Using Map 3D to transform coordinate system.....and data shortcuts?

[Bob_T]

We are starting a project that we will be preparing a site grading plan for.

We are being provided with an ALTA Survey drawing that is on state plane coordinate system, and the existing topography that I will be using for my existing surface is on a UTM coordinate system.

The site grading plan needs to be on state plane coordinate system that the ALTA Survey drawing is on.

I haven't done it before but I understand you can use Map 3D and take drawings that are on different coordinate systems and have them line up properly.

If I have my existing surface in a UTM coordinate system and want to data shortcut it into my site grading plan that's on state plane coordinates, will that work?

Before I spend much time on the project I would like to get some input from people with experience using multiple coordinate systems on a project and how feasible it is.

Thanks in advance!

[thepworth]

Be forwarned that yes, map can transform basic autocad entities from one CS to another, but it doesn't work for AEC objects, such as points, parcels, alignments - just CAD blocks, lines polylines.

Open the mapwspace.  click on the Map Explorer tab (2nd one down) right click on drawings & attach.  THen perform a drawing query on all drawing objects and if the source & destination drawings have assigned CS's then it will transform the autocad objects over easy as pie.  but not yet fully C3D compatible due to the AEC issue.... go figure 😞

[d_reno]

Note also that you have to define the coordinate systems in each drawing before doing the query. I think there may be a setting in the query>drawing dialog that further specifies that a transformation should be done (been a while since I had it open). when you query you set the logical statements to include all (*) objects. you have options to set Draw, Show and one other option - I usually set it to Draw so that the obejcts are in your UTM drawing.

Also, you perform the query from the UTM drawing and you attach the State Plane drawing in the query dialog. when you are done you may want to detach the State Plane drawing since there is a lock put on the file that prevents you from opening it as long as it is attached.

In addition to not querying AEC objects (Use LandXML) a query also won't do vertical transformations in the case that you are going to/from meters and feet. I use a seperate coordinate transformation software when I have that going on.

If you have points in the State Plane drawing you should ask for an Ascii file from the surveyor to avoid hassles.

[Bob_T]

Thanks for the replys.

Looks like one or the other needs to be adjusted to the others coordinate system.

Good times, good times!

[d_reno]

it actually only takes about 5 minutes after you've done it a few times, and is way cool. let us know if you run into problems.

[Bob_T]

Can I trust Map 3D to allow me to accurately line up the 2 coordinate systems, without having a few common points on both coordinate systems to confirm?

[thepworth]

I've seen folks say that they've gotten unexpected results.  but if it's just contour lines for a surface, you really shouldnt be too concerned if it's slightly off

[thepworth]

that is, in the context of an ALTA and not a detailed design grading plan 🙂

[mmcmanus]

  Keep in mind that when you change coordinate systems, there will always be a slight variation in the locations (this varies depending on where you are in the world). A "square" in one coordinate system is not always a "square" in the converted coordinate system.

[d_reno]

ditto to what McManus said. consider also that State plane coordinates usually have a grid to ground conversion factor (you can probably set this in the Map query if you know what it is), and this can affect the results. also, I have noticed anomolies, or errors, in converting to our Wisconsin County Coordinate sytems - this was some time ago and Autodesk was contacted, but never, to my knowledge, fixed it. I found the error by comparing the (then) LDT results with our State sanctioned conversion program results (C3D uses the same conversion routines and coordinate systems as LDT did, if I am not mistaken). the erros were about 0.1' - not enough to really affect grading, but enough to mess up my boundary and PLS survey work.

so the point being that the conversion may be right on the nuts, but it could well be off a little. So yes - do check. if you can convert the coordinates of a couple of points using another method like CORPSCON  (I use WisCON in Wisconsin) to check the results. chances are that there could possibly be a slight shift to correct things after the fact, but that no rotation or scaling will be needed. so as long as you document what you did it is perfectly acceptable to convert using map, run some sort of independant check, adjust as necessary, document for future users, and away you go.

I would still try to get the survey data in Ascii format and run it through CORPSCON or whatever - then you'll have thousands of check points, and can use this data to build your DTM from.

Oh! You might also request a LandXML export of their surface from  their software with the coordinate system defined in it. they're surveyors, they should be able to do that easily. then I am pretty sure C3D importing LandXML files with a defined coordinate system into a drawing with a different defined coordiante system would work to do a coordinate conversions too - on points, surfaces and alignements.

however you get it there, check the results!

[AllenJessup]

Ditto on the Corpcon! That's the only way I transform points!! Export all the point from UTM, convert with Corpscon and Import to a new State Plane drawing. It helps if you have description keys an point groups to get the points back to their layers.

Allen

[Sinc]

---

@Bob_T wrote:

Can I trust Map 3D to allow me to accurately line up the 2 coordinate systems, without having a few common points on both coordinate systems to confirm?

---

NO!

The basic problem is that most people don't understnad what coodinate conversions inolve.  In situations like this, you can't assume ANYTHING.

The only way to be SURE you know things correlate is to have some field observations made, and have some common control points in each system.  Otherwise, you're shooting in the dark.

Neither C3D nor MAP3D actually has provisions to help with this, so you're pretty much on your own...  All I can say is hire a good Survyor who understands this stuff...  Otherwise, you may be liable for the consequences.  If you're lucky, it will be in the .1' or .2' range, and no-one will really care.  At the worst, you can be liable for ?????  I hope you have E&O insurance.

[Bob_T]

Thanks for all the responses. I just wanted to give an update on what we ended up doing.

We checked to see if our client was aware that the ALTA Survey and the topo they were providing to us are on 2 different coordinate systems. For all we knew they may have already done something about converting the 2 drawings to the same coordinate system and inadvertantly provided the wrong files. After being informed about the 2 different coordinate systems our client has instructed the engineering/surveying firm that prepared the ALTA Survey drawing to convert it to UTM Zone 12 coordinate system, the same as the topography they have. (...hopefully they won't just use Map 3D)

I feel all warm and fuzzy inside now!

[Neilw_05]

I may be wrong but I believe converting to a UTM system could result in a larger Grid to Ground scale factor vs. a state plane system as the UTM zones cover larger areas. I would investigate the difference before committing to the UTM system.

[AllenJessup]

I agree with Neil. You need to see what affect that will have on the Survey. I've seen problems following strict ALTA guidelines and producing maps in true State Plane. If you're in an area with a large conversion factor all the Boundary Line distances can change. Angles can change too. Converting to UTM may make these differences even larger. This sets off alarm bells with lawyers who want to roll over the previous description and often do anyway despite revised Survey information.

We usually try to work in a ground system based on a project. Right now I'm lucky to be working for a County where Ground and Grid have very little variance over a few miles.

Allen

[Bob_T]

I'll let you know what happens.

We are also an engineering/surveying firm but we didn't provide the survey for the ALTA or the survey for the topography. We are the company that will be preparing a site grading plan and need to use both and need them both on the same coordinate system. 

When we first got the data for the ALTA and the topo, and saw they are on the 2 different coordinate systems I did some checking and saw the ability of Map 3D to convert from one coordinate system to another, which is maybe good for planning purposes and some other uses but on further investigation would be risky at best to use for construction documents without field verfication, as it has been pointed out in this thread and also discussing with our survey department.

I know which engineering/surveying company prepared the ALTA but I'm not sure who provided the survey for the topography. Since the client is asking the compay that did the ALTA survey to convert to the other coordinate system, as a professional courtesy we can give them a heads up on the possible issues (which they are probably aware of) but it's up to that company to do what is the right thing to do for the client.

[Sinc]

I'm not entirely sure what can happen when you try to transform an ALTA to another coordinate system.  I think it varies, and there are no hard-and-fast rules...  In theory, you should be able to do that, and still maintain the required accuracy, although your bearings are likely to change.

One of the other problems you can run into is that a typical "coordinate system" is usually created on Elevation = Sea Level, and if you are not at sea level, your distances will also be impacted....  For the most part, ALTA surveys should have GROUND distances, not grid.

But in the simplest case, I agree that holding the coordinate system of the ALTA may be the way to go.  Transforming a topo to a different coordinate system usually results in errors that are insignificant for such a thing.  But of course, the other factor is that C3D is VERY BAD at transforming data, and Map can't even see C3D entities, so you can run into all kinds of problems.  And that's not even getting into the ramifications of the "Transformation Tab", which Map also ignores.