Set up ground coordinate system in Trimble Access

squowse, post: 354538, member: 7109 wrote: Bit rushed on this one and don't have the controller in front of me.

There is an existing co-ordinate system on the site. It is based on our national grid OSGB36 (via OSTN02 projection). Scale factor at our site is 0.9996

BUT they have used ground co-ordinates. They have specified the "scaling point" in grid co-ordinates. So at that point the grid co-ordinates are the same as the ground coordinates. As you move further away from that point the ground coordinates will gradually diverge from the grid coordinates.

Can anyone confirm if I can set this up in Access easily? I think it is a case of choosing the grid projection, ticking ground coordinates and then supplying it the origin or scaling point? Please let me know the exact menu choices if possible. A screenshot would be ideal. I will have to talk a colleague through it in the morning. As I say I don't have a controller in front of me.

Thanks a million if anyone can advise.

Can I supply the scaling point in grid co-ords or does it need to be in lat/long?
The site is a few hundred metres across.

Perhaps the thing to do is to set up a custom projection zone, which is easy to do in Access, and indeed almost all modern dc software. You would need the lat/long and the project coordinate for a point which would be your grid origin.

If not that you could set up a localization for the project - also a common task.

Going from memory yes you can do it, the only challenge is that the 0,0 point must be entered as a geographic coordinate. Otherwise it is exactly as you described.

Mark Mayer, post: 354564, member: 424 wrote: Perhaps the thing to do is to set up a custom projection zone, which is easy to do in Access, and indeed almost all modern dc software. You would need the lat/long and the project coordinate for a point which would be your grid origin.

If not that you could set up a localization for the project - also a common task.

yes, good idea. I think I know how to do that. I put the grid coordinate in as a false easting and northing.

geopro_consultants, post: 354568, member: 9959 wrote: Going from memory yes you can do it, the only challenge is that the 0,0 point must be entered as a geographic coordinate. Otherwise it is exactly as you described.

Thanks, so maybe I can key in the point to memory. Then call it up in the ground coordinates options.

The local co ord system north is definitely the same as OS grid north?

Got caught by this once, the local system had been rotated from OS grid north to coincide with true north to suit the architect working on a housing layout and 'solar gain' calcs. The difference in direction was trivial in solar terms, not trivial for setting out though. Unfortunately the rotation never got recorded in print that I saw. Picked it up early on when setting out boundary points which were displaced from features on the ground they were to tie in to.

Yep the topo drawing does state the basis of coordinates adequately. I can see that the designer hasn't rotated the topo on his drawing. (although he has scaled it to mm and moved it of course)

squowse, post: 354559, member: 7109 wrote: Can I supply the scaling point in grid co-ords or does it need to be in lat/long?
The site is a few hundred metres across.

use the local site

squowse, post: 354592, member: 7109 wrote: Yep the topo drawing does state the basis of coordinates adequately. I can see that the designer hasn't rotated the topo on his drawing. (although he has scaled it to mm and moved it of course)

squowse, post: 354538, member: 7109 wrote: Bit rushed on this one and don't have the controller in front of me.

There is an existing co-ordinate system on the site. It is based on our national grid OSGB36 (via OSTN02 projection). Scale factor at our site is 0.9996

BUT they have used ground co-ordinates. They have specified the "scaling point" in grid co-ordinates. So at that point the grid co-ordinates are the same as the ground coordinates. As you move further away from that point the ground coordinates will gradually diverge from the grid coordinates.

Can anyone confirm if I can set this up in Access easily? I think it is a case of choosing the grid projection, ticking ground coordinates and then supplying it the origin or scaling point? Please let me know the exact menu choices if possible. A screenshot would be ideal. I will have to talk a colleague through it in the morning. As I say I don't have a controller in front of me.

Thanks a million if anyone can advise.

In Project Explorer under Project Settings go to Coordinate System

Set up the project with the projection as if it was on the national gird

Then simply go to Local Site under coordinate system

It allows you to set the project location, you can do it as a NE or LAT, Long, also imput an elevation or height-they gave you the number for the project location, use a "close" number for an elevation, it really doesn't matter, but I always try to get within 100' of a real number.

Then there is a ground coordinate section which will allow you to put in a scale factor, it will calculate one from the project location and elevation that you imputed, but that of course only applies to the one point in space, you want a project scale factor that is given to you so swipe it and type in the given number.

So instead of using the calculated one use the given one of .9996, also you need to imput it as the inverse, or 1.000400

you can put it at 1.00040016 if you want but since the project point is on site, it's really not an issue to carry it that far unless this site is more than 20-30 miles across.

I'm looking at this in TBC, I never do it in the data collector, this should be taken care of before boots hit the ground, I don't have a data collector here to look at, but I presume all can be done in it, I don't advise doing that however, do it in the office if you can.