Black areas in Silverlight Map Control using GeoWebCache

Strange behavior in Silverlight map control (SMC).

This blog from Randy George shows how to use GeoServer GeoWebcached layers in the Silverlight map control:

http://www.cadmaps.com/gisblog/?p=54

Very nice, works well. I used this syntax for my Tile Source

MyBase.UriFormat = http://ogi.state.ok.us:8080/geoserver/gwc/service/gmaps?layers=ogi:okcounties&zoom={2}&x={0}&y={1}

which pulls tiles from the GeoWebCache.

Problem is, some of our layers have a smaller coverage area than others. GeoWebCache is smart enough to not try to generate tiles if the layer doesn't cover the area. Problem is, that the SMC shows a tile that doesn't return data as BLACK. Very ugly - see picture.

So, how to fix? Likely this is a bug in the SMC, so it needs to be fixed there. But in the meantime, you can change the extents of your GeoServer layer to be larger. Then, reload the GeoWebCache by going to the http://yourserver:8080/geoserver/gwc/demo and clicking on "Reload Configuration" - or possibly restarting GeoServer, I didn't try that.

Then GWC will send back transparent PNGs instead of nothing at all, and the SMC is happy.

Adding Personalization to ASP.NET with PostGIS (PostgreSql)

Next step - adding personalization to the web site using Postgresql.

Very easy, as well as documented.

Just go to:

http://dev.nauck-it.de/aspsqlprovider/

and follow the directions.

One thing not mentioned is the PostgreSQL encoding of the database when you create it. I used the default Win1252, which seemed to work fine.

I created the database, ran the SQL script to create the tables, and added/modified the web.config file.

Created a asp.net web form with a login control, ran it, but it didn't work. Got:

at NauckIT.PostgreSQLProvider.PgMembershipProvider.ValidateUser(String username, String password) in C:\Users\Daniel Nauck\Documents\Visual Studio 2008\Projects\PostgreSQLProvider\PgMembershipProvider.cs:line 1229 at System.Web.UI.WebControls.Login.AuthenticateUsingMembershipProvider(AuthenticateEventArgs e)

Well, that was a bit disconcerting. So, looked at the Immediate window in VS2008, for more info, and saw:

Npgsql.NpgsqlException:
syntax error at or near "("
Severity: ERROR
Code: 42601
at Npgsql.NpgsqlState.d__a.MoveNext()
at Npgsql.NpgsqlState.IterateThroughAllResponses(IEnumerable`1 ienum)
at Npgsql.NpgsqlState.ProcessBackendResponses(NpgsqlConnector context)
at Npgsql.NpgsqlReadyState.Flush(NpgsqlConnector context)
at Npgsql.NpgsqlConnector.Flush()
at Npgsql.NpgsqlCommand.Prepare()
at NauckIT.PostgreSQLProvider.PgMembershipProvider.ValidateUser(String username, String password) in C:\Users\Daniel Nauck\Documents\Visual Studio 2008\Projects\PostgreSQLProvider\PgMembershipProvider.cs:line 1210
A first chance exception of type 'System.Configuration.Provider.ProviderException' occurred in NauckIT.PostgreSQLProvider.DLL

Not too helpful...

Then tried various things, made sure the uid and password was ok, changed the name of the application to the name of my project, etc. These had no effect.

Then, did a get of the latest Nauck from SVN and added to my solution. Then it started working. Perhaps the release 1.240 is a little bogus? Anyway, now it works. Awesome.

Converting a Lat Long to a USGS Quarter Quad Number in VB

USGS uses an odd system of numbering the 24k quads, and quarter quads.
it uses lat, lon(lower RIGHT corner), then letters A - H from right to left, and 1 -8 from bottom to top. Quarter quads are then numbered 1 is upper right, 2 is upper left, 3 is lower left, 4 is lower right of the whole quad. eg 33106-E32 where the 2 at the end is the qq number.

An irritating little problem, but here is a solution in VB.net


Given a lat-lon, what is the USGS quad number (or USGS quarter quad in this case)

Private Function LatLonToQQName(ByVal Latitude As Double, ByVal Longitude As Double) As String

'What is the Longitude whole number part (degree) of the right corner
Dim LonDegree As Integer = Math.Ceiling(Longitude)

'Get the fractional part of lon
Dim FLon = LonDegree - Longitude

'Calculate the Number, from 1 to 8, starting from right corner
Dim Number As String = Math.Ceiling(FLon / 0.125).ToString

'Next, the number, from 1 to 8, starting from bottom
Dim LatDegree As Integer = Math.Floor(Latitude)

'Get the fractional part of lon
Dim FLat = Latitude - LatDegree

Dim Letter = Chr(Asc("A") + Math.Floor(FLat / 0.125)).ToString

'Finally, the QQ number (from 1 to 4) 1 is upper right, 2 is upper left, 3 is lower left, 4 is lower right
Dim QQNumberLon As Integer = Math.Floor((FLon / 0.125 - Math.Floor(FLon / 0.125)) * 2)
Dim QQNumberLat As Integer = Math.Floor((FLat / 0.125 - Math.Floor(FLat / 0.125)) * 2)

Dim QQNumber As String = ""
If QQNumberLat = 0 And QQNumberLon = 0 Then
QQNumber = "4"
ElseIf QQNumberLat = 0 And QQNumberLon = 1 Then
QQNumber = "3"
ElseIf QQNumberLat = 1 And QQNumberLon = 1 Then
QQNumber = "2"
ElseIf QQNumberLat = 1 And QQNumberLon = 0 Then
QQNumber = "1"
End If

Return LatDegree.ToString & (Math.Abs(LonDegree)).ToString("D3") & "-" & Letter & Number & QQNumber
End Function