Geolocation scale issue

K_Lecky1

New to Brics CAD and having an issue with setting a geolocation..

I received a drawing that has no GPS location markers on it but are reference markers. When these reference markers are put into a grid checker online (numerical values) they are correct.

When I try to set a geolocation (TM75, Irish grid) the scale is off majorly. The first point is correct (on the North East Irish coast, and when I reference it to the next marker (should only be a few metres away) it ends up in Scotland which is a few hundred miles away..

The original drawing in DSETTINGS 'Insertion units' is set at [0] unspecified, yet all dimensions on the drawing are correct in mm.

Anyone any idea why the scale is off so much?

Terry Dotson

There are NO (zero) valid coordinate systems in MM (millimeters) !!!

Beware the GeographicLocation command, regardless of CAD engines. In the case of BricsCAD, turn on the second toggle ([x] Use Map Grid Coordinate System) and choose a system. Any use of the lower section is a recipe for GeoGarbage. In true GeoLocation you DO NOT get to pick a point in your drawing, your drawing is either in the proper coordinates (feet or meters only) or it's not. Failure to properly position drawing geometry on the proper coordinates means you will NOT be able to import properly positioned content, nor will your exported geometry show up in the proper location on exports.

K_Lecky1

Sorry if it came across the wrong way, the co-ordinates are not in mm, they are the actual co-ordinate values according to TM75, they just aren't set as usable gps locations, just 'marks on a page' kind of thing.

The mm I referred to are the dimensions on the drawing itself, of wall lengths etc. and they are to scale.

When I put in the co-ordinate system I need to use (TM75) the Brics co-ordinates (that show in the properties panel as X, Y and Z, when you select a marker) are off majorly.

This is an architects drawing that has 'final product' will be used for GPS guided excavators.

Terry Dotson

Note that there are likely more architects drawings that are NOT properly GeoLocated than any other discipline. No offense to architects, but they are not surveyors / geologists nor would they approve of a surveyor designing a building.

If you check a known distance in your drawing and the value is not a valid distance in METERS, then you are on the wrong track.

If your building drawing happens to be rotated perfectly to horizontal, you are likely on the wrong track (unless the building was staked out (or to be staked out) to be truly north oriented, not likely).

If your drawing coordinates are small, you are likely on the wrong track.

Save and backup your drawing, erase irrelevant portions and SaveAs something like 4FORUM.dwg and post it. If there are any street labels include them, and consider providing the address / location.

zoomer

Note that there are likely more architects drawings that are NOT properly GeoLocated than any other discipline.

Likely true.

I am meanwhile able to geolocate my drawings in Vectorworks.
And AFAIR if I export a DWG to Bricscad it is kept.

I think @K_Lecky1 wants to work in geolocated coordinates (?)

This is not what I want.
From an architectural view I want my working coordinate center at the starting point
of my Building Grid 0/0/0 and my drawing aligned/rotated to the grid.
I also have to do with, or better hope, for getting a reference point with known
world coordinates and best including the projection standard.

I just want the georeference info and north angles saved correctly in my file for IFC or
other applicable exports, while 3D Exports to Apps like e.g. Blender should stay
centered on drawing center.

So could you say in a few words how to setup the georeferencing for this purpose
in Bricscad ?

ALANH

Like others we would get a dwg in mm and asked to set it out in real world co-ordinates. So scaled to metres, then would find 2 reference points and use Align to move the whole dwg to correct world co-ordinates, wont go into local scale required. Think Helmert transformation.

You can set a UCS just draw a line with start point as your desired 0,0 and the angle required, then just do UCS OB, PLAN, UCS save yourucsname. So can flip between world and your UCS.

So you will draft horizontal etc but setout at any time is UCS W then real world co-ords will apply.

K_Lecky1

Thanks for all the replies.

All construction drawings here (Northern Ireland) are in mm and the buildings are orientated correctly (not all horizontally etc) and has a refernce to north on the site drawing.

I've discovered that the scale of the drawing is off by 1000… changing the drawing units under DSETTINGS has no effect on the scaling which I don't understand. I thought that if it was set as mm it would automatically detect that '600' is 600mm and not 600m.

If I scale the drawing by 0.001 the co-ordinate markings line up perfectly. The only issue then is that I have to input metres as millimetres, so if a level is 49.50m on the Z axis, this has to be entered as 49.50mm and everything is in the correct place although scaling is off.

Terry Dotson

IMO the best approach is to leave the building drawing alone, instead begin a new plan/location drawing in meters, assign the coordinate system and determine the proper location and orientation of the building. Then XREF attach the building drawing and the CAD engine should take care of the scaling if both drawings are assigned the correct units. When you are in the building drawing think in MM, when in the location plan drawing think in terms of meters.

A surveyor can help you establish the correct coordinates of the building (especially if it exists). I have seen way too many drawings that the (armchair surveyor) creators called properly geolocated, when in fact they are an untrustworthy mess.