[gdal-dev] Help with color map for raster grid

[Chaitanya kumar CH]

Daniel,

You can build your own colour table using the api. In not familiar with the
C# interface but for C, you can refer to
http://gdal.org/classGDALColorTable.html

--
Best regards,
Chaitanya Kumar CH
On 25-Feb-2014 8:58 pm, "windchaser" <dkaminski at gmail.com> wrote:

> Chaitanya,
>
> Thanks for your prompt reply. I think I would like to use display engine,
> but I am still trying to figure out which function I need to use to 'load a
> different color table'. I am using GDAL with C# in a VS2010 project. Below
> is the function that opens the raster text file and returns the bitmap.
>
> when trying to retrieve the color table using this statement "ColorTable
> ct = band.GetRasterColorTable();" the color table returned is empty.
>
> From your post I understand that a VRT dataset needs to be created by
> copying the source dataset and then this VRT dataset can be manipulated to
> add more classes apply a color gradient to the classes.
>
> Are there any C# examples of using VRT dataset?
> Could you highlight the main steps that I need to take in order to achieve
> this?
>
> Thanks,
>
>     public static Bitmap GetBitmap(string sFileName)
>     {
>         //**How to write manipulated raster values to ASCII grid with GDAL?
>         //**
> http://stackoverflow.com/questions/10635107/how-to-write-manipulated-raster-values-to-ascii-grid-with-gdal
>         OSGeo.GDAL.Dataset ds = Gdal.Open(sFileName,
> OSGeo.GDAL.Access.GA_ReadOnly);
>         if (ds == null)
>         {
>             MessageBox.Show("Invalid File Format!");
>             return null;
>         }
>
>         OSGeo.GDAL.Driver dr = ds.GetDriver();
>
>         int nWidth = ds.RasterXSize;
>         int nHeight = ds.RasterYSize;
>
>         //** GDAL CSharp Guide gdal - Revision 26980:
> /trunk/gdal/swig/csharp/apps
>         //** http://svn.osgeo.org/gdal/trunk/gdal/swig/csharp/apps/
>
>         // Creating a Bitmap to store the GDAL image in
>         Bitmap bitmap = new Bitmap(nWidth, nHeight,
> PixelFormat.Format8bppIndexed);
>         // Obtaining the bitmap buffer
>         BitmapData bitmapData = bitmap.LockBits(new Rectangle(0, 0,
> nWidth, nHeight), ImageLockMode.ReadWrite, PixelFormat.Format8bppIndexed);
>         try
>         {
>             int stride = bitmapData.Stride;
>             IntPtr buf = bitmapData.Scan0;
>             Band band = ds.GetRasterBand(1);
>             band.ReadRaster(0, 0, nWidth, nHeight, buf, nWidth, nHeight,
> DataType.GDT_Byte, 1, stride);
>         }
>         finally
>         {
>             bitmap.UnlockBits(bitmapData);
>         }
>
>         return bitmap;
>     }
>
>
>
> *Daniel*
> c: 1 (705) 499-2450
>
>
> On Tue, Feb 25, 2014 at 12:01 AM, chaitanya_ch [via OSGeo.org] <[hidden
> email] <http://user/SendEmail.jtp?type=node&node=5105844&i=0>> wrote:
>
>> Daniel,
>>
>> You can make changes in two places. In the data or the display engine. In
>> the data, you can modify the colour table. This will be permanent. In the
>> display, you just load a different color table based on the table of pixel
>> values. If you don't like either, you can build a gdal vrt file and modify
>> its colour table.
>>
>> http://www.gdal.org/gdalbuildvrt.html
>> http://www.gdal.org/gdal_vrttut.html
>>
>> --
>> Best regards,
>> Chaitanya Kumar CH
>> On 25-Feb-2014 9:26 am, "windchaser" <[hidden email]<http://user/SendEmail.jtp?type=node&node=5105703&i=0>>
>> wrote:
>>
>>> Hi,
>>> I am working with GDAL in a C# project. I need help figuring out how to
>>> increase the colors displayed on a raster grid. Opening the file using
>>> Gdal.Open("myfile", OSGeo.GDAL.Access.GA_ReadOnly); seems to offer some
>>> colors but I would like to increase the number of colors for the raster
>>> map,
>>> specially for floating point raster.
>>>
>>> Here is an example of what i am trying to achieve using GDAL.
>>>
>>> http://screencast.com/t/LPjJ7pTk <http://screencast.com/t/LPjJ7pTk>
>>>
>>> Thanks for your help!
>>>
>>> Daniel
>>>
>>>
>>>
>>> --
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