Why would drone survey CAD and ecw files be delivered mosaiced?

1097
3
07-24-2017 02:01 AM
Oliver_Burdekin
Occasional Contributor II

I've received the results of a drone survey (photogrammetry. Contours have been produced as .dwg and imagery as .ecw. Looking at the outputs they have been mosaiced (so I have 10 of each file type making up the whole area). The files are small in terms of size and I'm wondering what the reason for this might be. I'm unable to contact the surveyors and so thought I would ask the community.

Ideally I'd like to make them into single files which is fine for the .ecws but with the .dwg contours I need to merge the lines on the mosaic edges. Is there a way to merge adjoining lines (using a tolerance or similar) programatically?

Tags (3)
0 Kudos
3 Replies
XanderBakker
Esri Esteemed Contributor

In case the ends of the contour lines don't match up between the different tiles, surely they hay been processed separately. It is important to revise what has been agreed with the provider in terms of products (formats and specifications). The formats you mentioned ECW and DWG are not the most optimal for usage in a GIS. However, if this is the format you agreed upon, there is little you can do. In case the edges between the tiles don't match, you could ask for them to correct that, since those can be considered as errors and not something a self-respecting provider would deliver to a client. 

Nowadays it is more common to use LiDAR data to get your DTM (and DSM) and to obtain high precision aerial photography or use drones (and applications like Drone2Map) to obtain this data.  

There may be tools to help in matching the ends (like About spatial adjustment edgematching—Help | ArcGIS Desktop ), but this should be a task for the provider IMHO.

Oliver_Burdekin
Occasional Contributor II

The edges do match up perfectly but coming from a GIS background (as opposed to CAD) a single contour (line) should be one feature. Would this make a difference in CAD?

0 Kudos
XanderBakker
Esri Esteemed Contributor

If the edges match up perfectly that is a very good thing and probably the result of processing the entire area as a single project. They may have just tiled the contour lines and aerial imagery as a standard procedure to deliver their products. In case you manage to contact them, you could ask for a single file (before tiling). Still a good thing to revise the requirements regarding the data format of the deliverables for future projects. 

Traditionally CAD was used to create map sheets and in the old days quality was varying a lot (if it looked good in the print out, it was good, lines did not have to match exactly, polygons did not close, etc). 

So a single contour line could be and perhaps should be a single part feature. Sometimes the number of vertices in a single feature is so high that it could be a reason to cut the line in parts. In your case you could try to merge the tiles and use the dissolve tool, using the elevation field as dissolve field and with the unsplit option without making multi part features. If you have multiple features for the same elevation, then those features are not connected (correctly). This could still be valid.