Hi! All! I am trying to rebuild the topography from the contour lines provided in NYC’s models for its neighborhood. However, I was not able to find out what is the vertical height difference between each contour line. I could not find it in NYC’s website. Does anyone know what the number is? Thank you!
Wow, that’s pretty amazing - NYC actually putting out geodata in Rhino .3dm format. Normally it’s all something like .dxf.
What’s surprising is that the contour lines are flat - and at some weird level - which is different for different files… Usually when data is in 3D format, the contour lines are already in 3D at their correct elevations. Funny because the structures are at different 3D elevations.
In the US, contour lines are generally in feet (or some multiple) increments - the model files are in feet - whereas elsewhere they are generally in meters or some multiple. So given the density of the contour lines and the general flatness of New York, I suspect they are in one foot increments. I looked at Central Park, which has roadways and paths that pass under bridges in spots, and I counted the contour lines there - mostly somewhere between 12 and 15 lines, so I’m going to hazard a guess that the contour lines are indeed in one foot intervals. Just my guess, mind you.
I think @Helvetosaur is spot on.
I started down that same path of discovery yesterday evening and was rudely reminded how grossly inadequate this little 13" MBP is for large files.
Mitch to the rescue.
His assumptions are correct.
1 foot contours. The Datum is a mystery as well.
@Helvetosaur@John_Brock I actually think the contours are 1 meter increments despite the rest of the model being in feet based in the New York State Plane Coordinates, Long Island East Zone, NAD83, US foot (EPSG:2263) datum per the NYC github.
When I checked the Lidar point cloud against the DEM provided by the state (REST service), the elevations seem to match. The point cloud also matches the building geometry from the Rhino file, so I believe Rhino model, Lidar point cloud and DEM are all at the same scale. The pink lines in the image below show a 1 foot contour of the DEM at the Carey Tunnel entrance in the Battery, which you can see is much more frequent than the black contours lines that come with the Rhino file.
Note, according to the metadata, the contour lines in the file are generated from a survey from 2006, so areas like the World Trade Center are not updated.
Hi! All! Thank you for your help! Actually now testing all your suggestion and finding more info from the existing survey, I found out the topo elevation interval might be 2’ in between. Thank you, however!
Since the distances between each topo line in NYC model’s topo approximately match the ones in the survey for President Grant’s tomb, I match the height of each interval accordingly. The result seemed to match.
