51 PM, Suvendu Roy <[hidden email]
>     </user/SendEmail.jtp?type=node&node=5203411&i=3>> wrote:
>
>         Dear Q-GIS users, I want to work on "image to image"
>         geo-referencing e.g. ASTER to Topographical Sheet) for my
>         research work, but Icant's get the option for it. Actually, I
>         have an ASTER DEM image and Iwant to register it according to
>         mybase map. Please guide me for it. Thank You in advanced.
>         /*Suvendu Roy*
>         Junior Research Fellow-UGC, /
>         /Department of Geography, University of Kalyani, /
>         /Kalyani, Nadia-741235/
>         /Alternative Mail Id: [hidden email]
>         </user/SendEmail.jtp?type=node&node=5203411&i=4>
>         Mob. +91 9153128612/
>
>
>
>
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