ADERSHEET vs IRSHEET

[GPSJane]

Can anyone explain the difference between ADERSHEET and IRSHEET?

I can't understand why there are 2 different rubber sheet commands and no where on the Autodesk site are the 2 mentioned together or does anyone explain the difference.

[parkr4st · Accepted solution]

  From the help files ADERSHEET (Rubber Sheet command)  works with objects

Use this command to get two or more data sets from different sources to align geographically: for example, when stretching a new subdivision map into a preexisting parcel map.

irsheet

Rubbersheeting an Image   is a raster command

You can transform an image to correct distortions in distance and shape.  Rubbersheeting uses a set of matched control points, consisting of source points in the image and destination points in the drawing. You can specify these points by picking them directly in the drawing, or by establishing a grid of destination points, to which you match source points. Once these control points are established, the image is transformed so that the points align as closely as possible.

what are you trying to accomplish?

[GPSJane]

Thanks 🙂 I get it.

I am generally georeferencing images for digitising and will IRSHEET from now on. Although, I have been using ADERSHEET because I read somewhere it was better (but not why).

It is also useful to know how to rubber sheet data sets that don't match. How much of an error will you end up with though? You could seriously distort data if you're not careful.

We have sets of data digitised from adjacent plans that don't overlay, or only overlay a little, and that often don't meet up at the edges for various reasons. I would maybe ADERSHEET these but this could then hide the fact that someone drew things badly on the plan or georeferenced badly before digitising.

[parkr4st]

you have to decide and balance between precision, accuracy, and a pretty picture depending on your audience

precision is how good the instrument it  

accuracy is how good you are using the instrument

and a pretty picture conveys your mesage to the audience to make them believe you.

this all relative to the size of the area you are working.  WGS 84 CRS for all of Europe may be accurate enough, but if you are mapping 40 square KM it may be better to use a more local CRS to achieve better accuracy.  This has to do with level of detail also.  Country outlines of a continent are good enough to get me to a country there from here, but not to your town. 

so if your base map data is not precise, you can't accurately rubber sheet any better than that precision.  and if the audience doesn't know

how inaccurate the data is placed but believes you, you are succesful.

I recently mapped property parcels for the town I live in.  Surveyors gave me a dwg of the town line on state plane to 5 decimal places.  good precision and accurate.  any survey with a coordinate for a corner on state plane is accurately placed and with decent precison. I typed in metes and bounds off alot of older surveys, lousy precision with fair accuracy so snapped for accuracy to the state plane located survey points on abutting lots.  And fudged the rest of the properties in between all of the surveyed lots,  good accuracy, very poor precision, but all looks good a 1:100000 to anybody that doesn't know the difference.  I drew road center lines from georeferenced 6 inch pixel photos, so-so accuracy and certainly not precise, but the picture is worth a thousand words.  Zoom in and the audience starts to see discrepancies and you don't look so smart after all.

dave

[GPSJane]

I am using hand-drawn survey plans from a mine to create 3D models of the mine and ore bodies. The precision of the plans is terrible and the accuracy of edits is often too but I try to keep their original data and not make up my own, better-fitting lines. Unfortunatley the pretty picture is not important so much as getting grades in the right places. Of course, though, the models must make sense; parts of an underground level must meet up so I end up fudging lines there anyway.

I try to keep the data integrous with what I am given and hope its good enough!

[GPSJane]

I just tried using ADERSHEET on some plines and lines and I can tell you it all went to hell. lines all over in weird places doubling back on themselves etc. This is not that easy and I am not sure how it should be used!

[parkr4st]

maybe you didn't go around in the points in CW or CCW order?  and/or did not use enough points?  It is not the most agreeable command in ACad somedays. 

This help gives good information and videos.

http://docs.autodesk.com/MAP/2010/ENU/AutoCAD%20Map%203D%202010%20User%20Documentation/HTML%20Help/i...

Another possiblity is that your base survey points are not accurate.

If you can post an item that needs to be rearranged and base points others can give it a try?

dave