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GeoTIFF files

 

A GeoTIFF file is a TIFF file that has geographical information attached to it. Scan2CAD uses the following GeoTIFF information:

Geo Tagged information:

ModelTiepointTag

ModelPixelScaleTag

Geo Keyed information:

GTRasterTypeGeoKey : RasterPixellsArea

 

When you load a GeoTIFF file into Scan2CAD and then save it, only the information used by Scan2CAD is saved. This means that any other GeoTIFF information that was stored in the original GeoTIFF file is lost. To prevent this, use File Menu > Raster > Save As to save the GeoTIFF file under a new name.

 

View and edit GeoTIFF information

Create a GeoTIFF file

 

View and edit GeoTIFF information

Access the Vector Scale Settings dialog by selecting File Menu > Vector > Scale Options.

 

If you have loaded a GeoTIFF file into Scan2CAD, the Geo option at the bottom left of the dialog will be selected.

The following GeoTIFF information is shown in the dialog.

Geo Pixel Scale

The distance that each pixel in the raster image represents on the ground.

For example, if 1 inch on a map you have scanned represents 100 inches on the ground in the X (horizontal) direction, and you scanned the map at a resolution of 300 dpi (dots per inch), then the distance represented by each pixel in the horizontal direction will be 100 / 300 = 0.3333333.

Tie Point – Raster Coordinate

This is the raster coordinate location of a known point.

For example, suppose you are vectorizing a map and a known point at coordinate 500,1000 on the raster image is at coordinate 10235,78653 on the map. The Raster Coordinate is the coordinate location 500,1000 (X=500,Y=1000).

Tie Point – Vector Coordinate

This is the real world coordinate location of a known point.

For example, suppose you are vectorizing a map and a known point at coordinate 500,1000 on the  raster image is at coordinate 10235,78653 on the map. The Vector Coordinate is the coordinate location 10235,78653 (X=10235,Y=78653).

 

Often when you receive a GeoTIFF file the Raster Coordinate will have defaulted to the raster coordinate 0,0 at the top left corner of the raster image. This point may or may not correspond to the Vector Coordinate.

If the Raster Coordinate does not correspond to the Vector Coordinate you can correct it as follows:

1. Click on the Select button in the Tie Point part of the Vector Scale Settings dialog.
2. Click on the point on the raster image that corresponds to the Vector Coordinate.

 

Create a GeoTIFF file

1. Access the Vector Scale Settings dialog by selecting File Menu > Vector > Scale Options.
2. Click on the Geo option.
3. Calculate the distance that each pixel represents in the X and Y directions and enter these figures into the Geo Pixel Scale X and Y boxes (the X and Y scaling factors will usually be the same).

For example, if 1 inch on a map you have scanned represents 100 inches on the ground in the X (horizontal) direction, and you scanned the map at a resolution of 300 dpi (dots per inch), then the distance represented by each pixel in the horizontal direction will be 100 / 300 = 0.3333333.

4. Click on the Select button in the Tie Point part of the dialog.

The dialog disappears.

5. Click on a point on the raster image that corresponds to a known coordinate.

The dialog reappears and the raster coordinate of the point you clicked on is automatically entered into the Raster Coordinate X and Y boxes.

6. Type the corresponding known coordinate into the Vector Coordinate X and Y boxes.
7. Click OK to exit the Vector Scale Settings dialog.
8. Select File Menu > Raster > Save As.
9. Use the Save as Type section of the dialog to select any TIFF format.
10. Type a name for the file into the File Name section of the dialog.
11. Click Save.

The Geo Pixel Scale, Raster Coordinate and Vector Coordinate values are saved within the TIFF file.

 

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