[Gvsig_english] Create Slope from Contour Line

Wed Jul 13 09:35:07 CEST 2011

Dear Simon,

It could work with cell 250, since I am using 50 meter data and it's quite
detail data, so I work with cell 250 and it could run well.
But unfortunately, at the Step 5, i was confused, When the dialog
"Unsupervised classification (clustering) appeared, there's Band, what
should I choose? 1 element (from slope)? the result was onlie one single new
file with single color. I don't know what when wrong from the process i've
been through. Then, when I did "Vectorize raster layer (polygons), there's
appear a new file and i can look the table, but i couldn't see the vector
layer. I didn't know what've been missing.

Could you help solve the problem?

Looking forward for your assistance. Thanks so much.

Regards,

Adi

**

On 11 July 2011 12:52, Simon Cropper <scropper at botanicusaustralia.com.au>wrote:

> Adi,
>
> If you can see the contours and pan then the program should be working.
>
> My gut feeling is that your dataset may be too big.
>
> Use the geotools to cut a section out of the contour dataset that is
> substantially smaller (e.g. 1000mx1000m). If this works then it is
> merely a matter of waiting until the task is completed. If this small
> dataset does not work then there is a more fundamental issue (although
> when this happens errors pop up everywhere).
>
> Also remember that although the laptop has 4GB, it is what the Java VM
> is set to that counts. You may not have much memory set aside for java
> to do its work. If you check the text file C:\Program
> Files\gvSIG_1.10\bin\gvSIG.ini, you will see the text "-Xmx500M"
> somewhere near the top of the file. If the value is less than 500 then
> you should be able to increase it then restart gvSIG and start again.
>
> On 11/07/11 14:54, Adi Fajar RAMLY wrote:
> > Dear Simon,
> >
> > I don't know what is wrong with my laptop, or should I use PC to work
> with
> > gvSIG?
> > Everytime I want to Rasterize Vector Layer, the process indicator didn't
> > even move. It couldn't work at all.
> > I don't know why?
> >
> > By the way, this is the Spec of my Toshiba Qosmio:
> > System: Rating 5.6 windows experience index
> > PRocessor: Intel(R)Core(TM) i3 CPU M350  @2,27 GHz 2,27
> > RAM: 4.00GB (2.98 GB usable)
> > System Type: 32-bit Operation System
> >
> > I haven't tried work with PC. Looking forward.
> >
> > Regards,
> >
> > Adi
> >
> > -------------------
> >> Adi,
> >>
> >> Here is a draft tutorial I have in the mill to publish on my website.
> >>
> >> I am willing to release the text here under a Creative
> >> Commons-Attribution-ShareAlike (CC-BY-SA Australia 3.0) licence, as the
> >> process was thrashed out with the help of all the great people on this
> >> list.
> >>
> >> http://creativecommons.org/licenses/by-sa/3.0/au/deed.en
> >>
> >> Eventually I will be releasing the tutorial using actual data and images
> >> showing each step, so if you are interested you can put yourself on the
> >> email notification list.
> >>
> >> If you have any problem following the steps in the following tutorial
> >> let me know and I will see if I can help you through the issues.
> >>
> >> **Terrain analysis using contour data**
> >>
> >> *Step 1. Preparation*
> >>
> >> Open a project file, create a new view and add your contour data file to
> >> the view. This shapefile should contain a numeric field indicating the
> >> elevation or altitude.
> >>
> >> *Step 2. Create a DEM*
> >>
> >> Open Sextante and choose “Rasterize Vector Layer” under the
> >> “Rasterization and interpolation” category.
> >>
> >> You should see the 'Rasterize Vector Layer” Dialog.
> >>
> >> Choose the vector layer and elevation/altitude field, and input a
> >> legitimate output file name.
> >>
> >> In the Raster Output Tab, select 'Use Extent from layer” and under cell
> >> size input 20, 50 or 100m for the size of the cell. You will need to
> >> experiment with this value to obtain the best output.
> >>
> >> You should end up with a black box with white cells overlapping the
> >> contour positions. The black areas are voids in the grid file and do not
> >> contain data. This file is referred to as a Digital Terrain Model or
> DEM.
> >>
> >> *Step 3. Filling in the blanks*
> >>
> >> The next step is to fill in the values between the grid cells that
> >> appear in the DEM.
> >>
> >> Open Sextante and choose “Void Filling” under the “Basic Tools for
> >> raster layers” category. The “Void Filling” dialog should appear.
> >>
> >> Choose the raster layer, and input a legitimate output file name. Leave
> >> the Tension threshold at 0.1.
> >>
> >> You should end up with a graduated black-and-white raster file.
> >>
> >> If you move your contour file above the raster file in your Table of
> >> contents, you can visually confirm that the elevation matches the raster
> >> file created.
> >>
> >> Right click the raster file and select “Raster Properties” then open the
> >> “Bands” tab. Check and uncheck R, G, B radio buttons to see how the map
> >> changes. Although not part of the analysis it helps if your choose a
> >> colour you find appealing and contrasts well with your contours.
> >>
> >> Right click the raster file and select “rename” and allocate a name that
> >> makes sense (e.g. rast_void_filling) to distinguish the raster from
> >> others versions.
> >> Step 4. Clean up the DEM
> >>
> >> Open Sextante and choose “Crop grid with polygon layer” under the “basic
> >> tools for raster layers” category.
> >>
> >> *Step 4. Establishing the Slope*
> >>
> >> Open Sextante and choose “Slope” under the “Geomorphometry and terrain
> >> analysis” category. The “Slope” dialog should appear.
> >>
> >> Select complete raster file (e.g. rast_void_filling), the type of slope
> >> and units required (in my case I use 'Maximum slope Travis et al.1975'),
> >>   and a legitimate name for the output file.
> >>
> >> In the “raster output” tab select “Use extent from layer” and select the
> >> raster file being used (e.g. rast_void_filling) and leave the cell size
> >> the same (i.e. 20m).
> >>
> >> You should have a black screen with faint lighter areas where slope are
> >> greater. Depending on the variation across the site then this raster
> >> file can be difficult to visualize. Move your contour file above the
> >> raster in the ToC and use the information tools to query individual
> >> cells to see if the results are as expected. You can play with the
> >> values in the enhance tab to try and visualize the changes in the cell
> >> values.
> >>
> >> *Step 5. Create classification groups for slope*
> >>
> >> Open Sextante and choose “Unsupervised classification (clustering)”
> >> under the “Raster layer analysis” category. The “Unsupervised
> >> classification (clustering)” dialog should appear.
> >>
> >> Select Raster Layer, set the number of classes to 5 and define a
> >> legitimate raster file name and database name. The database will contain
> >> the boundary of the classes.
> >>
> >> Open Sextante and choose “Vectorize raster layer (polygons)” under the
> >> “Vectorization” category. The “Unsupervised classification (clustering)”
> >> dialog should appear. Select the raster and a legitimate name.
> >>
> >>
> >> I hope this helps.
> >>
> >> --
> >> Cheers Simon
> >>
> >>     Simon Cropper
> >>     Website Administrator
> >>     http://gis.fossworkflowguides.com
> >>     The fosGIS Workflow Guide
> >>
> >>     * English - detected
> >>     * English
> >>
> >>     * English
> >>
> >>   <javascript:void(0);>  <#>
> >> _______________________________________________
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> >>
> >
> >
> >
>
>
> --
> Cheers Simon
>
>    Simon Cropper
>    Principal Consultant
>    Botanicus Australia Pty Ltd
>    PO Box 160, Sunshine, VIC
>    W: www.botanicusaustralia.com.au
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>

-- 
Adi Fajar Ramly
GIS Division
Ministry of Environment
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