Need Help with Geo-referencing of Raster with Bentley Descartes

Hi Dipson,

If your raster contains no geo-reference information it can be easily referenced by the creating manually a world file for the raster or by placing the raster at the right position with the standard move/scale/rotate tools.

Some information about world file and the geo-referencing process can be found on the following Wiki page : communities.bentley.com/.../raster-reprojection.aspx.

Once the image is located correctly (i.e. : geo-referenced) there will be not need to locate the vectors created by the vectorization process (i.e. : the vectors created by the vectorization process are matching the original vectorized image data, so if the image data is at the correct location, the vectors created will also be at the correct location).

Note that you may want to reproject your image from a latitude/longitude based coordinate to a planar coordinate but note that some tools won't work correctly when the image is reprojected, so it it might be better to do a physical reprojection, which is a simple save as operation of a source image to which a reprojection is applied (see the To permanently Re-project an image section on communities.bentley.com/.../reprojecting-images-to-a-different-gcs.aspx).

Finally if you have the multiple pair of tie points you can register your image using Bentley Descartes registration tools. This process is a bit more complicated though but lead to greater accuracy.

Thanks,

Mathieu

hi Mathieu,

 Cld hav replied ealier, but my internet had some slight prob... Really appreciate ur reply......it went along way in making me understand it better.....especially after readin the  wiki pages and ur advice.

Mathieu, i still hav a prob trying to georeference the raster and still confused on the procedure to use  as am still nt sure hw to create the world file sister file to use in georeferencing the raster. The raster contains nothings and eastings  and was plannin to use it georeference the image.

Pls Mathieu, i hav attached the raster(JPG version cos of size) to this post so u cld tell me hw u wld georeference the raster and the exact steps u wld take.

i believe, wit u practically telling me the steps to take, i would get the georeferencing procedures once and for all.

thanks a lot....

dipson

and also

the image has some known points i.e distance in metres,   and plannin to use these list of known point to georeference the raster.....hw do u think i can go about it.

i tried using macrostation to georeference (using the define frm placemark) , i realized dats it was the design file i georeferenced not the image making the image not correctly placed

the problem am having is that to register and image wit descartes,  i must use a already corrected/ georeferenced image to register it. but am lookin for a way to georeference the image 1st of all

thank you 4 ur help

regards

Hi,

You don't absolutely need an already corrected/georeferenced image to register an image. If you know the correct location of some pixels in your image you want to register you can simply enter those locations in the Modify Control Point dialog available by clicking on Register dialog->Edit->Modify Controls Points.. menu.

 

You can also register your image from a model. Here is a short video showing a simple the registration of your .jpeg file to a rectangle element around the original position of the .jpeg file.

HTH,

Mathieu

Thanks Mathew,  really appreciate hope u have a great weekend......

dipson

Thanks Mathew,  really appreciate hope u have a great weekend......

dipson

hey thanks Mathew 4 all ur help especially ur video....l was able to georef. d image...bellow is hw i went about it Procedures taken 1, the image to be georef was at the origin position of the design plane 2, i used the nothings n eastings positions of (740500N, 533800E & 740500N, 541800E, & 737500N, 533800E & 737500N, 541800E) points on the image to geo ref 3, So i placed a rectangle around those positions on the design plane (distance frm origin) 4, then i used the Descartes registration model to register the image to those 4 points vertexes on the rectangle 5, i resampled the image, creating a new georef image with d world file option 6, i detached the original image and attached the georef image to d view 7, the attached georef image was at another position, so i had to move it the correct position(position of the rectangle, thereby completing the georeferencing process thank you Mathew for evrytin.....but there are still questions i wanna ask quests are - the image had already been vectorized before this georef process.......i hav georef the image(thereby causing a change in location and size) but the vector data didnt georef wit d image, it is still at the normal position and size. Is there a way to still georef it? cos i tried manually scaling and moving it to d position of the rectangle but it aint fitting properly…or hw shld I go about it -anoda question is dat, i used the 3pts or + affine model to georef the image and it appeared properly.....but y is it dat wen i used the 4pts or + projective model to georef the image, its gave me a blank image, seeing no image -also pls you hav seen d process i used in georef the image, is the a better way to go bout it?, wanna ask u if u have ideas improved ways of goin bout a procedure, or if u hav some tips on hw beta to get done…even if its just one or two thank you again Mathew 4 ur help Regards Dipson

Hi Dipson,

First I find it strange that the geo-referenced image was not located in the rectangle after the registering process. Maybe sister file created was not used according to your Raster Manager related preferences?

Descartes can only geo-reference images. But according to your coordinate you should be able to use standard MicroStation moving and scaling tools to position your vector and your raster correctly without using Bentley Descartes' register tool.

Here is an video showing how to place your raster with some vector on it using standard MicroStation move and scale tool :

Finally for the blank image the 4pts or + projective requires that at least 4 pair of points linearly independent (e.g. : not co-linear) be specified. But according to your coordinates using a projective transformation is not recommended. A 2 pts or + similitude transform should do the trick.

HTH,

Mathieu