The DNRWMSCLIENT Tool



The DNR WMS Client for ArcView

Written by Tim Loesch

Minnesota Department of Natural Resources

500 Lafayette Road, Box 11

St. Paul, MN 55155

Tim.Loesch@dnr.state.mn.us

Current Version – 1.1

Build Date – 1/13/2004

Background

The DNR WMS Client is an ArcView 3.x extension developed by the Minnesota Department of Natural Resources that accesses Open GIS Consortium (OGC) Web Mapping Servers (WMS) that serve spatial data via the Internet. Of particular interest for GIS users are DOQs and DRGs available at the USGS TerraServer web-mapping site. This extension facilitates the access of TerraServer DOQs and DRGs with other site-specific spatial data within the ArcView 3.x desktop GIS program. It also provides options for saving the images at the current screen resolution as a georeferenced jpeg image or downloading a series of adjacent georeferenced images (jpegs) at various resolutions (down to 1 meter).

WMS Background

WMS services were developed to provide a standardized way of exchanging mapped data. WMS was created to provide web authors the ability to access mapped data as images that can be generated on the fly via standardized requests. The images are optimized for distribution and delivered to the user for the area they are currently viewing at the screen resolution of the display.

Storing imagery and serving it using WMS is an efficient alternative to distributing large collections of imagery to users and the associated costs of disk storage and efforts to copy and distribute the information – this program allows users to access imagery stored this way within the ArcView 3.x environment.

Installation

Unzip the wmsclient.zip file into a temp directory.

The ZIP file contains the installation program WMSClient_Install.exe. Double-click the WMSClient_Install.exe file to initiate the installation. If you didn’t get a zip file just ignore this step.

The default installation folder is c:\program files\dnrwmsclient. To complete the installation you will need to copy the ArcView extension, DNRWMSClient.avx file that is found in the newly created program directory to the ArcView extension folder (usually \esri\av_gis30\ext32).

[pic]

To access WMS servers this program reads parameters from a file that has an OGC extension. OGCs are XML formatted files that store the parameters needed to access a WMS server. There are several that are provided with this program that are found in the installation folder. It is suggested that you create a directory in a convenient location called WMSCLIENTPROJ and copy the *.OGC files from the c:\program files\dnrwmsclient directory. These are the files that you will look for when adding a WMS theme.

That completes the installation.

Using the DNRWMSCLIENT Extension

Start ArcView and load the DNRWMSCLIENT extension from the list of available extensions. A WMS Client dropdown menu and a W button will be present in the View Document Interface.

[pic]

Open a View and add a Theme that contains features that are in the same area that an image is needed. It is important that you Zoom to the desired area to a scale of less than 150,000 when you view TerraServer themes. Once you are Zoomed in use the W button to add a new WMS Theme.

A directory dialog box appears that requests the selection of a *.OGC file. The OGC file contains image availability and projection information used by the WMS site to query the requested data with the desired projection. The OGC file selected needs to request the projection that matches the projection of the local, on-site spatial data. Navigate to the WMSCLIENTPROJ directory created earlier and select the appropriate OGC file. For the purposes of this example we will be selecting the MNDNRDATADELI.OGC file which provides access to a variety of layers from the Minnesota Department of Natural Resources, GIS Data Deli.

[pic]

The DNR Data Deli WMS has several layers of information available and these will be listed in the dialog. Select the desired layer, in this case use the FSA 2003 Color DOQ option). The image for the area of interest is downloaded and added to the view with the Theme name:

FSA 2003Color DOQ

The zoom features in ArcView can be used to view a larger or smaller area and the image will automatically be refreshed for the new limits of the View area at the new scale and extent.

At this point the DOQ that you are viewing is constantly being updated as you zoom and pan in ArcView or when you change the size and orientation of the View window. Every time you change the view a new image is requested from the DNR Data Deli. This “live-link” results in the generation of a JPG image and world file in your TEMP folder that has a WMS prefix on it. Every time you zoom or pan the old file is removed from the view, deleted from the hard drive and replaced by a new one.

You can continue to use the image as a live, online backdrop but this requires that your computer must be connected to the internet for you to access the images. If you want to use these images off-line, say on a laptop computer, you can permanently save imagery to your hard disk at the current screen resolution or at a user-defined resolution. Other advantages to saving the imagery to your hard drive is that saved imagery always draws faster and is more responsive than accessing it from an Internet source and you also reduce traffic on your network.

Saving a Screen Resolution Image

Make the FSA 2003 Color DOQ WMS Theme active.

Go to the WMS Client dropdown menu and choose Save WMS Image to Disk option.

[pic]

Choose a location to store the images and specify a file name with a .jpg suffix. A .jwg file that contains the georeferencing information will also be created. This image will NOT change as you zoom and pan. The image resolution will not be refreshed so when you zoom in it will get pixilated and when you zoom out the image will not fill the view.

Saving an Image at a User-Defined Resolution

Create a graphic on the display using the rectangle tool that encompasses the area for which you want to download data. Note – you could also use the circle or polygon tool to draw a graphic however the image will not be clipped to the graphic, only a rectangular area will be retrieved.

[pic]

Go to the WMS Client dropdown menu and choose the Download WMS Tiles option.

You will be asked to select an OGC file to specify the WMS server you want to download data from. Following the previous example we will use MNDNRDATADELI.OGC

Then choose a location to store the image(s) and specify a name with a .jpg suffix. A .jwg file that contains the georeferencing information will also be created.

The WMS.DownloadImages dialog box will appear that requests the cell size (meters). Set the cell size to desired resolution, the lower the value the better the image quality but the longer it will take to download.

[pic]

Depending on the size of the area of interest that was defined to download image data, multiple “tiles” or images may be created. The naming convention is r?c?.jpg. The “r” defines the row of the image and the “c” defines the column. An image catalog called “.dbf” file is also created and can be added as an image Theme. It contains information about the multiple tiles that were downloaded. Activating this Theme automatically loads the multiple tiles to the View display and can be controlled as a single Theme. You should use this table as the Image theme in other ArcView Views and project files.

Downloading the data may take a while depending on the number of tiles that need to be downloaded and the speed of the Internet connection. However, once downloaded you are not tied to the internet and can use the imagery off-line.

Questions? Contact,

Tim Loesch

GIS Operations Supervisor

Minnesota Department of Natural Resources

Tim.loesch@dnr.state.mn.us

651-296-0654

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download