ASP.NET xDomainProxy for OpenLayers getInfo requests

After a long time of just talking about using geoserver we have eventually installed it on our server. Making it work behind IIS is a subject for another article and I am hoping to post it soon.

Anyway, we decided to make our geoserver available at, while the applications we write are likely to be hosted under different subdomains or even under different domains. Since x-domain requests are not allowed in JavaScript due to some security restrictions I needed to create a simple server side proxy that would be exposed to application as a local resource and would take care of pulling the info when a getInfo requests are issued by OpenLayers.

I started with setting up a proxyHost in OpenLayers:

//proxy host
OpenLayers.ProxyHost = 'xDomainProxy.ashx?url=';

Then a server side script for a generic handler:

<%@ WebHandler Language="C#" Class="xDomainProxy" %>

using System;
using System.Web;

public class xDomainProxy : IHttpHandler {
    public void ProcessRequest (HttpContext context) {

        //OpenLayers.ProxyHost = 'xdomainProxy.aspx?url=' so the requested url is passed in a url param
        string requestUrl = HttpUtility.UrlDecode(context.Request.QueryString["url"]);

        //test if the request string was passed and of so request data from the destination server
        if (requestUrl != null)
            //create a new HttpWebRequest
            System.Net.HttpWebRequest webRequest;
            webRequest = (System.Net.HttpWebRequest)System.Net.HttpWebRequest.Create(requestUrl);
            webRequest.Method = "GET";

            System.Net.HttpWebResponse response = (System.Net.HttpWebResponse)webRequest.GetResponse();

            //check if the data was successfully retrieved
            if (response.StatusCode.ToString().ToLower() == "ok")
                //set the appropriate response content type
                context.Response.ContentType = response.ContentType;

                //Read the stream associated with the response.
                System.IO.StreamReader reader = new System.IO.StreamReader(response.GetResponseStream());

                //and write it to response
    public bool IsReusable {
        get {
            return false;

And voila, it's ready to be used ;)

A side note: although in many cases this proxy will work properly this is a mini version of the code and should not be implemented in the production environment - it does not catch any errors and will fail if the connection is not available. Also it was written to work with OpenLayers specifically (OpenLayers.ProxyHost) and needs some extra work before it can act as a bit more flexible proxy allowing one to pull data without having to escape the passed url.

A generic error occurred in GDI+

Recently I have been working on a tile serving utility that would generate tiles on the fly but also cache them at the same time for future usage. After releasing our map tiling tool for manifold this was the next step.

The tile rendering functions were working nicely and the process was fairly quick so enabling data caching functionality could only speed things up ;-) So far so good... It was supposed to be just a matter of saving the output bitmap to a file... So I did it the way I usually do and tried to save my tile this way:

mapImageBitmap.Save(path, _outputTileFormat);

 Apparently this was throwing an error. A very descriptive one: A generic error occurred in GDI+... Not very helpful, is it?

After googling for a while it looked like this was supposed to be a permissions problem but allowing my IUSR to write to the specified folder did not help at all. What's worse I have found some info on the msdn that one should avoid using the System.Drawing namespace in ASP.NET: Classes within the System.Drawing namespace are not supported for use within a Windows or ASP.NET service. Attempting to use these classes from within one of these application types may produce unexpected problems, such as diminished service performance and run-time exceptions.

Nice huh?

Another solution I found on the web was to clone the bitmap in question and then save it, though that gave the same error. No avail in my case.

Luckily after messing with the problem a bit more I have discovered that writing a bitmap to a memory stream and then saving the data using Sytem.IO.File.WriteAllBytes did the trick:

System.IO.MemoryStream outStream = new System.IO.MemoryStream();
mapImageBitmap.Save(outStream, _outputTileFormat);
System.IO.File.WriteAllBytes(_requestedTilePath, outStream.ToArray());

Defitions of Polish projections for manifold

With version 8.0.19 manifold team added some of the Polish projections to manifold projection presets. Basically they added five zones of the National Coordinate System 1965 (PUWG 1965, zones I, II, III, IV and V). There seems to be a mistake though with the way they named the projections: National Coordinate System 1965 was named 1942 while the only one that has 5 zones for Poland is 1965.

For those interested in using Polish coordinate systems with manifold attached is a custom projection xml (it will display in a folder Poland_Custom in the assign / change projection dialog). This is the best we came up with so far so please bear in mind that it may not be 100% perfect. For some more details please see a discussion at

Styling Navteq data using Manifold

Recently we were asked to prepare some map layers for a web application. The exercise was about styling Navteq 2010 data in manifold so created maps can be then used for rendering a tiled base map but also used by a map server.

Although manifold lacks some of the carto tools available in other GIS packages or graphic software it does offer enough to complete such task. It actually does offer some other functions that let one create some nice map features - for example the road shields labels were created from a drawing linked to a SQL query that created road label points spaced evenly along the road lines. This backed with the automatic resolution of label conflicts allowed us to nicely place the road shields on the map.

Cutting image from a bigger raster source

This script has already been posted on the ( so nothing new will be presented...

There was one interesting thing though - how to get from a bbox of a geom used by the input drawing to the actual size of the output image in pixels. The script needed to cut images and preserve their actual resolution - as one would crop an image in photoshop.

First I had to prepare a coordinate converter and to grab some data off the image coordinate system needed later for calculating the actual size of a cut image in pixels:

//prepare coordinate converter in order to properly calculate image extent in pixels later
Manifold.Interop.CoordinateConverter coordConverter = manApp.NewCoordinateConverter();
coordConverter.Prepare((Manifold.Interop.Base)map.CoordinateSystem, (Manifold.Interop.Base)inputImage.CoordinateSystem);

//also grab the input image local scales
double imageLocalScaleX = inputImage.CoordinateSystem.ParameterSet["localScaleX"].Value;
double imageLocalScaleY = inputImage.CoordinateSystem.ParameterSet["localScaleY"].Value;

The next step was to grab the bounding box of a source geometry used to cut a new image from the source raster:

//grab the bounding box of an object
Manifold.Interop.Rect geomBbox = geomSet.get_Item(n).Box;

After that I used the bottom left and top right corners of the bbox and coverted them to the source image coordsys in order to calculate the size of the new image in pixels:

//get the corner points of the geom's bbox
Manifold.Interop.Point bottomLeft = manApp.NewPoint(geomBbox.XMin, geomBbox.YMin);
Manifold.Interop.Point topRight = manApp.NewPoint(geomBbox.XMax, geomBbox.YMax);

//convert them to the image coordsys
coordConverter.Convert((Manifold.Interop.Base)bottomLeft, null);
coordConverter.Convert((Manifold.Interop.Base)topRight, null);

//image size in pixels
int imageSizeX = (int)((topRight.X - bottomLeft.X) / imageLocalScaleX);
int imageSizeY = (int)((topRight.Y - bottomLeft.Y) / imageLocalScaleY);

//and then cut tile
map.RenderAreaTo(fileName, imageSizeX, imageSizeY, geomBbox, true);

Fairly straight forward isn't it?

Anyway, if you would like to use this script it is attached below. There are some input params and they need to be set prior to running the script. The reason behind using a RenderAreaTo method of a map object instead of the image object is explained in the script.

Although perhaps it would be easier to use gdal for the task than writing a script this exercise seemed to be interesting enough to give it a go. Having a GUI environment to choose areas of interest by simply drawing a rectangle over the image is a good reason isn't it ;-) Make sure though you switch off the input drawing before rendering the new images...

Also bear in mind that if you work with a high resolution ecw for example, the image you want to cut may be quite large since and the script calculates its size based on the source image resolution - to make it simpler: trying to cut a too big image out of a high res source image may make your pc unresponsive for a longer time ;-)

EDIT: I would almost forget - the input drawing is expected to have a column with names for the new images.

tileCutter.cs (7.53 kb)