[Geomoose-users] Geomoose2 and MapServer tolerance

[Johan Forsman]

Hello All:

Before I pester anyone with one of my many questions I wish to say "Thank You!" to the authors of Geomoose, OpenLayers, and MapServer. Discovering these products just recently I have been able to, in relatively short order and in spite of exceptionally weak programming skills, assemble a usable web mapping application for internal use in our state drinking-water program. This is really quite fantastic. I simply took the demo app included with Geomoose2 and adapted it (more or less successfully) to our needs. So far I have only needed to invest time and aspirin, a bargain by any measure.

Now, on to question one of several thousands:

Not counting the base map data, our data are mostly for water-well locations in point form. I have projected all data to NAD83 UTM15N using my desktop GIS application prior to uploading it for use with Mapserver.

The identify tool works quite nicely, but I am having some issues with the tolerance. Specifically, it appears the tolerance is not recalculated when the scale changes. If I use ground units (meters) in my map file I would expect this to be the case, but if I use pixels I would expect the linear distance represented by one pixel to change depending on the scale.


The map is 800x650, and maximum extent is at just under 1:3 million.
If I use pixel units and a tolerance of 1, my back-of-envelope calculation estimates each pixel at ~850 meters or so. If I zoom in to 1:24000 and use the identify tool, it will still return every well in an ~850 meter radius. This becomes problematic.

Using units of meters I can clearly be much more selective, but then on the other end of the scale I can't hit anything "just right" to obtain any results.

If anyone can enlighten me I would be most grateful, and if I am missing something completely obvious and by this am wasting everyone's time, I apologize in advance.

Respectfully,
Johan.

----------------------
Johan Forsman, M.Sc.
Geologist
Safe Drinking Water Program
Louisiana Department of Health and Hospitals
Office of Public Health
Telephone: 225.342.7309
Telefax: 225.342.7303