Display Route Events produces strange output

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05-20-2013 11:03 PM
wolfgangobruca
New Contributor
Hi, Forum!

Im running into some issues when trying to display Route events (Points with length data) within a river catchment.
Here`s the point of departure and the way I tried it:

I got 51 fish sampling points evenly distributed over the Austrian river network. For each of these points I do have data on the length of the fished stretch (between 200 and 6500 meters for each point) and whether the sampling was conducted upstream or downstream of a point. In order to get a polyline imprint ffor each of those 51 sampling points, I was trying the "locate features along routes"-tool to get their location at the river network (units in meter). Curiously, after providing the tool with the correct Route identifiers, the measured distance (meas field output in the attribute table) for each point is way too short (always somewhat between 0 and 600 m) although a river route may be greater than 1500 meters in length. Still, although those numbers are to small, their location seems to follow a correct ratio (e.g. if i got 2 fish points in a row, one would show me 150 m and the upstream one 180m)
However, next I was using the meas data and the fished length data on the "display route events" option. For upstream lengths, i calculated "meas + fished length" and vice versa for the downstream fished lengths ("meas - fished length").
The result is a polyline shapefile where every single length is  overestimated at large scale (sometimes more, sometimes less).
I hope you can help me with this,

thanks in advance

Wolf
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RichardFairhurst
MVP Honored Contributor
Hi, Forum!

Im running into some issues when trying to display Route events (Points with length data) within a river catchment.
Here`s the point of departure and the way I tried it:

I got 51 fish sampling points evenly distributed over the Austrian river network. For each of these points I do have data on the length of the fished stretch (between 200 and 6500 meters for each point) and whether the sampling was conducted upstream or downstream of a point. In order to get a polyline imprint ffor each of those 51 sampling points, I was trying the "locate features along routes"-tool to get their location at the river network (units in meter). Curiously, after providing the tool with the correct Route identifiers, the measured distance (meas field output in the attribute table) for each point is way too short (always somewhat between 0 and 600 m) although a river route may be greater than 1500 meters in length. Still, although those numbers are to small, their location seems to follow a correct ratio (e.g. if i got 2 fish points in a row, one would show me 150 m and the upstream one 180m)
However, next I was using the meas data and the fished length data on the "display route events" option. For upstream lengths, i calculated "meas + fished length" and vice versa for the downstream fished lengths ("meas - fished length").
The result is a polyline shapefile where every single length is  overestimated at large scale (sometimes more, sometimes less).
I hope you can help me with this,

thanks in advance

Wolf


The logical explanation is that the measures of your route are not in meters, since all of your results are consistent with that condition.  Although what unit of measure it is using is unclear from what you have described.  Route measures can be in any conceivable unit length, including random lengths, depending on how they were built.

On your routes, go to the properties and apply hatching of your measures to see what is actually stored on your route lines.  Then use the measure tool to determine the length between several pairs of known hatches to see if there is an obvious unit ratio difference that consistently defines your route measure system.  There are ways to have the Routes remeasure themselves based on lengths (unit conversion multiplication with the Route editing tools, rerunning the Create Routes tool, etc), but which is best for your situation depends on how many routes you have, whether the current routes have a consistent unit differential to meters, the amount of route branching and looping, etc.
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