Dear MapServer Community,
we have faced an issue with the click tolerance for WMS GetFeatureInfo requests
when using custom map symbols. We use a custom .svg vector image to display
points in most of our maps.
As I understand it, the TOLERANCE parameter only defines a radius around the
point. Therefore the shape of the clickable area is always a circle.
This does not match our symbol at all and results in a bad user experience.
Essentially, only the very tip of the image is actually clickable.
I have created a demo page for demonstration purposes. Please visit
https://koelngis.stadt-koeln.de/koelngis/portale/mapServerClickTolerance/ to
experience this problem yourself.
- The layer with orange symbols is a WMS layer that demonstrates the problem I
described above. It is terrible to work with since most users instinctively
click on the white circle but actually have to click the tip to get a GFI
response. I have added an additional point layer that shows the clickable area
defined by the TOLERANCE setting.
- The layer with blue symbols is a WFS layer that works perfectly fine (since
the click is handled client-side). This is the desired behavior for WMS
requests as well. We cannot always use WFS due to client performance
constraints.
We would like to configure the MapServer so that the entire shape can be
clicked precisely. However, we could not find this capability in the
documentation. Please let us know if it is possible.
Offsetting the symbol so that the white circle matches the clickable point is
not an option because then the tip would indicate that the feature is at a
different location.
If it is in fact not possible and any commercial service providers are reading
this mailing list:
Feel free to send me a quote to opensource-mapser...@larsbaum.slmail.me. We
would like to pay someone to contribute this functionality for .svg vector
images to the MapServer open source project.
For reference, this is how we configure the symbol in the mapfile:
SYMBOL
NAME "droplet"
TYPE SVG
IMAGE "../svg/dropletShape.svg" # You can grab a similar .svg file from the
website linked above.
ANCHORPOINT 0.5 1 # Make sure the tip of the shape is centered on the point
END
# …
TOLERANCEUNITS pixels
TOLERANCE 10 # Radius of the clickable circle around the point
CLASS
NAME "Some Name"
STYLE
SYMBOL "droplet"
SIZE 40
END
END
Thank you very much for your help!
Yours sincerely
Lars Baum
GIS Developer
City of Cologne - The Lord Mayor
Office for Information Processing
Competence Center Geoinformationsystems
Auf dem Hunnenrücken 3
50668 Cologne, Germany
Mail: opensource-mapser...@larsbaum.slmail.me
Note: I'm using an alias mail to protect my business mail account from spam.
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