Hi, i'm using raster to vector (QGIS) and its taking a very very long time to process. i have converted the values of raster 0,1. can anyone suggest what is the issue or does it take really long to process
Nishant On Fri, Apr 11, 2014 at 3:36 PM, Colin D. MacLeod < [email protected]> wrote: > Thanks Saber, Micha and Carlos for your responses, > > I tried the v.to.rast.attribute route (and also v.rast.value), but > couldn't get those tool to work with my data set (and I'm still exploring > this issue and trying to work out what's going on as they look like useful > tools to be able to use). > > However, returning to the original Rasterize tool, I examined the raster > data layer which was created in more detail and found that while the > histogram was saying that the maximum value was 0.995968, when I > interrogated the individual grid cells with the Interrogate Features tool, > the values were indeed one where they should be. Thus, my problem was not > that the Rasterize tool was not working, but rather that it wasn't being > displayed correctly in QGIS. > > To deal with this, I went into the Layer Properties and under the Style > tab, I changed the maximum value from 0.995968 to 1. This made the legend > in the Table Of Contents window look a little odd, but the layer displayed > correctly, has the right value in it, and does the correct calculations > when using the raster calculator tool. > > I'm not too sure why the layer is not being displayed correctly in the > Table Of Contents window in the first place. Similarly, if I remove the > raster data layer from the my project and add it back in again, it reverts > to saying the maximum value is 0.995968 rather than 1 in the legend in the > Table Of Contents window and in the histogram for the data layer. Thus, > each time I use it in a new project, I have to manually change the maximum > number to 1. > > I don't know if this is a bug as such, or if this happens with other data > sets (it happened with both of mine - one point and one line data layer), > but it is certainly a potential pitfall for the novice user when it occurs. > > All the best, > > Colin > > > ================================================================================== > GIS IN ECOLOGY - Providing Training, Advice And Consultancy On The Use Of > GIS In Ecology > > Web: www.GISinEcology.com Email: [email protected] > > Need to ask a question about using GIS? Try the GIS In Ecology Forum: > www.GISinEcology.com/GIS_in_Ecology_forum.htm > > Books From GIS In Ecology Staff: > > An Introduction To Using GIS In Marine Biology; RRP: £44.99 > An Introduction To Using GIS In Marine Biology: Supplementary Workbook One > - Creating Maps Of Species Distribution; RRP: £19:99 > An Introduction To Using GIS In Marine Biology: Supplementary Workbook Two > - Working With Raster Data Layers; RRP: £19.99 > > If you wish to purchase these books, visit: > http://www.gisinecology.com/Book_Shop.htm > > To help the environment, please do not print out this email unless it is > unavoidable. > > ================================================================================== > > *From:* Carlos Cerdán <[email protected]> > *Sent:* Thursday, April 10, 2014 9:23 PM > *To:* [email protected] > *Subject:* Re: [Qgis-user] Problem with Rasterize (Vector to raster) tool > > Perhaps raster calculator can also help you > > Expression: > > (layer>0 and layer <= 1) > > Gives us 1 when sentence is true and 0 for false, for each cell in "layer". > > Good luck > > Carlos > > > > > 2014-04-10 9:29 GMT-05:00 Micha Silver <[email protected]>: > >> Using GRASS there are two modules you can consider. First : >> v.to.rast in=... out=... type=point use=val value=1 >> will convert points into raster cells (at the current region settings), >> where any cell that contains at least one point will be given value 1. >> >> Next: >> r.in.xyz in=... out=... method=sum >> will create a raster (at the current region settings) where each cell >> will have a value = the count of points in that cell. >> >> HTH, >> Micha >> >> On 04/10/2014 04:20 PM, Colin D. MacLeod wrote: >> >> Hi All, >> >> I'm a fairly experienced GIS user, but I'm new to QGIS. I'm using version >> 2.2, and I'm trying to convert a point data layer into a raster data layer >> using the Rasterize tool. The point data layer has an integer field with a >> value of 1 for all records, and I want to make a raster data layer which >> has a value of one for each cell which has at least one point in it (some >> cells have more than one point in them). When I use the Rasterize tool, it >> creates the raster data layer fine, but all cells with have points in them >> appear to have a value of 0.995968. I've tried editing the gdal code (even >> making the resulting raster data layer an integer layer), but I still >> cannot get it to produce a raster with a value of 1 rather than just a >> number very close to one. >> >> Does anyone have any suggestions of where I might be going wrong and/or >> how to solve this issue? >> >> On a related note, is it possible to use the Rasterize tool to work out >> the average or total values for all the points which fall in each grid >> cell? If so, how (I can't find anything in the gdal instructions themselves >> which would suggest this is possible, but I might be missing something). If >> this isn't possible to do with the Rasterize tool, are there other tools in >> QGIS which can do this? >> >> Thanks for any help anyone can give on this. >> >> All the best, >> >> Colin >> >> >> ================================================================================== >> GIS IN ECOLOGY - Providing Training, Advice And Consultancy On The Use Of >> GIS In Ecology >> >> Web: www.GISinEcology.com Email: [email protected] >> >> Need to ask a question about using GIS? Try the GIS In Ecology Forum: >> www.GISinEcology.com/GIS_in_Ecology_forum.htm >> >> Books From GIS In Ecology Staff: >> >> An Introduction To Using GIS In Marine Biology; RRP: £44.99 >> An Introduction To Using GIS In Marine Biology: Supplementary Workbook >> One - Creating Maps Of Species Distribution; RRP: £19:99 >> An Introduction To Using GIS In Marine Biology: Supplementary Workbook >> Two - Working With Raster Data Layers; RRP: £19.99 >> >> If you wish to purchase these books, visit: >> http://www.gisinecology.com/Book_Shop.htm >> >> To help the environment, please do not print out this email unless it is >> unavoidable. >> >> ================================================================================== >> >> >> This mail was received via Mail-SeCure System. >> >> >> _______________________________________________ >> Qgis-user mailing >> [email protected]http://lists.osgeo.org/mailman/listinfo/qgis-user >> This mail was received via Mail-SeCure System. >> >> >> >> >> >> _______________________________________________ >> Qgis-user mailing list >> [email protected] >> http://lists.osgeo.org/mailman/listinfo/qgis-user >> > > > ------------------------------ > _______________________________________________ > Qgis-user mailing list > [email protected] > http://lists.osgeo.org/mailman/listinfo/qgis-user > > > _______________________________________________ > Qgis-user mailing list > [email protected] > http://lists.osgeo.org/mailman/listinfo/qgis-user >
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