[mapserver-users] Inconsistance between display and data

[Jeff McKenna]

On 2016-02-16 9:15 AM, jeansomers wrote:
> Hi,
> I'm one of two base map administrators for a MapServer web-based
> application.
>
> We're regularly integrating new base map data, from reception through
> quality check to real integration.
>
> A while ago, I noticed a base map inconsistance: the map displayed a railway
> following the coast in a small peninsula.
>
> I can tell there is no railway there, I already went to the place. That's
> the beginning.
>
> So I asked for a correction from the regional administrator, which delivered
> me a new version of the local data.
>
> I checked a last time and discovered that the railway was still on the
> MapServer application.
>
> I loaded the original data in QGIS,  applied the usual symbology : no
> railway.
> I checked the attributes: no railway values in the symbology field.
>
> My colleague suggested it came from an overlapping data: we checked the tile
> indexes of neighbouring data; none was overlapping on the railway tracks.
>
> There we are, without a clue about the origin of this inconsistance.
>
> I forgot to mention that we repeatedly deleted application and client caches
> inbetween.
>
> So if you have any idea where it can com from, your suggestions are
> welcomed.
>
> For your notice, here is the print screen of the issue
>
> <http://osgeo-org.1560.x6.nabble.com/file/n5250812/33236_0001.png>
>
>

Hi,

I've been in that boat before for clients with huge mapfiles and 
mysterious artifacts in their applications, so I feel your pain.

How I always solve it, as painful as it sounds, is:

- make a copy of the mapfile used in the application
- using the copy of the mapfile:
   - change the EXTENT to the problem area
   - use the commandline utility shp2img and start removing layers and 
re-running shp2img to see where that layer exists
     - if you have 1000 layers, remove the last 500, re-run shp2img, if 
the problem data still appears in the map then remove the next 100, 
re-run shp2img, etc. etc.

Using the commandline you avoid any odd issues of applications, caches, 
and you can see the errors directly.

Good luck,

-jeff




-- 
Jeff McKenna
MapServer Consulting and Training Services
http://www.gatewaygeomatics.com/