ChimeraX does not have any options listed on the Open dialog.  It uses a native Open File dialog (Mac, Windows, Linux) and those do not allow adding extra options in the dialog at least when using the Qt window toolkit which ChimeraX uses.  So the "difference" option I added only is available from the ChimeraX command.

        Tom


> On Oct 23, 2023, at 11:21 AM, Tom Goddard <goddard@sonic.net> wrote:
>
> Hi Francisco,
>
>
> Yes, ChimeraX will show positive and negative contour surfaces and avoid making surfaces at the box boundaries above the negative threshold if it knows it is a difference map when it is opened.  There is no way to tell it a map is a difference map, until tomorrow.  I added the option "difference" to the open command for maps so in tomorrow's daily build you could use
>
>       open mymap.mrc diff true
>
> For using earlier ChimeraX versions you can add a negative threshold and turn of the surfaces at the box faces.  To make the negative contour surface ctrl-click on the map histogram and select "New threshold" from the popup menu.  To avoid the surface at the box boundary use command
>
>       volume #1 capFaces false
>
> assuming the map you opened is model #1.  You probably also want to change the colors of the two threshold which you can do by clicking the color button above the histogram, which will color the last histogram level bar you clicked on.  Or you could combine the colors in the above volume command
>
>       volume #1 color green color red capFaces false
>
> You could also make the negative threshold level with the same command
>
>       volume #1 level -1 color green level 1 color red capFaces False
>
> And as Oliver mentioned you can make an alias for this command and put in your ChimeraX startup preferences
>
>       alias diff volume $1 level -1 color green level 1 color red capFaces False
>
> then use
>
>       diff #1
>
>  Tom
>
>> On Oct 23, 2023, at 10:50 AM, Oliver Clarke via ChimeraX-users <chimerax-users@cgl.ucsf.edu> wrote:
>>
>> I think the question is maybe how to set a negative and positive contour for the difference map - this happens automatically if a difference map is loaded from the EDS in Chimera X. Otherwise you have to do it manually. In Chimera I had an alias for this - I haven't yet converted this to ChimeraX syntax, but in case it is useful:
>>
>> #Normalizes map to rms and sets two contours, -3Xrms (red mesh) and 3Xrms (green mesh)
>> #Usage: split_diff_map #map_id_in #map_id_out
>> alias ^split_diff_map vop scale $1 rms 1 modelID $2; close $1; volume $2 capfaces false style mesh meshlighting false squaremesh false level -3 color #da1200000000 level 3 color #0000bda00000; sop cap off; set depthCue; set dcStart 0.2; set dcEnd 1
>>
>>> On Oct 23, 2023, at 1:42 PM, Elaine Meng via ChimeraX-users <chimerax-users@cgl.ucsf.edu> wrote:
>>>
>>> Hi Francisco,
>>> I don't really understand the question.  As I understand it, in ChimeraX all maps are treated the same.  A difference map is still a map, and there is no way to mark it as a "difference" map... and even if there were some way to do so, it wouldn't change how the map is handled or displayed.
>>>
>>> But maybe this question is in reference to ISOLDE?  In that case, I will have to plead ignorance and let somebody else respond.
>>>
>>> Regards,
>>> Elaine
>>> -----
>>> Elaine C. Meng, Ph.D.
>>> UCSF Chimera(X) team
>>> Department of Pharmaceutical Chemistry
>>> University of California, San Francisco
>>>
>>>> On Oct 22, 2023, at 2:00 PM, Francisco Murphy Pérez via ChimeraX-users <chimerax-users@cgl.ucsf.edu> wrote:
>>>>
>>>> When I open a map* in chimerax, how do I specify it is a difference density map?
>>>>
>>>> * maps are generated with `phenix.mtz2map finalpdb.pdb finalmtz.mtz` ... both files from the pdb-redo.
>>>>
>>>> Thanks
>>>
>>>
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>>
>>
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>