Wednesday, May 17, 2017

Code snippet: Identify to which polygon a point belong to?

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Code sample to find point inside a polygon in shape file using GDAL/OGR 2.x and C#.

using OSGeo.OGR;
using OSGeo.OSR;
using OSGeo.GDAL;
1:  public void FindPolygonBelongsToPoint()   
2:      {  
3:        try   
4:        {  
5:          var shapePath = @"C:\Locations_WGS84.shp";  
6:          Ogr.RegisterAll();  
7:          OSGeo.OGR.Driver shapeDriver = Ogr.GetDriverByName("ESRI Shapefile");  
8:          DataSource shape = shapeDriver.Open(shapePath, 0);  
9:          Layer layer = shape.GetLayerByIndex(0);  
11:          Feature polygonFeature = layer.GetNextFeature();  
13:          long featureCountInLayer = layer.GetFeatureCount(1);  
14:          for (int i = 1; i <= featureCountInLayer; i++) {  
16:            Geometry polygonGeom = polygonFeature.GetGeometryRef();  
18:            string coordinates = "POINT (-100.726 38.995)";  
20:            SpatialReference spatialRef = layer.GetSpatialRef();  
21:            Geometry point = Ogr.CreateGeometryFromWkt(ref coordinates, spatialRef);  
23:            bool isInside = point.Within(polygonGeom);  
25:            if (isInside)  
26:            {  
27:              var val = polygonFeature.GetFieldAsString(4);  
28:              Console.WriteLine("Found one");  
29:            }  
31:            polygonFeature = layer.GetNextFeature();            
32:          }         
34:        }  
35:        catch (Exception ex)   
36:        {  
38:          Console.WriteLine(ex.Message);  
39:        }          
41:      }  

Thursday, January 19, 2017

Code snippet : Create/update polygon attribute fields using Ogr and ESRI Arcobjects

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A code snippet example to check if a feature is standalone ESRI Shape or featureclass inside ESRI Gdb, then add new filed or update attribute value in attribute table .... standalone shape/features are created/updated using GDAL/OGR implementation and feature/featureclass stored in ESRI personal GDB are created/updated using ESRI ArcObjects.  Any solution to replace later with GDAL/Ogr is highly appreciated.  Please comment below if you find one.

 public void AddUpdateAttributeField(string oldFeatureFile)  
       DataSource dataSource;  
       Layer layer;  
       var isShapeFile = IsShapeInGdb(oldFeatureFile);  
       if (isShapeFile)  
         dataSource = Ogr.Open(oldFeatureFile, 1); //second argument in open specifies mode of data, 1 RW & 0 readonly mode  
         layer = dataSource.GetLayerByIndex(0);  
         FieldDefn gdalFiedlDefn = new FieldDefn("FID_GDAL",FieldType.OFTInteger);  
         layer.CreateField(gdalFiedlDefn, 0);  
         Feature feature = layer.GetNextFeature();  
         while (feature!= null)  
           feature.SetField("FID_GDAL",feature.GetFID()); // Add FID shapefile  
           feature = layer.GetNextFeature();  
           string gdbPath = Path.GetDirectoryName(oldFeatureFile);  
           string featureName = Path.GetFileNameWithoutExtension(oldFeatureFile);  
           IWorkspaceFactory workspaceFactory = new FileGDBWorkspaceFactory();  
           IFeatureWorkspace featureWorkspace = (IFeatureWorkspace)workspaceFactory.OpenFromFile(gdbPath, 1);  
           IFeatureClass featureClass = featureWorkspace.OpenFeatureClass(featureName);  
           IFields fields = featureClass.Fields;  
           if (fields.FindField("FID_GDAL") == -1)  
             // Create a Int field called "FID_GDAL" for the fields collection

Friday, January 13, 2017

Code snippet: Create new Field in a Shape File using GDAL/OGR in C#

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Add new field in existing shape file using OGR in C#.
 public void AddAttributeField(string oldShapeFile)  
       DataSource dataSource = Ogr.Open(oldShapeFile, 1); //second argument in open specifies mode of data, 1 RW & 0 readonly mode  
       Layer layer = dataSource.GetLayerByIndex(0);  
       FieldDefn gdalFiedlDefn = new FieldDefn("NEW_FIELD",FieldType.OFTInteger);  
       layer.CreateField(gdalFiedlDefn, 1);  
       Feature feature = layer.GetNextFeature();  
       while (feature!= null)  
         feature.SetField("NEW_FIELD",feature.GetFID()); // Populate new field with feature FID  
         feature = layer.GetNextFeature();  

Wednesday, October 14, 2015

Read ESRI File Gdodatabase (FileGDB) using GDAL & C#

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If you are creating a new project- set up GDAL & C# environment as described here

Code snippet to read ESRI File Geo-database (FileGDB) using GDAL and C#. By default it uses GDAL's 'OpenFileGDB' (read only) driver with out any external dependencies. If you are interested in editing GDB feature class you should use 'FileGDB' (read-write) driver, which had dependency on ESRI's FGDB API SDK. The UCLA's internal testing showed that ESRI's FileGDB driver drags the performance than OpenFileGDB for read-only operation. So choose the driver according to your needs.

However, both GDAL drivers and ESRI's API do not support the raster dataset inside the GDB till date.

 public static void ReadEsriGdb(string gdbPath, string featureLayerName)  
       //Register the vector drivers  
       //Reading the vector data  
       DataSource dataSource = Ogr.Open(gdbPath, 0);  
       Layer layer = dataSource.GetLayerByName(featureLayerName);  
      ReadEsriGdb("gdbPath.gdb", "counties");  

Tuesday, September 22, 2015

Read raster block by block or row by row using GDAL and C#

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If you are creating a new project- set up GDAL & C# environment as described here

Code Snippet: Read raster block by block using GDAL and C#
 private static void ReadRasterBlocks(ref Dataset valueRaster)  
   Band bandValueRaster = valueRaster.GetRasterBand(1);  
   int rasterRows = valueRaster.RasterYSize;  
   int rasterCols = valueRaster.RasterXSize;  
   const int blockSize = 1024;  
   for(int row=0; row<rasterRows; row += blockSize)  
      int rowProcess;  
      if(row + blockSize < rasterRows)  
        rowProcess = blockSize;  
        rowProcess = rasterRows - row;  

Wednesday, September 16, 2015

Read a raster file into an Array using C# and GDAL

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If you are creating a new project- set up GDAL & C# environment as described here

Code snippet: Read raster into an Array using GDAL and C#

 //Register all drivers  
 //Read dataset  
 Dataset rasterDataset = Gdal.Open("rasterName.tif", Access.GA_ReadOnly);  
 if (rasterDataset == null)  
      Console.WriteLine("Unable to read input raster..");  
 //raster bands  
 int bandCount = rasterDataset.RasterCount;  
 if (bandCount > 1)  
      Console.WriteLine("Input error, please provide single band raster image only..");  

Tuesday, September 15, 2015

Clip a raster with shapefile using C# and Gdal

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Over the week, I stumbled on problem clipping raster with feature using C# and Gdal and come up with following solution, which clips the features and fills no data value for missing raster  values inside the extent. If you are creating a new project- set up GDAL & C# environment as described here

Friday, September 11, 2015

Vector to Raster Conversion using GDAL & C#

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I have been working on a .Net based project that requires feature to raster conversion without using ESRI ArcObjects. The GDAL seem's an obvious solution to us and wrote a small snippet for rasterize layer using Gdal and C#. Hope it will help someone someday...

Step 1: Setup the environmental variables for GDAL 
(Copied here for future reference - )

The Geospatial Data Abstraction Library (GDAL) is great if you want to process raster data, especially regarding format conversion. I want to use GDAL for a biodiversity modelling project, so I had a look at the C#-bindings of GDAL. The described steps work both with VS 2010 as well as VS 2012, what you need to do is:
  • Download the latest version of the precompiled GDAL binaries from here. Choose the ones that suit your system (32bit or 64bit). Extract the contents from the zip file to a location on your hard disk e.g. C:\Program Files\GDAL (I ran into a number of AccessViolationExceptions when I used the binaries from FWTools 2.4.7).
  • Include both the path to C:\Program Files\GDAL\bin\gdal\csharp as well as C:\Program Files\GDAL\bin in your PATH system variable.
Setting of the PATH variable
Creating a Console Application (VS 2010)
  • Add four of.the dll-files that can can be found at C:\Program Files\GDAL\bin\gdal\csharp (or wherever your installation path of the current binaries is) to your project references: gdal_csharp.dllgdalconst_csharp.dllogr_csharp.dll and osr_csharp.
Adding necessary references (VS 2010)
  • Build the solution. If you are on a 64bit system and you are using the 64bit GDAL binaries you have to make sure you actually build for 64bit (you will get errors otherwise when you try to run the program).
Setting of the platform target for 64bit (VS 2012)
  • Now you can run the program with some data. Include a reference to one of the raster files in the Command line arguments field of your Debug options (in the properties of your GDALInfo project; don't forget to put the path inside double quotes of it includes blanks).
  • Run the program (Ctrl-F5). It should show you something similar to the following:
Output of GDALInfo
That's it. Now you can use the other example C#-programs to open, copy, manipulate raster data in variety of file formats. For some of the other example files it is necessary to add some additional references (e.g. System.Drawing).
(End copy)

Step 2: Open visual studio and create C# console project

Import references 
  • gdal_csharp
  • gdalconst_csharp
  • ogr_csharp
  • osr_csharp
Import Namespaces

using OSGeo.GDAL;
using OSGeo.OGR;
using OSGeo.OSR;

Friday, May 15, 2015

Tiler tools, an alternative scripts to for creating raster tiles from digital maps

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Other day I was working to generate the Google Map based raster tiles using Gdal2tiles for a large raster file, 30GB in size. Gdal2tiels complains about the following error, which I had no clue.

Then fiddling with others tilers available I played with the Tilers-tools, python Scripts for raster tile sets from digital maps with GDAL dependency. After spending few days hit and trial, finally I am able to generate raster tiles compatible with Google Maps. Here I am sharing the steps that I follow to produce tiles using the Tiler tool. Hope it will help some of the OSGeo users. I have divided tile generation steps into two groups, dependency installation and data preparation with a presumption that you are already familiar with GDAL.


STEP 1. Install Python geospatial packages

Install the dependencies as described-

For my project, I used 32 bit installers and Python 2.7. Strictly follow the python Geospatial package dependency installation orders and do not mix the 64 bit and 32 bit dependencies

STEP 2. Install the Tiler tools

Download and unzip the Tiler tool from:

STEP 3. Set Python and Gdal path in Tiler’s bat file

Open : tilers-tools.bat from unzipped Tiler tool
         set PYTHON=C:\Python27 ( As you assigned the path in Step 1)
         set GDAL=C:\Program Files (x86)\GDAL ( As you assigned the path in Step 1)

STEP 4. Environmental variable setting on your machine

Set GDAL_DATA & path in your environmental variable setting.

                   Variable          Value

       GDAL_DATA = C:\Program Files (x86)\GDAL\gdal-data

        path = C:\Program Files (x86)\GDAL

Wednesday, May 25, 2011

Raster Misalignment with Base Data in ArcMap10

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In the early Friday morning of mid May, I got an email from one of my team member about raster misalignment problem in ArcGIS10. I also tried to overlay couples of previously working Tiff and Grid raster files in ArcMap9.3 and ArcMap10. The ArcMap9.3 overlay raster files perfectly aligned as we all desired, but ArcMap10 did not.


From the ESRI website, I got to know that the issue of misalignment of Tiff in ArcMap10 is a bug in ArcGIS 10. The ESRI team announced two solutions to solve Tiff shift into wrong geographic locations:


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