[Qgis-user] Problem with Rasterize (Vector to raster) tool

Fri Apr 11 03:30:49 PDT 2014

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 <
cdmacleod at gisinecology.com> 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: info at GISinEcology.com
>
> 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 <sig.upagu at gmail.com>
> *Sent:* Thursday, April 10, 2014 9:23 PM
> *To:* qgis-user at lists.osgeo.org
> *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 <micha at arava.co.il>:
>
>>  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: info at GISinEcology.com
>>
>> 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 listQgis-user at lists.osgeo.orghttp://lists.osgeo.org/mailman/listinfo/qgis-user
>> This mail was received via Mail-SeCure System.
>>
>>
>>
>>
>>
>> _______________________________________________
>> Qgis-user mailing list
>> Qgis-user at lists.osgeo.org
>> http://lists.osgeo.org/mailman/listinfo/qgis-user
>>
>
>
> ------------------------------
> _______________________________________________
> Qgis-user mailing list
> Qgis-user at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/qgis-user
>
>
> _______________________________________________
> Qgis-user mailing list
> Qgis-user at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/qgis-user
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/qgis-user/attachments/20140411/7585fc5f/attachment.html>