The controls on this page allow you to modify a WCPS query which is sent to the server when you hit the Execute button. The X and Y sliders can be used to select a geographic bounding box to subset the portion of the image displayed. (Or you can directly enter the coordinates in the text boxes.) The Z slider can be used to highlight a certain depth range (in blue). So, for example, if you slide the upper handle of the Z slider to 10 you will see all areas lower than 10m above sea level. The WCPS query generated can be viewed and edited in the box above.
This illustrates both the processing that can be done to present non-image numerical data in a visual way and reducing the size of data that is actually retrieved over the web from the full source data set size. Retrieving an image of the whole dataset can take up to half a minute but queries on subsets of the data may take only a few seconds. See for example these two queries around the River Thames colouring blue all areas below , , , or .
When you click the "execute" button the map and query will appear. Click anywhere on the map to close it.
The DTM here is a 2D square grid coverage with a single elevation value for each grid cell. The X and Y coordinates are British National Grid Eastings and Northings. It is 13201 x 24801 grid cells in size which uses approximately 1.4Gb. The elevation values go from -3 to 1346m. There isn't an explicit null value in the data set at the moment, all nulls were set to 0 so the sea areas have an elevation value of 0.
The WCPS query has the following components: