
	Applies To

	Product(s):	gINT Professional
	Version(s):	N/A
	Environment:	N/A
	Area:	Data Entry
	Subarea:
	Original Author:	Kathleen Holcomb, Bentley Technical Support Group

Matching Scale and Origin in Imported Site Maps

When you import a DXF file to use as a site map in your gINT project, you need to make sure both the scale and the origin point of the map matches with borehole locations stored in the gINT project database. The method to correct the scale and origin point in gINT Software’s Drawing application follows.

This method requires that at least two borehole locations used in the gINT project database be marked on the original site map drawing. (If more are marked, choose the two located the greatest distance apart from each other as your “reference” boreholes.)

Recognizing Origin Point Doesn't Match

In exploring this topic, the site map we used was a .DXF file of a boring site, a tank farm, exported from AutoCAD®. DXF files can also be generated from MicroStation® and Visio®.

The initial import of the site map revealed that the origin of the DXF drawing did not match the origin of the East and North coordinates plotted from the gINT data for the boreholes. After tank_farm.dxf was imported in gINT as a site map, the gINT-posted boreholes were not even “on the map.”

Once you realize the site map is not suitable “as is”, you can get rid of the imported .dxf drawing by turning off Site Map Support under Additional Modules.

Correcting the Origin Point

To modify the origin point, we could go back to the original source application, but gINT includes a CAD application (gIDraw), which we can access from the DRAWINGS tab under the General Drawings tab. (Users who have the gINT Logs product will not have a General Drawings tab.)

We imported tank_farm.dxf into DRAWINGS > General Drawings as a new file (which we named DXF SITE MAP).

What We Did to Accomplish This:

Clicked on the Zoom Extent tool. This way, we can be sure we are seeing the whole imported drawing.
Selected all the entities to Move.
Chose the center of the BR-1 borehole point (one of the minimum two boreholes with a position marked on the site map drawing) as the Handle Point by clicking on it.
Entered the East and North coordinates of the BR-1 borehole as the Final Location of the Handle Point by typing them in the coordinate box.
This moved the map drawing so that the BR-1 location marked on it coincided with the position of the BR-1 borehole in the gINT data. If the scale factor had been the same, this would mean that both the site map and the gINT data had the same locations for all boreholes.
Exported the drawing with the shifted origin with a new name: dxf_site_map.dxf by selecting File > Import/Export > DXF Export.

Recognizing Scale Doesn't Match

To test the scale of the drawing with the shifted origin point, I imported dxf_site_map.dxf as the new site map in the INPUT tab.

Now the boreholes were all “on the map”, but only BR-1 coincided with its mark on the site map. The other boring on the site map (We call it AMW-1s to distinguish it from the gINT borehole location marker AMW-1b) to the north and east of the tank farm, is off. The percentage difference between the distance from BR-1 to the AMW-1 on the site map, and to the “AMW-1b” borehole entity marker, is the scale factor for the site map.

We can see we need to scale up because the AMW-1 site map marker is closer to BR-1 than the borehole coordinate marker.

What We Did to Accomplish This:

We used the gINT tool for Distance , located in the lower right corner of the Site Map window, to measure the distance for each:

BR-1 to AMW-1s BR-1 to AMW-1b

Scale Factor Calculation: 323.75 / 318.93 = scale factor of 1.015
We did this five times, because the distances measured can vary with the exact point where youclick.

The average scale factor came out to 1.014.
Since the site map was still not suitable, we turned off Site Map Support under Additional Modules to get rid of dxf_site_map.dxf file as the site map.

Adjusting the DXF Scale in gINT Drawings

We went back into the Drawing application to adjust the scale.

What We Did to Accomplish This:

The Scale Multiply tool (Modify menu) allows us to set a precise scale factor for the site map drawing:
The scale factors for X and Y are adjusted separately, but in this case we want to scale the drawing in proportion, so we used the same scale factor for both. All the other options in Scale Multiply can be left blank.
Once you click OK, you are asked to Select Entities to scale. We selected all the entities on the site map drawing, then clicked the OK button below the drawing area.
Next you are asked to enter the Base Point for scaling. We entered the X,Y coordinates for borehole BR-1 in the coordinate box at the bottom left. (These are now the same as the East, North coordinates from the gINT data.) We could also have clicked on the BR-1 borehole marker, but that would not be as accurate.
We saved the scaled map as dxf_site_map-scaled.dxf, and imported it as the new site map.

Caveats

Scaling accuracy increases with the distance between the two “reference” markers.
Scaling accuracy also increases with the percentage of the map spanned by the distance between the reference markers.
In most cases, point selection by mouse will be less accurate than entering point coordinates in the box.
North and East coordinates will need to be calculated for the requisite two reference boreholes if you are using station and distance along a baseline or latitude, longitude as borehole locations.