Just returning to my earlier post; using the Openscales API and combining WFS and WMS in one place. The goal was to use a styled map image (returned by a WMS call) and use Flex to draw the features on this image (via a WFS call), to give interactivity. One problem I found was that we needed to give the WFS drawn features a transparency of 0. This way we could get the interactivity (eg click on feature and get attributes pop up) but not see the drawn feature. But, suppose we want this selected feature highlighted in a different colour? Since the transparency is set to 0, the highlight will not be visible. How to get around this ....
Remember the Openscales map is constructed with multiple layers (imagine looking down at multiple sheets of tracing paper, on one there is a road drawn, on another a river etc all lined up correctly geographically). Our WFS (selected) layer is on one of these sheets. So all points marking well, for example, are on this one sheet. But all the points on this sheet have a transparency of 0, so they are there, but invisible. Now it is the sheet or layer which is set to 0 transparency not individual points (polygons or lines) The solution to being able to highlight a selected point (WFS feature)
......
Set a blank map feature layer. Set the transparency to 1. When a point is selected copy this to the blank layer. Hey presto it appears, Make sure when you unselect the point you both copy the point back to its original layer and then clear the blank layer.
Showing posts with label WFS. Show all posts
Showing posts with label WFS. Show all posts
Monday, August 2, 2010
Tuesday, July 27, 2010
Flex - Styling Interactive Maps
I had an interesting question recently. This was with regards building a mapping application using the open source mapping Flex library Openscales. He wanted to improve the styling of the map layers, but still be able to click on a feature and return attributes. Now Openscales is nice since both WMS and WFS calls are easy.
Let me step back quickly and explain the difference between WFS and WMS. Both involve calls to a spatial server, in this case to Geoserver. WFS returns the raw data. So Flex is able to draw the boundaries of features, making the feature interactive. The features attributes are also returned. Thus a click on a feature can return the features attributes without a additional server call. WMS simply returns an image. Getting the attributes for the latter would require both an additional server call and constructing a new query.
It struck me after thinking about this for a while. Why not combine WFS with WMS. Thus request both a styled WMS image and draw on this the WFS features. Make the WFS feature fully transparent, thus only the WMS styling shows.
After playing with this, the results were pleasingly good. The one thing I'm finding is challenging is the ability for a selected WFS feature to be highlighted when selected. Since it is fully transparent.
I have a potential solution. And will share once I have tested
Let me step back quickly and explain the difference between WFS and WMS. Both involve calls to a spatial server, in this case to Geoserver. WFS returns the raw data. So Flex is able to draw the boundaries of features, making the feature interactive. The features attributes are also returned. Thus a click on a feature can return the features attributes without a additional server call. WMS simply returns an image. Getting the attributes for the latter would require both an additional server call and constructing a new query.
It struck me after thinking about this for a while. Why not combine WFS with WMS. Thus request both a styled WMS image and draw on this the WFS features. Make the WFS feature fully transparent, thus only the WMS styling shows.
After playing with this, the results were pleasingly good. The one thing I'm finding is challenging is the ability for a selected WFS feature to be highlighted when selected. Since it is fully transparent.
I have a potential solution. And will share once I have tested
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