GPS coordinates

[charliep]

I've been asked to specify the layout of a building showing the various points as gps coordinates. I did this many moons ago with Autocad but can't seem to figure it out in Revit. Any advice most welcome.

[irneb]

Unfortunately Revit doesn't use the GPS "location" as anything to tag to. It's only used to calculate sun positions for shadow studies.

You might be able to adjust your survey coordinates to match the datum's GPS coordinates - but that's going to be a hit-n-mis method and I'd not trust it too much (the further away your datum is the worse the accuracy).

Sorry if you know all this, but I've found lots of people misunderstanding the difference between survey coordinates and GPS:
A GPS device is very seldom more accurate than 10m (around 33'), the best I've seen is no more accurate than 1m (around 3') - and even then it's dependant on weather conditions, device calibration, how many satelites are in direct line-of-sight, how long you leave the device in one spot, etc.etc... Good enough to get a general location, but I'd not build from it. Some of the newer coordinate mappers use GPS to position themselves generally, then need extra calibration by adjusting to known landmarks - from then you never again move the transmitter until you are finished - you move the receiver which isn't actually a GPS device - it simply maps the direction / asimuth / distance from its current location to the stationary transmitter (usually using lasers or radio) - these are the only "GPS" devices remotely accurate enough to build with (forget something like a Garmin).

Depending on where on the globe you are, you would generally use one of the UTM grids: http://www.dmap.co.uk/utmworld.htm See these as some planes as facets placed around a elipsoidal sphere (note the earth isn't even 100% spherical). So converting from one UTM zone to the long/lat of GPS is nearly never a straight forward formula - you're mapping from a plane onto a curved surface.

I suppose you could manually convert the survey coordinates UTM to GPS coordinates using some convertion tool and then manually add text to "tag" these on your view. There are some tools available for such, e.g.: http://coordtrans.com/coordtrans/

Are you sure you don't mean survey coordinates? These are usually given to an accuracy of 10mm (around 2/5") and is usually the coordinate system used when a surveyor maps your site using a theodolite. Might be to some local grid system or one of the UTM grids. Those you can easily tag with Revit once you setup your survey location (direction to true north, easting / northing, and elevation) compared to your project location (some arbitrary point and direction following the building you're drawing, usually a grid intersection and a 0 level).

[charliep]

irneb that's brilliant. Yes survey coordinate is exactly what I mean. Do you know if there is an "Idiots Guide to Survey Coordinates for Revit"? I think that's what I could do with right now.

[irneb]

First you might want to look at this thread: http://forums.augi.com/showthread.php?105452-Project-Coordinates-Shared-Coordinates-and-the-new-Survey-Point

Next, there are some tutorials (some linked to in that thread), you could google for them. But I've found most of them are more interested in discussing shared coordinates - which is something you only need when linking RVT/DWG files and they tend to just glance over how to actually set up Project and Survey origins. Strange though - shared coordinates are actually an old thing, while the Project/Survey was only recently changed (you'd expect new tuts to focus on the new thing wouldn't you?)

Anyhow, I'm working on a video tut for this exact thing for my office - since this has been one of the most asked for "Help me do this" questions around here. Once I've got it sorted I'm willing to post it here too.