Effects of US Survey Feet or Intl Feet on InRoads Site

Do NOT mix the two!

The working units are controled by MicroStation, not InRoads.

The International Foot is the US Foot truncated after the sixth place post decimal. That may not sound like a significant difference but in a geometry alignment you will notice a difference in the bearing of your tangent sections resulting in a shifting of the point of end.

If you have surfaces in the other working unit you need to have your surveyor regenerate the surface in the correct working units.

You can transform you DTM from INFT to USFT using the Edit Surface Transform Surface.  I agree do not Mix, should be very careful about having INFT files kicking around, as mentioned they will be off by 2ft for every one million FT and in state plane coordinates that is significant. 

Make sure the MicroStation Design File has the proper working units defined before STARTING InRoads, do not change the units while InRoads is active because it appears to read the units when it is starting up, and will not follow the units of the design file if they are changed while InRoads is active. Processing the survey data with the proper units defined is important.

The INFT is a mistake as I see it.  The international community and what appears to be non technically inclined persons made a new unit to suit their purpose (make it easy) but since the International Community does not use the FT they should just leave it alone and let those who do, worry about the conversion factor.

Maybe I'm wrong, but I dont see InRoads treating the DTM differently, whether my drawing is in Meters, Feet or Intl. Feet. I started up inRoads, opened a drawing in meters, opened a DTm, displayed the perimeter and snapped to a corner of the perimeter to get coordinates

I exited out of InRoads, started it up again, opened a drawing with FT as the working units, opened my DTM, displayed the perimeter and snapped to the same corner. I get the same coordinates as I did for the drawing with working units set to Meters.

I repeated the whole process, but this time with a drawing in Survey Feet. Again, I get the same coordinates when I snap to the corner of the DTM perimeter.

This makes me think that the DTM is "unitless". I would assume that if the DTM had units, it would convert them to units of the active drawing so that the DTM would display in the correct coordinates. This is not the case. Am I missing something?

The reason for me bringing the issue up may be easier to explain with a picture. Please keep in mind, that the issue is specifficaly related to InRoads Site Modeler, which I have never used before. We were working on this project using InRoads DTM's, and I thought it may be a good idea to give the Site Modeler tools a try. I created a Site, and created an existing ground surface, based on my existing ground DTM. When Site Modeler displays the surface, the boundary does not match the original DTM boundary. However, the contours seem to match (for the most part, although I have also noticed some differences in certain areas).

If you look at the attached image, you can see where the contours appear in the correct place, but the DTM boundary created by site modeler is shifted. This may not be a problem, but it makes we wonder if site modeler isn't doing anything else wrong....

I believe you are correct that the DTM is unitless. However, if you start InRoads in an empty file and realize the units are wrong and change them, you must save settings and open a different file and then come back to the original file to force InRoads to read the files new, corrected units.

By your picture, it would seem that the site modeler is adjusting the units somewhere along the line. are you sure your survey feet are really defined as survey feet and not simply renamed international feet units. I have seen files that claimed to be in survey feet but they responded to scaling commands as though the file was international feet.