Data connect and transformation settings...

[jon]

I have geotif images that I've purchased from Washoe County GIS. They have world files that work great with data connect. That is, as long as I want to work at sea level. We have a Combined Factor mandated by the County for all record maps. it's a simple grid to ground factor. I can set this factor in the drawing settings and import my sea-level coordinate files just fine. The pboblem is that I can't get the Data Connect to work with the transform settings.The problem is the same with Geotif files and SHP files. I've tried using an x-reference drawing to insert the Geotif and then scale up the geotif but the imagery doesn't scale up.

Is it a program bug that keeps Data Connect from recognizing the transformation settings?

[tcorey]

Hey Jon,

What happens if you use MapImport instead of Data Connect?

Tim

[jon]

There's no option for .tfw or .tif files

[tcorey]

Sorry, use I meant Mapiinsert. Two i's.

[jon]

That brings the image into the same place as the Data Connect. Still at sea-level coordinates. The mapiinsert command gave me a dialog box with an optional scale factor. I used the correct one (1.000197939) but it came in exactly where the Data Connect put it. I used the properties box to change the scale factor again. Still no change.

[BrianHailey]

I would recommend posting this over in the Map 3D discussion group. You'll probably get a better response there (not that the responses here are bad, just that those guys specialize in this stuff so there will be more people able to help).

[MATRIX3DSURVEYS]

You cannot bring the image up to surface elevation, without creating a great deal of distortion of the image. There is no simple conversion as the conversion from Grid to ground is dependent on the elevation.  You may be able to use Raster Design to collate small areas with Rubber Sheeting.   (Note: When we collate raw aerial photos to datum, 16 -128 match points are used.)

The other idea is to use a DEM to create a surface and measure 3D poly-lines on the surface. But they may tend to be longer due to following the contour.

Map Projections are based on a Sea Level Datum to give a known consistent spherical surface reference (Geoid).  Scale Factor is a parameter of the map projection to correct for distortion of placing a curved surface on a flat piece of paper. It is a variable that changes dependant on the type of projection and the distance from the origin of the projection.

It appears that the County wants a Surface Ground distance in addition to a Grid Distance (Sea Level)

Ground = GD / SF + C

HD = SD*Sin ZA

Sea Level Grid Distance  GD =  ( (HD * Re) / (Re +( (E1 + E2)/2) ) * SF

or

C = (HD * ((E1 +E2)/2)) / Re

Where :  HD = Horizontal Distance

                GD = Horizontal Distance Sea Level corrected for scale factor

                SD = Slope Distance

                ZA = Zenith Angle

                Re = Radius of Earth = 20925646.33 feet

                E1 = Elevation 1;  E2 = Elevation 2  Elevation at each end of measured line.

                SF = Scale Factor  Dependant on Map projection parameters. (From CORPSCON or C3D point file desplay)

                C   = Correction to Sea Level

A  10000 foot line at 6000 feet would be 9997.13 at Sea level

Jim

Matrix3DSurveys

[jon]

Not the case Jim. I just need a simple scale function. I'm using a combined factor that has been established by the County. The imagery is already orthorectified.