Exception Entities

While designing scenery, it's inevitable that you'll want to replace existing geographic features and objects with scenery that you've designed. The Flight Simulator scenery system includes a built-in strategy to handle this scenario, exception entities. This topic details the different methods you can use to make this strategy work for your particular scenery design. The different methods are based on either seed or object priorities.

In Flight Simulator, overlapping seeds from different BGL databases are assigned priority based on design layer, the seed priority system, seed level (8–13), and seed altitude. For seed priority details, see the topic Seed Priority Rules and Guidelines.

You can manipulate object priorities by using the following:

Geographic range exceptions.
Object exceptions—You can use an EX_OBJ BGL opcode to remove one object. The object you want to remove must be very explicitly defined and can be contained in another BGL file.
Range inclusion—(Use with scenery layers.)You can define what rectangular range a BGL file covers, all scenery on a higher layer is masked.

The following example illustrates one method of excluding an object, object exception.

EX_OBJ macro nhi,nlo,ehi,elo,near_far,cnt1,[cnt2],[cnt3] db4;;00 opcode Exclude OBJ dwnlo;;01 latitude iiii M units dwnhi dwelo;;05 longitude 32-bit pseudo dwehi dbnear_far;;09 xxxxxxx1=exclude near object xxxxxx1x = exclude far object xxxxx1xx = exclude near/far object dbcnt1;;10 byte count lsbyte for 1st obj type dbcnt2;;11 byte count lsbyte for 2nd obj type dbcnt3;;12 byte count lsbyte for 3rd obj type endm

Another method you can use to block existing scenery is range inclusion. You can include a one range inclusion command per BGL file. Only one range inclusion command per BGL file is allowed, and the command must be the first item in the exceptions database. The command specifies a rectangular (north, south, east, west) range that the design area covers.

When the file list is built by the front-end processor, both the inclusion range and scenery layer of the BGL file are included in the file list. When objects are retrieved from the database, the inclusion range and scenery layer are used to filter all objects extracted from the database. If an object is at a higher layer and is within the inclusion bounds, it isn't passed to the BGL system. You can set the inclusion type mask to specify the type of filtering you want. The filters are as follows:

incl_mask_object=0000000000000001b incl_mask_vor=0000000000000010b incl_mask_adf=0000000000000100b incl_mask_com=0000000000001000b

These filters are useful when you want to eliminate an area's visual designs (objects) and replace them with your own designs, while keeping all the navigation aids from the default database intact. The following example shows an inclusion range and type storage in a file list.

;VIRTUAL MEMORY FILE LIST BUFFER STRUCTURE ******************************** FILE_LIST2_ENTRYstruc file_name_fielddw0,0,0,0;000 file_bounds_fielddw0,0,0,0,0,0,0,0;008 file_vor_ptrdw0,0;024 file_vor_lodw0;028 file_vor_hidw0;030 file_seed_level_8dw14 dup(0);032 file_seed_level_15dw0,0;060 file_object_ptrdw0,0;064 file_library_ptrdw0,0;068 file_facilities_ptrdw0,0;072 file_anchor_ptrdw0,0;076 file_com_ptrdw0,0;080 file_adf_ptrdw0,0;084 file_dyn_path_ptrdw0,0;088 file_library_mindw0,0,0,0;092 file_library_maxdw0,0,0,0;100 file_misc_data_ptrdw0,0;108 file_title_descriptiondw0,0;112 file_magvar_ptrdw0,0;116 file_exceptions_ptrdw0,0;120 file_extdb3 dup(0);124 file_pathdb61 dup(0);127 \scenery assumed. not included file_layerdw0;188 layer file_inclusion_typedw0;190 inclusion type (0 if none) file_inclusion_northdw0,0;192 inclusion bound N file_inclusion_southdw0,0;196 inclusion bound S file_inclusion_eastdw0,0;200 inclusion bound E file_inclusion_westdw0,0;204 inclusion bound W file_list_sparesdb48 dup(0);208 file_list_struc_sizedw0;256 FILE_LIST2_ENTRYends

The following example shows the database specification of an inclusion item.

;DATABASE HEADER ******************************************************** dw0001;00 world set number (not saved to file list) dd0004c4eabh;02 N bound 43 degrees meter units dd000400000h;06 S bound dd0cf000000h;10 E bound 85 degrees 32-bit pseudo dd0bf000000h;14 W bound dd0;18 VOR_DATA . . . ddEXCEPTIONS_DATA;114 EXCEPTION LIST PTR (points at exception list) . ;Inclusion Entity Definition inclusion_opcode=3 incl_mask_object=0000000000000001b incl_mask_vor=0000000000000010b incl_mask_adf=0000000000000100b incl_mask_com=0000000000001000b INCLUSION_ITEMstruc inclusion_opdb0 inclusion_maskdw0 inclusion_northdw0,0 inclusion_southdw0,0 inclusion_eastdw0,0 inclusion_westdw0,0 inclusion_item_sizedw0 INCLUSION_ITEMends

;INCLUSION ENTITY OPCODE DEFINITION INCLUSION_RANGE macro nhi,nlo,shi,slo,ehi,elo,whi,wlo,mask db3;;00 op dwmask dwnlo,nhi;;n,s items are 512m/unit

dwslo,shi dwelo,ehi;;e,w items are 16-bit pseudodeg. dwwlo,whi endm

EXCEPTIONS_DATA: rel_base=EXCEPTIONS_DATA INCLUSION_RANGE46h,0fc00h,46h,0fb00h,0c1c3h,0af40h,0c1c3h,0af00h,0003h EOL

The following is an example of a range inclusion opcode that masks objects on lower layers within the defined area.

INCLUSION macro north,south,east,west,mask db3;;00 opcode Exclude OBJ dwmask;;01 inclusion type mask ;; ...............1=objects ;; ..............1.=vors ;; .............1..=adfs ;;............1...=com ddnorth;;03 north M units (inclusive) ddsouth;;07 south M units (inclusive) ddeast;;11 east 32-bit pseudodegrees (inclusive) ddwest;;15 east 32-bit pseudodegrees (inclusive) endm