[Gvsig_english] Create Slope from Contour Line

Mon Jul 11 07:52:17 CEST 2011

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