When we first set up the NYSDOT Milepoint ALRS in Roads and Highways years ago, we explicitly set the X and Y tolerance and resolution using standards we used elsewhere in the NYSDOT GIS environment and the M (measure) tolerance was set automatically as shown below. Our assumption at the time was the measure tolerance had been set to the most appropriate value based on the desired X/Y tolerance. While that is true, I do not believe this M Tolerance (0.000000621369949 miles) is compatible with our Measure Precision of 7.
Since our Milepoint ALRS has been in production, we have seen unsettling issues with tiny mismatches in length between centerline (geometric) length, route end measure and event end measures.
After comparing with the North Carolina DOT ALRS Resolution and Tolerance properties, I believe that the measure tolerance on the network should be set simply based on the measure precision as shown below.
If Measure Precision (decimal places) = 6 then...
Measure Tolerance should be 0.000001 miles (five zeros right of the decimal point)
If Measure Precision (decimal places) = 7 then...
Measure Tolerance should be 0.0000001 miles (six zeros right of the decimal point)
Note that since NYSDOT uses measure precision = 7 our current M tolerance of 0.000000621369949 miles is greater than 0.0000001 miles. Does this extra "wiggle room" in tolerance create the inconsistent end measures on routes and events that we have seen in our network?
So a few questions for he group…
For the Esri SMEs or product team:
- I didn’t see more information on aligning the Measure Precision and Tolerance settings in the attached white paper. Do you concur with the “if…then” statements above or is my brain playing tricks on me with a whole bunch of very small numbers?
- If we decide to update our ALRS to reset the measure tolerance, I understand that we need to start from scratch and reload the network and event feature classes into it. Could you guide me to the best process/documentation to do that?
For the rest of the RHUG community:
- I'm curious how other well established RH ALRSs are set up for M precision and tolerance. Would you could your LRS Network Properties for Resolution and Tolerance Properties shown below and post them here as something like the following example:
New York (NAD83 UTM Zone 18N):
Measure precision: 7
X/Y Tolerance: 0.001 meters
M Tolerance: 0.000000621369949 miles
Many thanks! Kevin