Changes between Version 107 and Version 108 of WKTRasterTutorial01


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Timestamp:
01/17/11 12:33:08 (14 years ago)
Author:
pracine
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  • WKTRasterTutorial01

    v107 v108  
    298298== Making buffers around the caribou points ==
    299299
    300 This operation is also very straightforward for any casual PostGIS user. The caribou point table is in a spatial reference system suitable for measurements in meters so we can build our buffers in this system and then convert them to the raster one later in order to intersects them. We will make 1 km buffers around our points and save them as a new table. We do this operation in a pgAdmin III query window (not in OpenJUMP):
     300This operation is also very straightforward for any casual PostGIS user. The caribou point table is in a spatial reference system suitable for measurements in meters (32198) so we can build our buffers in this system and then convert them to the raster one (4326) later in order to intersects them. We will make 1 km buffers around our points and save them as a new table. We do this operation in a pgAdmin III query window (not in OpenJUMP):
    301301
    302302{{{
    … …  
    313313}}}
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     315The buffers have and oval shape because they are displayed in a non-projected spatial reference system (WGS 84) to fit with the raster layer. In the database they were created in a projected coordinate system (NAD 83/Quebec Lambert) and are truly circle all of equal area. You can observe that southern buffers, again because they are displayed in a non-projected spatial reference system, are smaller (less wide) than the northern ones. If we would display everything in NAD 83/Quebec Lambert, they would all be of the same circle shape. But we can't do this because our raster are in WGS 84 and PostGIS do not support raster reprojection yet.
     316 
    315317We then reproject our buffers to WGS 84 so we can intersect them with our raster coverage:
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