[OSGeo-Discuss] Correct List for Newcomers
webwiz at pl.net
Tue Mar 29 14:17:04 PDT 2011
The qgis georef plugin is good with a few regrettable UI odditys. (QGIS 1.6 WIN).
1. It essentially uses brute force to distort the raster to try to make your grid control points match. If you know the projection of the source raster then there are better ways see below.
2. A trap for young players is that any method but linear will distort the raster, ie rotate or squish. None of this is made clear by the plugin.
3. For some odd reason you cant paste coords into the UI. Odd because who remembers and types 9 digit numbers.
4. Try to get an accurate vector layer of the same terrain, that has recognizable locations that match your raster, load that up, and then use the from map tool, itll be the easiest way.
Now if you know the projection of the source raster, why mess around with it. Use the QGIS | raster | warp tool which warps between two mathematically known projections, and not introduce any more noise, and assigns the source srs, and converts to geotiff all in one action.
One newbie to another mate. Theres lots to learn, allow some time or youll find it frustrating.
Bob Kerstetter wrote:
> On Mar 28, 2011, at 9:27 PM, Alex Mandel wrote:
>> On 03/28/2011 05:43 PM, Bob Kerstetter wrote:
>>> Is this the correct list for asking newbie questions?
>>> For example, I am using the decklogs from a 1940s US Navy cruiser to trace its journey's from 1942 through 1945. I know how to enter coordinates, draw lines and load maps, but where do I obtain a specific map? I need one covering the entire Pacific Ocean as it was defined during that era. I would like the map to show the Pacific and all of its islands, including small areas such as Yap and Ulithe, for example. I would also like to have a layer showing the geographic structures on the Pacific floor, such as the IBM arc. Do resources such as these exist, or do I need to create my own? I have searched the Web for answers but really don't know enough to enter search criteria correctly.
>> could you please clarify what
>> software you are using so we can direct you to the more appropriate list
>> on that?
> I am using Quantum GIS on Mac OS X.
>> Of the course the other approach is to more generally ask what software
>> should you be using for your particular use case.
> Is QGIS the correct software to use? It allows me to plot locations and draw line between them.
>> Personally if you know where to access a paper
>> reproduction I would say digitize it, georeference it and use that as
>> your base map.
> How do you georeference a map? I have paper maps.
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