Dealing with missing traverse information in COGO

[DannyDong]

Dear fellow parcel editors:

To be able to construct a curve using COGO, you would need radius, chord length and chord direction, for example. What if you miss some information (like chord direction)? Will Parcel Fabric be flexible enough for me to continue without that info, then get back to fill in the missing information? What we are doing now is to use a different start point, then go all the way back to the curve. Thus we can close the parcel without needing the chord direction. However, if the traverse consists a couple of such curves, then we are at a loss what to do. Can we start serveral new segments, then somehow link them together? Do you have such an experience and figured out a solution? Please share with us. Thanks in advance.

Danny

[Zeke]

If it's the chord direction you're missing, you can figure that out yourself if you know the start and end point of the arc. Just snap a line between the two arc endpoints, rightclick the line and click on direction/length. This will give you the chord direction. We have to do this when the surveyors give us bad measurements.

[DakeHenderson]

When I click on the line, there is no such option as "direction/length" or even "Properties", regardless if its created in COGO or using Create Features.. Is this a deprecated feature do you think?

[DakeHenderson]

I've realized that if the incoming and outgoing straight courses are both tangent to the curve, the deflection angle from the incoming course to the chord is simply Delta / 2, and can be used to calculate the chord direction

[TimHodson]

Hi Danny,

Here are some ideas and approaches that may help.

1. Using the grid over-rides for non-tangent curves: When adding new parcels to the parcel fabric, if you are missing certain information such as the chord bearing for a non-tangent curve, you may still have the radial bearing, or the tangent bearing. Sometimes you may have a radial bearing and it is not explicitly present on the curve itself, but may be inferred from the surrounding information. If you have one of these other bearing parameters, then you can use a grid over-ride to enter the value.

As an example of the radial bearing over-ride, if your plan properties are set to use chord bearing, but you want to enter the bearing as a radial bearing, then you can type the following:

S75-27-27E rb

In the above string the quadrant bearing portion defines the radial bearing in a direction toward the center of curve. The �??rb�?� is a suffix placed after the bearing to indicate that the bearing is to be interpreted as a radial bearing instead of the default chord bearing.

After you enter the radius and the other curve parameter for the line, and hit enter to start the next course, then the chord bearing will be computed for you and placed in the grid cell, replacing the over-ride string that you typed.

2. For tangent curves, if the curve runs tangent from the prior line(or curve), then you can use the �??*�?� to indicate the curve (or line) is tangent to the prior course.

There are a number of over-rides explained at the hyperlink called About entering lines on the parcel details lines page.

3. Otherwise, if you have 2 non-tangent curves on the same parcel, and neither of them have any information at all to help specify the orientation of the curves (no chord bearings, no radial and no tangent bearings), then that would require entering the other surrounding line information into a construction. If you have some examples that you�??d like to share, that would help. Using a construction and entering the surrounding lines may (depending on what you have) allow you to establish the end points of the curves that have the missing data. This may even mean entering parcels from an adjacent block into the construction, and using a connection line to establish the end points for the curves.

If you have a plat you can attach as an example, I may be able to give further ideas.

-Tim

[AndrewThorup]

I am having the exact same problem.  I am trying to edit a parcel in parcel fabric.  The plan I am working off of gives the following values:

Delta: 70°39'45"
Radius: -45
Tangent Length: 31.90
Arc Length: 55.50

Using the "Curve Calculator", I also have calculated the Chord Distance (52.049') and the Chord Height (8.289').  All of this information is great, but I do not have values for either the Chord, Radial, or Tangent Bearing.  Is it possible to calculate a bearing from the given values?  I realize I could find the end points by saving the curve as the final piece of the parcel, but some parcels have two or three curves in them, making that a flawed approach.  I have attached a copy of the plan I am working with for reference.  Danny - Have you figured out a way to deal with the issue?
Tim - Any advice given the values presented?  I do not mean to hijack this post, and if this would be better off as it's own post, let me know and I will create one.

Thanks,
Jay

[ChrisBuscaglia]

I am having the exact same problem.  I am trying to edit a parcel in parcel fabric.  The plan I am working off of gives the following values:

Delta: 70°39'45"
Radius: -45
Tangent Length: 31.90
Arc Length: 55.50

Using the "Curve Calculator", I also have calculated the Chord Distance (52.049') and the Chord Height (8.289').  All of this information is great, but I do not have values for either the Chord, Radial, or Tangent Bearing.  Is it possible to calculate a bearing from the given values?  I realize I could find the end points by saving the curve as the final piece of the parcel, but some parcels have two or three curves in them, making that a flawed approach.  I have attached a copy of the plan I am working with for reference.  Danny - Have you figured out a way to deal with the issue?
Tim - Any advice given the values presented?  I do not mean to hijack this post, and if this would be better off as it's own post, let me know and I will create one.

Thanks,
Jay

Jay, from that plat it looks like all the curves are assumed tangent.  You can either set the plan properties to reflect this or use the * symbol in the bearing field to set it to tangent (type the radius and arclength).

Maybe I'm missing something, please let me know if I'm not understanding.

[AndrewThorup]

Jay, from that plat it looks like all the curves are assumed tangent.  You can either set the plan properties to reflect this or use the * symbol in the bearing field to set it to tangent (type the radius and arclength).

Maybe I'm missing something, please let me know if I'm not understanding.

Chris, thank you for your response.  I tried creating a curve by entering an * in the bearing field, then typing the radius and arc length.  When I do this, a value is entered into the bearing field for the curve as well as for the next line segment.  Neither of these values create a bearing that places the curve as it appears in the plan.  I have a couple of additional questions based on your post:

• 1. How does one come to the conclusion by looking at a plat that all curves are assumed tangent? ( I did not see this written anywhere on the plat itself)


• 2. From the documentation I have read, when you place an * in the bearing field, the value that gets populated is the tangent bearing from the previous line.  The value that gets populated in the bearing field for the next line segment is the exit tangent to the curve just created.  Is that correct or am I way off?


• 3. Is there any way to calculate the degrees, minutes, and seconds for a tangent, radial, or chord bearing given the values I listed in my previous post?

Any input would be extremely helpful.

[TimHodson]

Jay,

I've made this short video that should address your questions. It shows how you can use the over-rides to enter a circular curve with any combination of 2 geometry parameters and any of the 3 orientation parameters. You use these to by-pass the current Plan settings, described starting around [5:20] in the video, and I think that this also answers your question 3.

In general if there is a straight line segment on a drafted plat/plan that:

• connects with a circular arc without an obvious bend where the 2 connect,


• there is no bearing for the curve shown in the curves table, (if there is a curves table)


• there is no bearing shown near the curve itself, or on either of the curve's radial lines, (if radial lines are shown)

�?�then it can be inferred that for this pair of lines the circular curve is "running tangent" to the preceding straight line.

Similarly, if the preceding line is also a circular curve, then you'd have a tangent curve that is running tangent to the preceding circular curve. When you create a tangent curve it is, by definition, never the first line that you enter for a new parcel or for a new construction.

The term "tangent" is also used in a different context, and it can sometimes cause confusion; when referring to a "tangent bearing" for a circular curve this is referring to a property of the curve itself rather than to its tangency with respect to a preceding line. This is more fully described in the video, but the tangent bearing is one of 3 different bearing formats that may be used to define the orientation of a curve with respect to north, and it is not directly related to the concept of a "tangent curve."

Hope this helps.

-Tim

[AndrewThorup]

Thank you Tim and Chris, your answers were very helpful.  I realized what I was doing wrong and I hope my explanation makes sense:
 
When I put an * in the bearing field and entered the radius and arc length, it would automatically populate a chord bearing in the same direction as the previous line (I had the bearing field set to chord bearing).  For example, it would calculate a chord bearing of S56�?30'30"W.  I needed the chord to be pointed in the NE quadrant, so I simply changed the SW to NE, which did not work.  What I did not realize is that I wasn't shifting it 90 degrees like I was supposed to.  N56�?30'30"E is not a 90 degree shift from the same coordinate in the SE quadrant.  When I properly subtracted 56�?30'30" from 90 degrees and entered N33�?29'30"E, the curve took the form of what is showed in the plan.  So it is possible to calculate the radial, chord, or tangent bearing based off of two geometry parameters by placing an * in the bearing field and doing the proper conversion (if required) to the desired quadrant.