I have a MrSid image in my base map. The dwg setting is set to UTM survey ft coordinate system.
This image is shifted north approx 30 ft basd on comparison of position with shapefiles imported using Map3D 2010.
I have tried several methods to insert image:
1.Map | Image Insert | insertion units meters
2. xref a dwg with image inserted and drawings units: meters
I think the fundamental problem is that the image is treated like a block and the conversion factor is 3.2808. This works great for internaltional ft units, but not survey feet.
How do I change the default conversion factor to 3.28083333 to more accurately convert units from meters to survey ft?
I think the north shift is more obvious since the northing coordinate is 10x the size of the easting coordinate.
btw....I tried to use Data Connect but with the help of Autodesk help people, but we determined the large file size prevents using this feature. Othewise I would use SPC for drawing coordinate system and the conversion would be handled using proper GIS transformation tools.
a little more investigation shows that CAD uses conversion 0.3048 to convert from meters to feet.
If it used 0.3048006096, the 30 ft shift would be corrected.
I checked this using Image | Insert, viewing insertion coordinates and calculating conversion factor.
How do I set a different conversion value?
Thanks in advance.
Unfortunately, it seems that the conversion you are referring to is hard-coded in the program. I see two change requests related to MAPIINSERT and the way that it translates between units, and I have linked your case to those so that they receive further attention from our developers.
I have done some tests based on your posts, and I wonder if the issue here is the fact that there is no option for International Feet or Survey Feet in the Units drop-down of the MAPIINSERT Image Correlation dialog.
I wonder if the scale be changed from something other than 1:1 to correct this issue? I'm not sure, as I have been unable to reproduce your exact issue. If you want, I can enable a FTP site for you to provide me a complete dataset so that I can observe the issue and maybe provide other tips.
You mentioned using FDO as an alternative to MAPIINSERT, but your challenge was the size of the MrSID image. You can try this on a 64-bit system with at least 8GB RAM for good results, or you can try trimming and/or converting the image to another type. There are some great workflows for doing this in AutoCAD Raster Design, if you have that product - please see the following blog for more information:
I hope this helps you.
what is the coordinate system of the MrSID? What is the resolution of the photo? What is the index point of the photo? Do you need the entire photo for your current project?
your coord system should be such as utm83-(Zone). ie I use utm83-19 in the NE USA. The local NRCS naip photos are either the same or state plane depending on which state. open the corresponing .sdw file. the last two lines are the e & n for the index point for that photo. Usually center of top left pixel. New drawing and set the coord system to the same as the phot, insert the photo. Does that point fall onto the map at the correct coordinates? that may account for your 30 feet of shift against a ground based control point.
Note the abstract from a USDA SID file above a 3.75"x3.75" quarter quad is rectified to +/- 6 meters (19.68 feet) a county mosaic is composed of thousands of DOQQ's which are then compressed in the SID format. At best a large area 1 meter SID has a Hz accuracy of +-10m but probably closer to 20m. A 1 meter DOQQ has 1 meter pixels so the smallest discernible object contains at least 10 pixels. The rectification is to +/-6 meters so the point is somewhere inside a circle that is 12 meters in diameter.
In addition to this every time the image is re-projected more distortion is added.
Would suggest the following work flow.
Check the Meta data for the SID. Create a Drawing in that coordinate system. UTM 83-10 meters. Insert the SID with Raster Design.
Image > Insert >Insertion Dialog > Open >Source >World File Correlation > Apply > OK
Save and Close the Drawing.
As a location check Create a Drawing in UTM 27-10 meters and import a DRG Topographic map with the collars. Set the system variable GEOLATLONGFORMAT to 1 (DMS) Set Drawing coordinates in lower left hand corner to Geographic. Check the coordinates of the corners of the topo.
Create a new drawing in required project coordinate system UTM83-10F feet or local State Plane Coordinate System. (Toolspace>Settings Tab> Drawing Settings)
Go to Task Pane > Map Explorer > Attach Drawing with image file. Click current drawing and set coordinate systems for both current drawing and source drawing.
Define Query > Query (ALL/Layer) > Draw
Repeat above steps to import the Topographic map. Set transparency and check against Aerial photo. Check Geographic Coordinates of corners.
Detach the Source Drawings and save the New Work Drawing.
This method does not corrupt the source image file or rewrite the correlation files.
If more accurate correlation is required the photo can be matched to Surveyed Hard points using Match and Rubber Sheet commands on the Raster tools menu. This is how the original Images were Correlated in the first place.
Remember GIS stands for GUESS INSTEAD of SURVEY.
Mapiinsert frustrated me to the point that I wrote a lisp program to insert images instead... see attached. This works for TIF images, not sure if SID images are different. You will need to revise the program obviously to fit your directories and images, but this solved the problem for me.
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