1. WMS launch error '...image too large...' or '...Service Error Code:InvalidDimensionalValue...'
For safety reasons and for the correct dimensioning of the servers offered by the geoservices, there is a limit to the volume of images that are generated as result of a WMS request. The volume is conditioned by the dimensions of the requested image (in pixels) and by the amount of geographical information that must be included.
Working in a conventional screen environment (screen resolution of 96 dpi) and with the scale range limits defined in the geoservices, the requests generated normally never lead to a resulting image that exceeds the maximum volume allowed by the server.
Despite this, it is very common for the servers to return an error when a request is made from a client application involving a higher resolution, which often happens when printing or exporting to certain formats (e.g. PDF). This error can be shown in different ways, depending on the server and how the client application treats the messages it receives from the server. However, what normally happens is that the WMS layers cannot be visualised, or a 'the image is too large' type error is displayed.
Solutions:
- For viewing, request smaller images or with less information.
- For high resolution printing, download corresponding files from the main viewer .
2. Loaded layer is not displayed
Some services have layers with visualisation limits depending on the scale of representation. This scale is calculated in accordance with two parameter types:
Measurements of the requested image: those which are indicated by means of the width and height parameters.
Geographical extension requested: that indicated with the two coordinates (xmin, ymin, xmax, ymax) specified in the BBOX parameter.
The relationship between these two parameters determines the scale of the image according to the formula below:
The visibility of a layer will depend on the specified scale being within the range of visualisation which has been specified by the service administrator and which may be consulted in the definition of layers of each service (range of scale fields) within the same document. If the desired scale does not fulfil this condition, the result returned by the server will be a blank image.
Another aspect must also be taken into account. Above we calculated the desired scale using the abscissae (xmax and xmin coordinates) and the width of the image, but this calculation can also be made using the ordinates (ymax and ymin coordinates) and the height of the image:
If the two formulae do not match, this will result in a deformed image, given that the vertical and horizontal scales are not the same.
These ranges are showed for each available service .