How does adersheet work?

[dvertz]

I recently discovered this was incorporated into Autocad. Yesterday I needed to use it. But the result was not what I expected. I didn't have time to research what I might have done wrong then, but today I have attempted a few different tries. I used 5 points to stretch the image. Can someone please confirm my suspicion?

It appears to me that it does not actually rubber sheet the image, but rather skews the image making it a parallelogram. What could I have done wrong if this is not the case?

[ChicagoLooper]

Hi @dvertz 

FYI, I have used ADERSHEET multiple times and hate it. I quit using it a long time ago.

Can you upload screenshots? Show the 'object' you're trying to rubber sheet, how it's being skewed, and the parts where it's not consistent with your target points. Is your object an xref? Or is it an image? Or something else?

Using ALIGN command in combination with BLOCK works better. I say that as someone who's used alternate ways to line up and inserted object(s) to an existing map and not one who's been conned  into believing AderSheet's overrated considerations.

[dvertz]

I have trouble getting screenshots to upload but I'll give it a shot.

In the below shot, I have aligned the image (yes it is a JPG image) to the two corners along the road. As you can see the far left is way out of place.

Now, this screenshot it's after I applied the ADERSHEET using the number point 1-7 in a clockwise direction. Notice points 4-6 are still not on their selected corners and that the size of the image is skewed instead of rubber sheeted. A true rubbersheet would have all sides at different distances and all angles different.

[Pointdump]

Hi David,
Cartographers use a minimum of 9 points to geo-reference a scanned paper map. It's been a while since I last tried ADERSHEET, but I also found it a bit lacking. The free >>>MapWindow<<< and QGIS are much better at this.
Dave

[ChicagoLooper]

Hi @dvertz 

OK. I see. I've done that many times and I can tell you with 100% confidence, your efforts to 'line up' will always be off. Why? Because that survey is wrinkled and that wrinkledness won't allow the property boundary (black pixels) in your image to be accurate.  

You are dealing with parcel boundaries in the USA and that's public information. Many Counties in many States offer downloadable parcel outlines to the public free of charge and the county of your site, Norfolk County, is no exception. It offers parcel data that can be downloaded in shapefile format.

Attached you'll find a portion of the parcel shapefile for Norfolk County. I say portion because it only zeros-in on your specific area of the neighborhood, not the entire County. To get the parcels in a drawing, I'd suggest opening a new, brand new drawing first, adding the boundary or boundaries, then cutting-and-pasting from that new drawing into your working file.

The attached file is a zipped shapefile NOT DWG!!! Unzipped the folder first. To use it in a workflow applicable to Map3D, do this: 

1. Open a clean, brand new drawing. Use MAPCSASSIGN and assign the State Plane and zone as shown in image-1.

Image-1

2. Use the MAPIMPORT command to import the shp that's contained in the unzipped folder. (Do NOT edit, add or delete contents contained in the unzipped folder--keep it as is. Be sure to Create Object Data. Grab ALL data that's in the shapefile's database even if you don't plan to use it. <<It's better to have it than not have it.>>

Image-2

3. Zoom extents to view. Don't forget, modelspace is accurately GEOREFERENCED to Virginia state Plane, NAD83, South Zone, feet. In the Layer Properties Manger you may change the layer to orange. The red arrow shows your parcel, correct? If you turn on Bing Hybrid you can use the aerial imagery as a basemap.

Image-3

4. When zoomed-in, your site is this. You may now cut-and-paste from this temporary drawing to your working drawing. 

Image-4

[dvertz]

What a shame. You went to an awful lot of trouble for things I already know. I have been working in the City of Virginia Beach, City of Norfolk and City of Chesapeake for 30 years. I have all the data (and I mean ALL) the cities have made available. I was NOT doing any of this for the parcel data. I was aligning the parcel to the Plated parcel lines (yes I have all the plats too) to trace the house and concrete to measure some areas. Yes. I am very aware of state plane and that geomaps can be used to trace existing conditions. But sometimes those nasty little things with leaves covers the site.

The question still remains. Does ADERSHEET use all the points to rubbersheet, or does it just stretch and skew the image to a best fit? Almost the same as the Align command (which only stretches and scales the image).

[ChicagoLooper]

I would never use ADERSHEET even though I can tell you already want to use it because you've never used it before and think your new discovery is the answer to ALL answers when inserting images......

I would do this:

1. Make a BLOCK with exactly one object which would be the scanned image. When making the block I would NOT check the box named Scale Uniformly. Checking that box will screw things up. Be sure to pick a strategically located base point for this new block--this may require some thought that takes more than 8 seconds.
2. Then, I'd use ALIGN command, not ADERSHEET, to align the longest parcel segment in the image to your target points.
3. Then I'd scale the block, which is the image, in the properties palette and because I intentionally didn't check Scale Uniformly I can scale the image in X direction without any proportional scale in the Y direction, and vice versa. IOW, the X-and Y-scales are independent of one another.

The above workflow, when used by experienced users, will make your image closer to what you want when compared to ADERSHEET.

To answer your question, Rubber Sheet, aka ADERSHEET, will align one, possible two points. Anything beyond 2 is an approximation of where points should land. The command shouldn't be named ADERSHEET, it should be renamed Get-your-image-close-enough-but-not-exactly-like-you-want-sheet.  

[ChicagoLooper]

@dvertz wrote

<<... Yes. I am very aware of state plane and that geomaps can be used to trace existing conditions. But sometimes those nasty little things with leaves covers the site...>>

When using MAPIMPORT command on a shapefile, you are NOT tracing anything, not using a downloaded image. You're letting Map3D add vectors (linework from shapefile format). The tracing you allude to should NOT be part of your MapImport procedure. If your parcel boundary is being traced manually, then you're not utilizing the MapImport procedure in a way that benefits you.

Once MapImport automatically drops the parcels where they should land, you can leverage the parcel's vertex locations and manually re-create (or image trace) the building footprint and 'everything else' with greater accuracy. A poorly drawn boundary results in poorly drawn everything else. 

FYI, you can't re-produce that survey with 100% accuracy using a wrinkled, scanned image. If you could, then you'd put a big portion of surveying firms out of business. All you really want to do is get your parcel boundary as close as possible with discrepancies virtually invisible to the naked eye. ADERSHEET plays just a small role in achieving your goal, and in case you didn't know, it doesn't care how many years you've been working with the City.   

[dvertz · Accepted solution]

Thank you all for your suggestions.

There has been much confusion on this topic. First, the post was moved from Autocad Forum to the Map 3D Forum without me realizing that had been done. It would have clarified that it was a MAP command. Second, ChicagoLooper was correct in assuming that I had found a new command and wanted to use it. I had discovered this command when reading about something else and thought it was meant to do the same thing as IRSHEET in Raster Design. So in the attempt to use it, I was not getting the expected results. That's why I wanted to know "how it worked". But I think I was not clear in my question, as I never got the answer (either way). I wanted to know the underlying code of how it worked to stretch the image into place. Would it use all points and stretch the pixels to fit ALL points. Not just how to use the command.

As it turns out, I found in an Autocad Help file with more information about the command. It explained that IRSHEET is a raster design command that works with raster images and that ADERSHEET is a MAP 3D command that works with vector objects. That means ADERSHEET was never designed to be used on images.

[Pointdump]

David,
I usually use IRSHEET in the Raster Tools, or QGIS, to warp an image, but ADERSHEET definitely does work on images. Here is a Tiff I used just now to warp to 4 points.
Dave