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MAP 3D Geodetic Polyline Length

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Message 1 of 11
dwolford
3050 Views, 10 Replies

MAP 3D Geodetic Polyline Length

I have a MAP 3D drawing set up in LL84 coordinate system with polylines attached to object data over the USA.  I am trying to determine the geodetic distance of each 2D polyline.  The end result will be a SDF file with a database of records attached to polylines where one of the columns of data is the length of the fiber optic cable.  I already created a SDF and connected it using FDO and then used the Create Calculation and the Length2D, but the results were not correct.  Any ideas?

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Message 2 of 11
parkr4st
in reply to: dwolford

geodetic distance as in  the shortest path along the ellipsoid of the earth at sea level between one point and another.?

 

check this site http://www.vterrain.org/Misc/distance.html 

 

f1 for help and search for       geodetic distance, measuring

 

your should be able to plug the formula into a calculation in the data table for the sdf and get the geodetic distance also.

 

dave

Message 3 of 11
dwolford
in reply to: parkr4st

Thanks Dave, but I'm not quite sure that helps, unless there is a way to access the functions in the free library PROJ.4 within AutoCAD MAP.  I realize that AutoCad Map 3D has an intrinsic function "mapdist" which computes the geodesic (spherical) distance between two points.  However I would like to calculate the spherical distance between many points for a polyline and then cummulate those sphereical distances for each polyline.  I have MS Excel VBA routines that calculate the sperhical distance between two points using either the Haversign or the Vincenty formulae, but that isn't particularly useful to me as I have very little knowledge in programming AutoCAD.  I could take the very nasty approach of selecting the polyline, typing list and then coping and pasting all of the coordinates into MS Excel, parsing the data and then use my Vincenty VBA function to calculate the distances between each and every point and then cummulate.  That however would be ridiculous. 

 

What about topologies or quering the current drawing? I am aware somewhat of these tools in AutoCAD but not sure when to use them.  I am also aware of various lsp routines that will provide cummulative distances of polylines, though they are not spherical distances.  How difficult would it be to create a VBA or LSP routine that would calculate the cummulative vincenty spherical distance in AutoCAD MAP given I basically already have the routine written in Excel VBA?

 

Dan

Message 4 of 11
parkr4st
in reply to: dwolford

if i understand you, you have a polyline the for example goes from boston to nyc to chicago to denver to SLC to seattle and points in between and you want to calulate the geodetic length of each segement and  accumulate to total of all the segments.

 

if you x plode the pline to lines and send the lines to a sdf you can take along the x,y,z, coordinate property of each endpoint as data for each segment of the cable. could you use x,y,z data to do the calculations?

 

dave

 

 

 

 

Message 5 of 11
nathanwampler
in reply to: dwolford

You may have to query your drawing into a coordinate system like NAD83 or NAD27, there are thousands of different systems. When I have a drawing in LL83 I have to query the drawing (or just the polylines) into a new drawing that has been set up for the coordinate system the place is actually in like UTM-NAD83-13F (Texas) and then the polylines will be set to true length as it would be if you were actually measuring it yourself. It's a pain sometimes but if you want the true length that is the only way that has worked for me.

 

Message 6 of 11
dwolford
in reply to: dwolford

Dave I could use the x,y data to do the calculations in a spreadsheet, but this would be a major PITA.  A program that purports to be for mapping should have a few intrinsic functions that calculate the spherical distance in a more useful way then it is currently implemented in AutoCAD Map.

 

Nathan I was considering using your approach, but when you consider just how many UTM sections there are in the US, this would also be a big PITA, since the polylines would overlap many UTM regions.  It might be less work than just exporting the coordinates though.

 

As I see it the only real good way would be to program an AutoCAD Map routine that would use either the Vincenty or Haversign method to do what I need.  I am currently too lazy and busy to develp such an application.

 

The solution I did come up with was to export the polylines into a SHP file.  I then imported the SHP file into MAPINFO.  [Smartass On] MAPINFO actually has an intrinsic function that will calculate the spherical path distance of an object.[/Smartass Off].  I added a column to the table and used this intrinsic function to calculate the Spherical Object Length of each polyline for each record in the table.  I then converted the MAPINFO TAB file into a SHP file and voila, c'est finis. 

 

Incidentally if anyone is interested in some already developed Excel Visual Basic code to calculate the spherical distance using the Vincenty Method, or Haversign method I can provide you with that code.

 

Thanks for your help.

 

Dan

Message 7 of 11

Silly question, but what are you using the distance for?  If we're talking about a true geodetic distance, then wouldn't you be interested in the ups & downs and you traverse the geoid versus ellipsoidal model?  i.e. what would the odometer read as I drove from San Fransisco to NYC across the Sierra Nevadas, the Rockies (I'll give you Kansas Smiley Very Happy) etc?  Has anyone even seen a package that is truely 3D and not just 2.5D?

 

Sure I can drape a .SHP over a surface model, but I've never seen an interactive model that modifies the true 3D length as a result of the draping - wouldn't that be cool!?!  Maybe we should put it on the AUGI wishlist 🙂

Message 8 of 11

I'm determining the distance or length of fiber optic cable routes. When performing distance calculations over the sphere, elevation differences are typically assumed to be neglible.  Take for example the fiber I am working with, I seriously doubt there are very many locations where the elevation of the fiber exeeds 8000ft (1.5 mi).  When you consider the radius of the earth varies from 3950 mi at the poles to 3963 mi at the equator, that 1.5 miles will result in neglible differences in length.  However if you have ever seen old Fiber As-Builts they barely have 2 dimensional measurements let alone any notion of elevationSmiley Happy.  Ultimately I will compare these distances to the contractual distances and actual as-built distances where necessary as a means of book keeping.  The company I subcontract with pays for easements using the length of fiber in the right-of-way, therefore it is somewhat important to have a quality estimate of the length of fiber using different means.

Dan

Message 9 of 11
nathanwampler
in reply to: dwolford

When measuring for footage over hills and valleys why don't you just give yourself a 5% buffer for your footages? Also if your fiber will be buried you won't have to worry much about those unless you are actually going up mountains. With aerial you will have to worry about backspan slack footage and those are usually figured in with loops and coils. You may be putting a lot of effort into getting them exact and may never be able to (especially if you're charging by T & E).

Message 10 of 11

Can anyone respond who has experience with Autodesk Utility Design (esp communications package)?  one of my sales associates has indicated that this is along the lines of what it's supposed to do, but until I see it, I won't go out on a limb and say that the Sigma(X,Y,Z) is a true geodetic distance including an accounting for the hyperbolic distance of the sagging lines, is a reality.  Just curious if there's an "add-on" above Map3D that delves into the realm of the topic at hand....

 

Thx!

Message 11 of 11
mathieu.roy
in reply to: dwolford

I would check out the feature, right-click to extract the geometry, and then use the lengthen command to get the length of the polyline.

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