First day at ESRI

I just had my first day at ESRI today, where I have joined the ArcGIS Server .NET ADF team.

Everything here seemed well-prepared and set-up when I got there, including a small "seminar" for everyone who started as ESRI today, and ready-installed desktop and laptop computers.

I already got to look "under the hood" of AGS and play around with it - there's definitely some very cool stuff in there! Hopefully I'll get some time to blog some more about it later - or you can have a look at Arts blog as well.

Up-to-date maps

Yesterday I went on my very first "road-trip" in USA, driving from Redlands up to San Luis Obispo to visit a friend of mine, a 5-6 hours drive. Of course I brought my TomTom  navigator to help out (since I had more or less no idea how to get up there), and already after 10 miles of driving it got handy, when the whole I-10 freeway closed, probably because of yet another accident. TomTom has a neat little feature to avoid roadblocks or entire parts of the trip, and provide you with an alternative.

I wasn’t  too sure how up-to-date the map was, but thought I would let it guide me on a round trip. Well it turned out that the maps were a little too up-to-date, when it suddenly wanted me to enter an only half  completed freeway :-). Good thing I brought my paper-maps as well, although they are far harder to use while driving ;-)

Overlaying Local Live maps with your own map-data

Recently the Virtual Earth team  released a new version of their API . One of the new features allowed to overlay the maps with tiles from your own tile-server. The tile-server can be added using a few lines of javascript like this:

var tileSourceSpec = new VETileSourceSpecification();
tileSourceSpec.ID = "POPDENS" ;
tileSourceSpec.GetTilePath = GetTilePath;
tileSourceSpec.NumServers = 1;
tileSourceSpec.MinZoom = 1;
tileSourceSpec.MaxZoom = 16;
var tileLayer = new VELayerSpecification(VELayerType.VETileSource,"POPDENS", "POPDENS");

This will add a new tile layer named "POPDENS" to the virtual earth map, and make it slightly transparent. The GetTilePath parameter refers to the JavaScript method that creates the request-url to the server. Ex:

function GetTilePath (tileContext)  {
  if (tileContext != null && tileContext != "undefined" ) {
    return "VEmap.ashx?WIDTH=256&HEIGHT=256&X=" + tileContext.XPos + "&Y=" + tileContext.YPos + "&ZoomLevel=" + tileContext.ZoomLevel;

The X, Y and ZoomLevel parameters in this querystring are unfortunately not simple coordinates, but are the row/column of the tile at the current zoom level. Rob Blackwell has earlier posted an article on how to convert these to longitude/latitude values.

The next step is to create the tile-server. I used SharpMap for this. SharpMap's on-the-fly transformation capability is needed to transform the data to the Mercator projection that Virtual Earth uses, but any map-renderer that can project data could be used. You could also create a javascript that makes the GetTilePath method return a WMS request instead and then use any of the many WMS servers available.

The basic trick is to use Rob Blackwell's methods for calculating the longitude/latitude of each tile's corners, transform these coordinates to the Mercator projection and render the resulting extent.

You can view a small demo of a Population Density map overlaying the Virtual Earth map here:
...or you can download the full source: (389,09 KB)
You can easily add your own data by editing the CreateMap method in \App_Code\Map.cs


SharpMap v0.9 released

SharpMap v0.9 is now uploaded to the CodePlex Workspace.

Download it here.

Thanks to everyone who has supported the development of SharpMap. We have come a long way since the previous release candidate.

Unfortunately this also marks the end of my involvement with SharpMap. In a months time I'm moving from Copenhagen to California to start on a new and exciting GIS developer job. Hopefully more on that later...

Microsoft SQL Server Spatial project

Inspired by my petty shot at making SQL Server spatial, Ricardo Stuven has been working the new CLR in SQL Server 2005 and started adding almost all basic spatial functions, and implemented some aggregates, stored procedures and table-valued functions in SQL Server. He even started an Open Source project where you can check it out (yet another open source .NET GIS project we can add to the .NET tribe... ;-))

Read his comments on his approach, including query examples and a list of features which he posted in an update on the SharpMap forum today.

Open Source GIS can only be made using either C and Java...

...well at least according to this "white" paper from Refractions. Quote:

Open Source GIS software can be categorized into two largely independent development tribes. [...]

  • The ‘C’ tribe, consisting of developers working on UMN Mapserver, GRASS, GDAL/OGR, OSSIM, Proj4, GEOS, PostGIS, QGIS, MapGuide OS and OpenEV. The ‘C’ tribe also includes users of scripting languages that bind easily to C libraries, such as Python, Perl and PHP.
  • The ‘Java’ tribe, consisting of developers working on GeoTools, uDig, GeoServer, JTS, JUMP, and DeeGree.

Don't get me wrong - I think the above libraries are GREAT (I use many of them daily) but I think this is a strange way of categorizing software. First of all what about the .NET "tribe" and all the other tribes out there? I can think of several great .NET/Mono based open source GIS application and libraries (MonoGIS, Appomattox, NetTopologySuite, GeoTools.NET, SharpMap and many more). Secondly these libraries aren't even fixed to a specific language, merely a framework where you decide what .NET/Mono compatible language you decide to use when linking to these libraries. Actually you can even mix languages within the same application.

It's funny to see that people still can't see .NET as a language used for Open Source applications - probably because the big bad wolf (Microsoft) invented todays fastest growing language.

Ten ways NOT to ask a question in a developer forum:

Call me arrogant it you want, but you have probably seen some of this yourself. People sometimes seem exceptionally lazy when asking for help in a developer forum.

Here are some of the questions I often see in developer forums and that are rarely answered.

1.  "It does not work – Please help"
…if this is all you ask, how would you ever expect us to be able to help you?

2. Is this code correct? (followed by 100 lines of uncommented code snippets)
Do you really expect someone volunteer to set up a project, do what ever it takes to have your code run in our setup, fix it and send it back to you ready to implement in your project? Showing a bit of initiative, writing what this code does, where the error is, showing that you actually have been doing some debugging etc. always helps. Lots of code comments also help us understand your code without spending a lot of time analyzing it.

3. I get an error in this line: (followed by one line of code at most)
Ehm yeah so? Please state what you were trying to do, perhaps showing some previous lines of code, write WHAT error you received and preferably a full stack trace.

4. Could someone please write an application that does this and that?
Most developer forums are for helping out – not for doing YOUR job.

5. Reply to someone else’s thread, with a completely different question.
Did you ever wonder what the button "Create new thread" is for? (ex)

6. Create multiple new threads with the same question.
This tends annoy most people. Annoyed people tend not to be so helpful. Just because you haven’t received a reply within the last hour, it rarely helps asking over and over.

7. Make it clear that you never really put any effort into it to begin with.
Showing that you have actually tried working with your problem, that you have read the documentation and browsed the demos usually helps a lot to get people interested in helping you.

8. Follow-up on a question in a new thread, without referring to the previous thread.
How should we know what you are referring to? (ex)

9. Make a topic that could be about anything.
If you want people to read your post (and preferable someone who knows something about this), make sure the topic makes sense in relation to your question. It will also help people find your question later, when they run into the same problem. Topics like "Can I do this?" or "Problem" is not very appealing posts to read.

10. Ask a question in the wrong forum.
How would you expect to get help with printing from Microsoft Word in a forum about PostGreSQL?

Feel free to add some more in the comments section :-)

Using XAML for rendering maps

I was just reading a few articles on XAML - Microsoft new UI language for rendering vector content and user interfaces - when it hit me that this probably can get you much further in web mapping interaction than SVG can. XAML is part of the "Windows Presentation Foundation" a part of .NET Framework 3.0


My first attempt to generate XAML was done by creating a new renderer for SharpMap, and below you can see my first results in XamlPad. The data here has been created based on a SharpMap map by my quick'n'dirty XamlRenderer for SharpMap.




All it takes with the new renderer is initializing the new renderer with your map, and request a new map:

SharpMap.Xaml.Renderer XamlRenderer = new SharpMap.Xaml.Renderer(map);

string xaml = XamlRenderer.GetMap();


If you zip the generated XAML file you even get a 20% reduction over a PNG image.


Next step is to add interaction like zooming, querying etc…


Download XAML for the above worldmap (261,36 KB)

Applying on-the-fly transformation in SharpMap

I have received a lot of questions on how to transform data from one coordinatesystem to another on the fly in SharpMap. Usually the problem is that they have data in different coordinatesystems and want to match them. Although I would recommend applying transformations once-and-for-all to increase performance (you could use OGR for this), it is easy to setup in SharpMap. Below are some examples on how to accomplish this.

SharpMap gives you the full power to specify all the parameters in a projection. The following method demonstrates how to setup a UTM projection:

.csharpcode { font-size: small; color: black; font-family: Courier New , Courier, Monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }
/// <summary>
/// Creates a UTM projection for the northern
/// hemisphere based on the WGS84 datum
/// </summary>
/// <param name="utmZone">Utm Zone</param>
/// <returns>Projection</returns>
private IProjectedCoordinateSystem CreateUtmProjection(int utmZone)
CoordinateSystemFactory cFac = 
      new SharpMap.CoordinateSystems.CoordinateSystemFactory();
//Create geographic coordinate system based on the WGS84 datum
IEllipsoid ellipsoid = cFac.CreateFlattenedSphere("WGS 84", 
           6378137, 298.257223563, LinearUnit.Metre);
IHorizontalDatum datum = cFac.CreateHorizontalDatum("WGS_1984", 
                     DatumType.HD_Geocentric, ellipsoid, null);
IGeographicCoordinateSystem gcs = cFac.CreateGeographicCoordinateSystem(
                     "WGS 84", AngularUnit.Degrees, datum,
                     new AxisInfo("Lon", AxisOrientationEnum.East),
                     new AxisInfo("Lat", AxisOrientationEnum.North));
//Create UTM projection
List<ProjectionParameter> parameters = new List<ProjectionParameter>(5);
parameters.Add(new ProjectionParameter("latitude_of_origin", 0));
parameters.Add(new ProjectionParameter("central_meridian", -183+6*utmZone));
parameters.Add(new ProjectionParameter("scale_factor", 0.9996));
parameters.Add(new ProjectionParameter("false_easting", 500000));
parameters.Add(new ProjectionParameter("false_northing", 0.0));
IProjection projection = cFac.CreateProjection(
"Transverse Mercator", "Transverse_Mercator", parameters);
return cFac.CreateProjectedCoordinateSystem(
         "WGS 84 / UTM zone "+utmZone.ToString() +"N", gcs,
projection, LinearUnit.Metre,
new AxisInfo("East", AxisOrientationEnum.East),
new AxisInfo("North", AxisOrientationEnum.North));

If you have a well-known text-representation, you can also create a projection from this. A WKT for an UTM projection might look like this:

PROJCS["WGS 84 / UTM zone 32N",GEOGCS["WGS 84",DATUM["WGS_1984",SPHEROID["WGS 84",6378137,298.257223563,AUTHORITY["EPSG","7030"]],AUTHORITY["EPSG","6326"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.01745329251994328,AUTHORITY["EPSG","9122"]],AUTHORITY["EPSG","4326"]],PROJECTION["Transverse_Mercator"],PARAMETER["latitude_of_origin",0],PARAMETER["central_meridian",9],PARAMETER["scale_factor",0.9996],PARAMETER["false_easting",500000],PARAMETER["false_northing",0],UNIT["metre",1,AUTHORITY["EPSG","9001"]],AUTHORITY["EPSG","32632"]]

SharpMap comes with WKT parsers for parsing a WKT to a coordinate system (note: the current v0.9RC1 has a few bug in its WKT parser, but if you get problems parsing the WKT, use the current source from the repository, where these issues have been resolved)

/// <summary>
/// Create coordinatesystem based on a Well-Known text
/// </summary>
/// <param name="wkt"></param>
/// <returns></returns>
private ICoordinateSystem CreateCoordinateSystemFromWKT(string wkt)
CoordinateSystemFactory cFac = new CoordinateSystemFactory();
return cFac.CreateFromWkt(strProj);

If your data is based on shapefile data and they have a .prj file defining the coordinatesystem, you can simply retrieve the CS from the shapefile instead:

((myMap.Layers[0] as VectorLayer).DataSource as ShapeFile).CoordinateSystem

The next step is to create a transformation between two coordinate systems. SharpMap currently supports transforming between a geographic coordinate system and one of the following projections:

  • Mercator 1-standard parallel (Mercator_1SP)
  • Mercator 1-standard parallels (Mercator_2SP)
  • Transverse mercator (Transverse_Mercator)
  • Lambert Conic Conformal 2-standard parallel (Lambert Conic Conformal (2SP))
  • Albers

Unfortunately datum-shifts and transformations between two projections are still down the pipeline, but the above will be sufficient in most cases. (for those interested full transformation between all supported projections as well as datum-shifts are almost done...)

The following shows how to create a transformation and apply it to a vectorlayer (only vector- and label-layers supports on-the-fly transformations):

//Create zone UTM 32N projection
IProjectedCoordinateSystem utmProj = CreateUtmProjection(32);
//Create geographic coordinate system (lets just reuse the CS from the projection)
IGeographicCoordinateSystem geoCS = utmProj.GeographicCoordinateSystem;
//Create transformation
CoordinateTransformationFactory ctFac = new CoordinateTransformationFactory();
ICoordinateTransformation transform = 
   ctFac.CreateFromCoordinateSystems(source, target);
//Apply transformation to a vectorlayer
(myMap.Layers[0] as VectorLayer).CoordinateTransformation = transform;

Happy transforming!