Local Mine Grid

[chlang]

I have a large amont of CAD data in several local Mine Grid projections. These Mine Grids can be translated to UTM by rotating around the X,Y and Z axes, applying a false northing and easting and elevation correction, and scaling (not necessarily in that order, and I'm still trying to figure out the order of operations).

Mine Grid to UTM conversion - 7 parameters:

x-translation
y-translation
z-translation
x-rotation
y-rotation
z-rotation
scale factor

I looked at the Local Cartesian Projection in ArcGIS, but it is defined relative to a geographic point (Lat/Long) rather than a Projected point (Easting/Northing) and the parameters for this projection are not well defined in terms of how they should be specified. I had thought that my grid should be based around the x/y/z translation in my 7 parameters, but then what would my false easting and northing be? And can I specify an azimuth that is rotated around all three axes somehow? Or is it that the software can determine the x and y axes rotation automatically when it places the plane tangent to the specified point and all I'm putting in as an Azimuth is the z axis rotation.

Local Cartesian Projection - 6 Parameters:

False Easting
False Northing
Longitude of Center
Latitude of Center
Scale factor
Azimuth

Does this make sense to anyone?

[mkennedy]

I have a large amont of CAD data in several local Mine Grid projections. These Mine Grids can be translated to UTM by rotating around the X,Y and Z axes, applying a false northing and easting and elevation correction, and scaling (not necessarily in that order, and I'm still trying to figure out the order of operations).

Mine Grid to UTM conversion - 7 parameters:

x-translation
y-translation
z-translation
x-rotation
y-rotation
z-rotation
scale factor

I looked at the Local Cartesian Projection in ArcGIS, but it is defined relative to a geographic point (Lat/Long) rather than a Projected point (Easting/Northing) and the parameters for this projection are not well defined in terms of how they should be specified. I had thought that my grid should be based around the x/y/z translation in my 7 parameters, but then what would my false easting and northing be? And can I specify an azimuth that is rotated around all three axes somehow? Or is it that the software can determine the x and y axes rotation automatically when it places the plane tangent to the specified point and all I'm putting in as an Azimuth is the z axis rotation.

Local Cartesian Projection - 6 Parameters:

False Easting
False Northing
Longitude of Center
Latitude of Center
Scale factor
Azimuth

Does this make sense to anyone?

Yes, but I don't think we can emulate it easily. Generally, we're still working in 2D, particularly with the map projections. I haven't really seen a 3D conformal transformation for a local grid before.

There’s no way to really easily build a custom prj file, but it’s often possible. As you've seen, we have a map projection method called “Local” which supports a center point, azimuth, scale factor, and false easting/northing. The azimuth value allows us to incorporate a plane rotation. Another projection that can support similar parameters is RSO (rectified skew orthomorphic). Because these work at the spheroid/ellipsoid level, the parameters you have to convert to/from UTM won’t be directly applicable. If you have any information on the local grid’s center/origin point, that can be used.

The steps are:

1. Create two sets of corresponding point shapefiles: one in local grid, the other in UTM.
2. Make sure the UTM data has its coordinate system defined. Do not define a coordinate system on the grid data.
3. Add both to ArcMap.
4. Open data frame properties and select the coordinate system tab.
5. Create a new, custom projected coordinate system (pcs).
a. Name: anything you want
b. Geographic coordinate system: same as the UTM zone, likely NAD 1983
c. Projection: Local
d. Parameters:
i. Longitude of center/latitude of center: enter if known, if not, try to identify a point near the center of the data or near nice “even” grid coordinates
ii. Scale factor: leave = 1 for now
iii. Azimuth: Try entering the value you have but it’s almost certainly incorrect (that’s because angle is based upon the UTM zone which already has an angle from north)
iv. False easting/northing: if you know the center coordinate, use those values
e. Units: whatever the grid is in
6. OK all dialogs. You will see the UTM data being projected on-the-fly to the new custom pcs. The ‘unknown’ data is just displayed—because ArcMap can’t reproject it.
7. You can now modify/edit the data frame’s coordinate system. Change the azimuth, scale factor, etc. You want to line up the state plane data with the grid data.

You then work back and forth, with change the azimuth/scale (possible origin), then updating the false easting/northing values.

Melita

[seefu]

Here's a tutorial I wrote up for the company I work for.
I found it hard to translate what I wanted to happen towards the end. Probably my brain dying after months and months trying to figure it out.

Hope it helps.

Sandy

Edit: Combine my pictures with what Melita has said to make life easier. She explains it better hehe

Edit 2: I'm a bit late aren't I...

[matt1977]

Hi Melita and Sandy

Would you please explain the steps with images.
Sandy used a good way of explanation but it didn't work for the local points.

Thanks
Matt

[seefu]

Hi Melita and Sandy

Would you please explain the steps with images.
Sandy used a good way of explanation but it didn't work for the local points.

Thanks
Matt

Hi Matt,

Which part have you been having trouble with?

Cheers, Sandy

[matt1977]

First of all I'd like to know how we can convert the local grid to MGA.
Because in your table both local grids and MGAs are available. what if we only got the local grid?

Regarding the procedures you explained, after defining the GDA on the points, I defined the local on the points and exported as a new layer in ArcGIS but didn't appear on the map display I zoomed to the layer and ticked it on and off nothing there but GDA ones.

Cheers
Matt

[seefu]

First of all I'd like to know how we can convert the local grid to MGA.
Because in your table both local grids and MGAs are available. what if we only got the local grid?

Regarding the procedures you explained, after defining the GDA on the points, I defined the local on the points and exported as a new layer in ArcGIS but didn't appear on the map display I zoomed to the layer and ticked it on and off nothing there but GDA ones.

Cheers
Matt

Hey Matt,

I'm assuming you're in Australia if you're using the GDA and MGA systems. You will need to know the real-world coordinates of the Local Grid control points you are using.
My guess as to why your control points in local grid are not showing up is because they have an unknown projection and your current coordinate system. This would make your local grid points show up as Lat/Long in the 1000s or 10000s values which would not show up on a map as that would be off in space or something.

Step one from here would be to find those MGA coordinates for your control points and display those first using the right projection.
This would also help confirm that they're in the right place.

Try follow the tutorial after that and let me know if you have any further problems.

Cheers, Sandy

P.S. For best results, use control points that are further out where the majority of the data will sit in between as the further away you get from the line joining the two control points, the more the projection becomes skewed due to ArcGIS' view of a round earth.

[dhan_sbm]

Hi Sandy, Melita,

We are struggling to follow the instructions in Sandy's notes.
Our surveyors & mine geologists use a two point transformation using the local and MGA in Surpac and it takes them just 3 minutes to convert the data from local to MGA and vice-versa!

However with ArcGIS's interface of creating a new local PCS, it seems to be different and hard.
The information we have for the transformation in the spreadsheet is:
Rotation (clockwise +ve)
Grid Azimuth (Anti-clockwise rotation -ve)
MGA E1
MGA N1
Grid Local E1
Grid Local E2
Scale = 1.0

I have attached the spreadsheet herewith.
Can you please assist in providing step-by-step solution in creating a custom .prj for converting the data from Local to MGA for the attached grid specs?

Thanks heaps.
Dhan

[mkennedy]

Hi,

ArcGIS does support georeferencing CAD data through two points. There are several help topics, starting with this one:

Georeferencing a CAD dataset

If you want to see the surrounding topics or use the installed help, it's in Professional Library, Data Management, Geographic data types, CAD, Managing CAD data.

Melita

[mkennedy]

Hi Dhan,

By the way, which MGA zone is this? Is it 54? (central meridian at 141E)

Thanks,
Melita

[dhan_sbm]

Hi Melita,

Thanks for your reply for georeferencing CAD datasets. However, our query relates to shapefiles.
We wish to bring shapefiles in local projection in ArcMap (based on the custom projection) on the fly to overlay on top of MGA Zone 51 datasets.
The MGA zone is 51 (Kalgoorlie, Leonora, Laverton, etc...)

I can provide you with the 2 point transformation if you would like to have a play around.

[I viewed a demo of the conversion of data from local to MGA & vice-versa in Surpac (3D Mining s/w) and it took only 6 minutes to perform the process!]
However most of our users use ArcGIS and we would like to learn and implement the custom projection in ArcMap.

Thanks for your help.

Best regards,
Dhan

[mkennedy]

Hi Dhan,

I hope that whoever set up the transformation parameters set them up to take advantage of Surpac's capabilities! That method (and the CAD one I mentioned earlier) both occur in 2D space.

I'm trying to solve the problem with a very different type of solution. By trying to define a custom projected coordinate system, I'm trying to emulate the 2D transformation with a 3D to 2D solution. Because of that, I can't use all of the same parameters that are in the Excel spreadsheet or that Surpac is using.

I currently have a custom pcs that has both points offset around .15 m. There's still a rotation, and possibly a scaling that isn't quite being taken into account. I'm going to try to work with it a little more to see if I can fine down the offsets.

If you know the lat/lon of the mine grid's origin (and its xy coords at that location), that would help. I managed to get it this close, by choosing an origin point equidistant from the two control points, by the rotation between the 2 systems isn't exactly symmetric.

Melita

[dhan_sbm]

Hi Melita,
Thanks for your prompt reply. Really appreciate it.
Yes the transform parameters were set up by the Surveyors to use it in Surpac.
0.15 m sounds pretty good I had a difference of more than 50 metres!
I assume the scale is 1.0 or 0.9996
While the rotation is -15.13 from True north (MGA) to Local (backwards) - see attached pdf file.

I have also attached the revised spreadsheet (SOG_for_ESRI.xlsx) with the lat/long equivalent coords for the 2 local points. I cannot figure out which one of them should we use as the grids origin. Or is it the centre of the two points?

In the spreadsheet: MGA is in Zone 51 Leonora; The values of GDA Lat are corresponding and equal to MGA and Local Grid points.
GDA_LAT1 = MGAE1 = GridE 1
GDA_LONG1 = MGAN1 = GridN 1

Similarly,
GDA_LAT2 = MGAE2 = GridE 2
GDA_LONG2 = MGAN2 = GridN 2

The Grid Azimuth is the angle of difference between the Local Grid North and true North MGA starting from Local North (hence -15.13 degrees)
The actual rotation +ve from True MGA North to Local Grid North is 344.52

I am keen to learn about your 'different aspect of resolving' this issue.

Thanks & regards,

Dhan

[mkennedy]

Thanks for the further information!

I'm going to try another round of lining up the points by moving the center. I don't think using one of the control points will work; I think if I nudge the center a little, I can get the rotation working better. In my best attempt so far, the rotation is close to your stated value, but I don't get as good results if I use the grid azimuth value.

So you can see what the current results look like, I'm attaching the prj file as a .txt file (not allowed to attach .prj!). Place in the Coordinate Systems > Projected coordinate systems folder after renaming it. Set ArcMap to use it, and see how the MGA data lines up with the mine grid data.

Melita

[mkennedy]

And here's a new try. I moved the center point to the 2nd point (thanks for the lat/lon values!). Then I could focus on the rotation of the 1st point only. To line up both, I had to also add a small scale factor and modify the xy plane rotation value some more. Both points are very close, but you may find more differences in other areas of the mine.

Melita

[dhan_sbm]

Hi Melita,

Thanks for your efforts in resolving this! The prj file provided by you works absolutely fine on the data while converting between the SOG Local mine to MGA51.
I had selected 'Local' as the projection and it did not work.
Can you please explain why was Rectified_Skew_Orthomorphic_Center chosen as the projection?

The next big task for us is to produce similar .prj files for other local mine grids from where we plan to source our data to be used in ArcGIS. We have around 75 local mine grids out of which we are considering 12 grids to create the .prj files for!

Can you please mail me a detailed document of the procedure you followed in order to make this .prj file work so well? Also if you can provide me an account of tweaks & modifications you had to do to make it aligned with minimal difference, that would be great! This will help me to create the rest .prj files for other local mine grids. My email is: dhanendra.prabhu@stbarbara.com.au
This is certainly contributing to a great learning experience!

Sincerely appreciate your assistance and efforts.

Thanks

Dhan

[mkennedy]

Hi Dhan,

I'm working on a document that's more general than this particular case, although I'll definitely talk about it.

A colleague in technical support, who handles much more of these type of issues (and wrote a book about it: Lining Up Data in ArcGIS) has said for a while that she gets better results with RSO than Local. I had usually done okay with Local.

There are several differences between the two projections, but the main reason the RSO works better is because it supports a planar rotation (XY Plane Rotation) parameter. That is, data is projected to a plane with the map projection algorithm, then you can rotate the plane using that parameter. This more closely matches what happens when someone creates a conformal/similarlity transformation.

In Local, the rotation (azimuth) is more integrated into the map projection so in a sense it's occurring on the ellipsoid. RSO is also conformal, which Local isn't, although the data extent involved in a survey is usually small enough that it shouldn't matter.

Melita

[seefu]

Hey guys,

Sorry for the late response. Have been having some internet issues out here at work (sucks working so remote)

Looks like Melita has it all sorted.

Keep in mind, that with local, the accuracy of the points will decrease the further away you move outside of where the control points are.

I'd like to see how the RSO projection works also.

Cheers, Sandy

[dhan_sbm]

G'day Sandy,
Thanks for your response.
Melita has resolved this problem!
The RSO projection works fine with MGA51 data. I have managed to create another transformation using this method and it appears satisfactory. However if the data is too large, then there may appear differences in the accuracy.

Based on Melita's advise, I have ordered the Esri press publication book "Lining up data in ArcGIS: A guide to map projections" written by Margaret Maher.
I am also waiting to receive a procedure for the methodology followed from Melita.

Take it easy in the bush!
Cheers
Dhan

[mkennedy]

Hi Dhan,

I haven't gotten as far as I wanted on the methodology document--and I'm out of the office for a week starting tomorrow! I won't have access to a work computer, so I'll have to finish it when I return. I'm very sorry.

Melita

[aimong]

has anyone here automated a process like this? We've got thousands of these we need to map. just wondering if it's possible. we just need to have false easting and northings calculated from a top hole, we dont have don't need azimuths or scale factor calculated.

[knewman]

Hello,
Just wondering if it was possible to project the opposite direction so that the local grid is being projected on the fly to the Geographic coordinates?
I got it to work perfectly from UTM to Local grid - thanks for all the instructions above!
Cheers,
Kim

[WarrenMedernach]

Hello all,
I'm curious if this methodology document was ever completed?

Warren M

Hi Dhan,

I haven't gotten as far as I wanted on the methodology document--and I'm out of the office for a week starting tomorrow! I won't have access to a work computer, so I'll have to finish it when I return. I'm very sorry.

Melita

[mkennedy]

Hi Warren,

Willy Lynch wrote a workflow document on this. Please drop me an email and I'll send it to you: mkennedy at esri dot com.

Melita