Boundary Survey - Bearing Variations

[DINK_R8]

So I have set up a new drawing, selected the state plain for the region.  I have a survey for a plat, though when I enter in the segments using C3D "Create Line by Bearing" I have slight variations between what they survey bearings call out and what would appear to be the actual bearing directions based on the map image easement clearing for say utilities or roads...etc.  I'm not saying that the easements and roads are definitive, but lengths of 1000's of feet can show such variances pretty easily, enough to question if I need to make a settings adjustment.  I wouldn't think I would need to, but it does stands out...  Should I be setting the "direction" within the "drawing units" setup???

See image:

[jefflambert9091]

Your first step is to decide what system you want to be in. Do you want to rotate the survey plat into state plane or vice versa.

We keep everything in state plane. We shoot our control in with GPS/VRS and stay there. Many advantages. No confusion on field work coming in and out and you can bring in all GIS info directly just to name the main ones. You can reference the survey plat bearings if need be. You can type them in manually or figure the angle and write an expression to use with a line label style.

If you want to stay with the survey plat, you can use the transformation tab to get all the fieldwork moved and rotated or use the Translate Survey Database in the Survey Database.  If you do this then you need to move any Images or info that was in state plane. I have gone back in forth with taking state plane info and using the transformation tab to get to an assumed 5000,5000 system, but it just causes confusion somewhere down the line. 

I will always suggest you stay in State Plane.  Especially these days where there is so much information available like FEMA, USGS and all State/County/City info.  

[DINK_R8]

Hi Jeff,

Yes for me staying in state plain would be preferred, for the exact reasons you mentioned...I have FEMA maps and county plat data in the file and they orient just fine...  For example the boundary clip surface in the image was bounded by the county parcel shp file...  That lines up just as expected, though the parcel from the survey is rotated a bit as shown...  So this is normal?  I'm a bit new to civil so still trying to find my way around this...

So is there some reference on what the rotation angle is?  I have the the county shp file in there that can be used quite easily to simple rotate, but then the plat boundary's and everything else drawn with respect to the "rotated" survey will have bearings off but a fixed amount.  How can that be backed out of the labels to correct the rotation so prints show the true bearings?

[rl_jackson]

Most likely your legal description comes from a description that was on a different bearing basis the was most likely the north line of the section being due east. If you have the section monuments you can do the breakdown of the property based on the original intent of the description, this is quite common as older aliquoit description were usually described base on a line being in a true cardinal direction.

[jefflambert9091]

First, I create and abstract layer and put it the survey plat info and then create a block out of it. I do this out to the side of the project out of the way of any plotting. I then copy that block, decide on a point and line to hold on the County Parcel lines. The reason for the block is to maintain the original bearing system of the plat.  Keep in mind that a GIS tech had to draw the property lines the best he could based upon the aerial info. We typically don't label bearings at this point of the project. Maybe some +/- distances. You won't know the exact place and rotation until the the boundary is resolved by the fieldwork and what monumentation the surveyor decides to hold. Once you have that you can do the math from the resolved bearing to the plat bearing to get your angle.   

Be careful with the phrase "True Bearings". Do you mean plat bearings or State plane bearings? 

[_Hathaway]

The bearing you entered was presumably from another map or exhibit or legal.  If you do not know the basis of bearing associated with that line/project/map the line will most likely not match the real world.  Before GIS and state plane coordinates no one really cared.  Nowadays its to your and everyone's best interest to work in State Plane Coordinates.

Does your county have a GIS system available for download? That is what we use as a rough starting point if we have nothing else to go on.  What i am saying is that you should contact your county and see if they have a .SHP file or the parcels within the county.  You can import them to Civil3d using the Mapimport command for a decent starting point for your linework.  Not all county data are created equal, some are very good and some are very very poor.

[DINK_R8]

I have no idea on the basis of bearing for the survey data...  The only survey data I have is from a trust deed file which gets me from a known monument, but does not align with the state plain as you guys already know...

Yes the county does have GIS data, in fact the yellow bounded box in the image (which is my surface boundary line) is in fact the county shp file.  It's pretty decent but slight variances on distance.  I've rotated other "survey" that were just for my reference, but I wanted to find out if I was missing something....

So if I understand correctly, given that I have county GIS data. I can do the following to align the "survey" data to the state plane:

1. connect the county GIS parcel shp file to the drawing.
2. Layout the surveyed parcel per the survey, even though it's rotation is off.
3. Once survey is in, I usually will convert to polyline and join to lock it all together.
4. Rotate the joined parcel to line up with the GIS shp file.

At this point the newly rotated parcel will associate the bearings to the state plain as they off by 1.XX° give or take.  So I don't need to be fixated on the variance between the two now?

Thanks for everyones help...that was bugging me..

[Pointdump]

Chad,

OK, I gotta ask. Are you doing preliminary design work for a building pad or a driveway or ...?

Dave

[DINK_R8]

Dave,

Yes, driveway, pads, utilities...etc...  nothing exotic or anything...

Chad