Polymask problem

[Thai1On]

I am trying to prepare a historic raster map using the Polymask tool. I first did Reduce Image, next cropped the edges, next used the polygon mask tool to pick the edges of the map. When I click the polygon tool again I do not get a message box asking for
confirmation to apply transparency? Also the raster map I'm using is not tilted.

Dave

[geophil]

When I click the polygon tool again I do not get a message box asking for
confirmation to apply transparency?

I think it's automatic. Once you have completed the georefencing points and click "Convert to UTM", the polygon mask will be applied during the conversion.

(With a USGS GeoPDF source, where TransDEM recognizes the projection, you don't enter georeferencing points, of course, and go straight to "Convert to UTM" after clicking the polygon mask tool the second time - and the margin has become semi-transparent.)

The behavior may been slightly different in earlier versions of TransDEM, but I am not sure.

[Thai1On]

OK from the USGS should I use GeoTiff or GeoPDF?

[geophil]

You have to try, I'd go for GeoPDF first. For several years it was the only option for raster maps anyway. The GeoPDF format has the advantage that it can incorporate the so-called "neat lines" which then become the pre-set for the TransDEM margin mask. I don't think GeoTIFF can do that. But GeoPDF is slower to read, because it's two-pass procedure.