无 NONE。NERS 是保留值，不按普通文件名处理；能否取得数据取决于 NERS 的安装和配置。

NONE is not supported. NERS is a reserved value, not an ordinary filename; data availability depends on the NERS installation and configuration.

无 NONE。旧网页中的 DE403_EPHEMERIDES: 不是本版解析器接受的关键词；也不能据本关键词名推断任意 JPL 文件格式都能直接读取。

NONE is not supported. The old DE403_EPHEMERIDES keyword is not accepted by this parser. The generic keyword name does not imply support for every JPL file format.

没有关闭选项；NONE 在此会被当作文件名检查。天线座架类型指地平式（方位—俯仰）、赤道式等轴系形式；轴线偏差指两条旋转轴线不相交时的最短距离。本文件不提供测站三维坐标，坐标由 STATION_COORDINATES 指定。

There is no disabling value: NONE is treated as a filename. Mount type denotes the axis arrangement, such as alt-azimuth or equatorial. Axis offset is the shortest distance between the two non-intersecting rotation axes. Station coordinates are supplied separately by STATION_COORDINATES.

无 NONE。坐标、速度、偏心向量和随时间变化的位置改正是不同输入，不能互相替代。

NONE is not supported. Coordinates, velocities, eccentricity vectors and time-dependent position corrections are separate inputs.

速度的单位依数据文件格式解释；此关键词的值本身是文件名，不是速度数值。

Units are defined by the data-file format. The value of this keyword is a filename, not a numerical velocity.

无 NONE。偏心向量不能与天线固定轴和活动轴之间的轴线偏差混为一谈。

NONE is not supported. A monument-to-antenna eccentricity is distinct from the offset between the fixed and moving antenna axes.

同一 i 的四个关键词应成套提供。使用连续编号最清楚；不要把 NONE 与已配置的索引条目混写，NONE 分支并不逐项清除先前数据。

Supply all four POSVAR keywords for each index. Consecutive numbering is clearest. Do not mix NONE with indexed entries: the NONE branch does not clear previously configured array elements.

i 为 1–16，与其他 POSVAR 条目一致。文档中偶见的 HARMONIC_MODE 少了末尾 L，不是合法值。

i must be 1–16 and match the other POSVAR entries. HARMONIC_MODE, without the final L, is not accepted.

i 为 1–16。该设置主要作用于 TIME_SERIES；周期项模型直接求值，B 样条模型按自身系数求值。不要把它解释为所有模型都会重新做一次所选插值。

i is 1–16. This primarily affects TIME_SERIES. Harmonic models are evaluated directly, and B-spline models use their own coefficients; this does not re-interpolate every model.

i 为 1–16。IF_AVAILABLE 不代表损坏文件、错误格式或任意读取失败都应被忽略。

i is 1–16. IF_AVAILABLE does not mean that malformed files or arbitrary read failures are ignored.

无 NONE。四份射电源表按第 1 至第 4 份顺序读取；同一源在后续文件中的记录可覆盖先前记录。对于太阳系内天体，还需结合目标类型和轨道数据进行计算。

NONE is not supported. Catalogues 1 through 4 are processed in order, and later records for the same source can replace earlier records. This is not a first-match lookup. Near-field sources also depend on their object types and orbit files.

后续文件既可补充新的射电源，也可覆盖前面文件中同名源的坐标或其他信息。

This is not merely a fallback catalogue: a later record for an already encountered source can replace its coordinates or source information.

后续文件既可补充新的射电源，也可覆盖前面文件中同名源的坐标或其他信息。

This is not merely a fallback catalogue: a later record for an already encountered source can replace its coordinates or source information.

后续文件既可补充新的射电源，也可覆盖前面文件中同名源的坐标或其他信息。

This is not merely a fallback catalogue: a later record for an already encountered source can replace its coordinates or source information.

它是对射电源表的补充；各数值的单位与记录格式由该数据文件的读取程序规定。

This supplements the source catalogue. Units and record structure are defined by the corresponding file reader.

“近场”在这里表示计算中需要考虑目标的有限距离，主要涉及太阳系内自然天体及人造卫星、空间探测器等人造天体。仓库文档列出 NZO、CCSDS 轨道消息、TLE 和 SP3 等输入格式；具体支持情况以轨道读取程序为准。设置此路径并不会改变射电源表中记录的目标类型。

Near-field here means that the finite distance of the target must be considered. Typical targets are natural Solar-system bodies, artificial satellites and spacecraft. The repository documentation lists NZO, CCSDS orbit messages, TLE and SP3; actual support is determined by the orbit readers. Setting this path does not change the object types in the source catalogue.

这里通常填写控制文件，不是直接填写一张 FITS 图像。旧文档的 NO 不是本版关闭值。

Supply a control file rather than an individual FITS image. NO in the old documentation is not the disabling value accepted here.

VTD_CONF 只保存模型名称，不检查具体取值；上表列出 VTD_SOU_DEBIAS 实际识别的名称。

MAP/MOD 模型使用源码内置的三次 B 样条系数，按源赤纬求值，再除以有效频率的平方。1MAS 和 10MAS 直接采用指定的赤纬偏差，用于测试。程序先检查观测类型和有效频率，不满足条件时直接返回，因此并非所有观测都会应用改正。

这些改正通过时延对源坐标的偏导数计入理论时延及其变化率，不会直接改写输入射电源表。模型名称中的数字和 N/S/A/R 是内置模型标识，不能据名称自行解释为可调高度等参数。精确定义以源码中的节点和系数表为准；不要使用文档误写的 MAP_850N 等名称。

VTD_CONF stores the name without validating the model. The table lists names recognized by VTD_SOU_DEBIAS.

MAP/MOD models evaluate built-in cubic B-splines at the source declination and divide the result by the effective frequency squared. 1MAS and 10MAS use the specified declination biases for testing. Observable-type and effective-frequency checks can return before a correction is applied.

Corrections enter the theoretical delay and delay rate through source-coordinate partial derivatives; the input source catalogue is not rewritten. Digits and N/S/A/R are built-in model identifiers, not freely adjustable height parameters. The node and coefficient tables define the models precisely. Do not use misspellings such as MAP_850N.

本版 VTD_GAL_ABR 的加速度常量为 2.531×10⁻¹⁰ m/s²，并相对源参考历元计算。它不是视差角 PARALLACTIC_ANGLE；文档中两者有复制文字错误。

This VTD_GAL_ABR implementation uses 2.531×10⁻¹⁰ m/s² and computes the change relative to the source reference epoch. It is distinct from PARALLACTIC_ANGLE; parts of the documentation contain copied text confusing the two.

EOP 时间序列、地球自转先验模型（AEM）、地球自转经验模型（ERM）及地球定向周期项模型（HEO）分别提供不同信息；应按照实际采用的地球自转计算方法配套配置。

Conventional EOP series and the AEM, ERM and harmonic models have distinct roles. Their settings must form a consistent combination.

这是输入 EOP 序列的时间尺度，不能据此改变 VTD 其他 API 参数所要求的时间尺度。

This describes the EOP input epochs. It does not change the time scales required by other VTD API arguments.

AEM 中的参数属于不能忽略其高阶项的大角度量；小的缓变改正和周期性改正分别由 ERM 与 HEO 模型提供。若设置 EOP_TIME_SCALE: NONE，本关键词必须先出现，并且已给出非空 AEM 文件名。

AEM describes large-angle parameters whose higher-order terms cannot be neglected. ERM and HEO supply small slowly varying and periodic corrections, respectively. For EOP_TIME_SCALE: NONE, AEM_FILE must already have supplied a nonempty filename.

地球自转先验模型（AEM）给出基本旋转；ERM 给出缓慢变化的小改正；地球定向周期项模型（HEO）给出周期性小改正。

AEM supplies the large-angle rotation, ERM supplies slowly varying corrections, and the harmonic EOP file supplies periodic corrections.

模型以正弦、余弦项之和表示周期性变化，并可包含振幅和相位的缓慢变化。它与 EOP 时间序列、AEM 地球自转先验模型、ERM 地球自转经验模型的作用不同，是否叠加由所选计算方法决定。

The model represents periodic variations as a sum of sine and cosine terms, allowing slowly varying amplitudes and phases. Its role differs from EOP time series, the AEM a priori rotation and ERM empirical corrections; combination depends on the selected calculation path.

本项决定用哪个模型；模型怎样与 EOP 序列组合，由 UZT_USE 决定。

This selects the model; UZT_USE determines how it is combined with the EOP series.

选择取决于输入 UT1 序列是否已经含有相应潮汐；应避免重复加入或重复去除。

The choice depends on whether the input UT1 series already includes the relevant tide terms. Avoid adding or removing them twice.

正确拼写是 NO_SARG；文档的 NO_SANG 不会被接受。NO_SARG 会改变实际旋转矩阵，不是单纯不输出某个角。

The accepted spelling is NO_SARG, not the documented NO_SANG. NO_SARG changes the rotation matrix; it does not merely suppress an output angle.

NONE 不应被理解为任何计算流程下地球都“没有岁差”：AEM 可以已经包含相应旋转。

NONE does not mean that every calculation path omits physical precession: AEM may already include the corresponding rotation.

实现限制： MHB2000_ADDON 会被 VTD_CONF 接受，但 VTD_ERM_NA 的实际分支没有相应处理，会进入未知章动代码错误。三个 NUT__PET 选项的精确定义应以 heo_empi.f 及其系数表为准，不宜仅凭字母猜测物理模型。

Implementation limit: VTD_CONF accepts MHB2000_ADDON, but VTD_ERM_NA has no corresponding computation branch and reports an unknown nutation code. The precise NUT__PET definitions are given by heo_empi.f and its coefficient tables; the letters alone do not define a standard physical model.

要与所用主章动模型的定义一致，避免重复加入已包含的项。

Keep this consistent with the definition of the main nutation model to avoid adding an included contribution twice.

此处“二阶”对应球谐展开中的 degree 2，表示引潮位展开的相应部分。

Degree 2 is the spherical-harmonic degree; it does not mean squaring the displacement.

本关键词没有 NONE，关闭值必须写 ZERO。永久潮约定应与测站坐标系统相容。

NONE is not accepted: use ZERO to suppress this response. The permanent-tide convention must be consistent with the station coordinates.

模型名称与二阶固体潮共用一套枚举，但作用于极潮；平均极的位置另由 MEAN_POLE_MODEL 控制。

The enumeration is shared with degree-2 solid tides but is applied to pole tides. MEAN_POLE_MODEL separately selects the mean pole.

是否计算极潮由 POLE_TIDE_MODEL 决定；此处改变的是从极移中扣除的平均极。

POLE_TIDE_MODEL controls whether pole tides are computed. This option changes the mean pole subtracted from polar motion.

文件提供焦距变化随仰角的关系，VTD 对其插值并换算为时延改正。未列入文件的天线，其重力形变时延项取零。此项与固体潮位移、天线热膨胀分别处理。

The file supplies focal-length changes as a function of elevation. VTD interpolates them and converts them to delay corrections. An antenna absent from the file receives a zero gravitational-deformation delay contribution. Solid Earth tides and thermal expansion are handled separately.

实现问题： 温度来源的报错分支错误地再次判断 SPD，因此某些非法值未被拒绝；请只使用 METEO 或 SPD。是否检查 SPD 温度数据的可用性还受无关的 IER 条件控制，因此即使配置解析成功，也不能据此确认外部温度数据可用。

Implementation issues: the error branch for the temperature source repeats the SPD test, leaving some invalid values unreported. Use only METEO or SPD. An unrelated IER condition also gates the SPD-data dependency check, so successful configuration parsing does not prove that external temperature data are ready.

轴线偏差数值由 STATION_DESCRIPTION 指定的测站信息文件提供；本关键词只控制计算方式。与大气传播的耦合项由 TROP_AXOF_COUPLING 单独设置。

The offset value comes from the station description; this keyword selects the treatment. A separate keyword controls atmospheric coupling to the offset.

关闭值是 NONE，不是旧文档部分段落所写的 NO。

The disabling value is NONE, not the NO shown in parts of the old documentation.

不能把它当作总对流层时延开关。另受 PARALLACTIC_ANGLE: NONE 的赋值错误影响，见下一条。

This is not the total tropospheric-delay switch. It is also affected by the PARALLACTIC_ANGLE: NONE assignment defect.

确定的赋值错误： NONE 分支没有给 PARALLACTIC_ANGLE 赋值，会意外关闭大气—几何耦合，并造成配置顺序依赖。若先设 YES 再设 NONE，后者也不能可靠撤销前者。

Confirmed assignment defect: the NONE branch does not assign PARALLACTIC_ANGLE. It unexpectedly disables atmospheric–geometric coupling and makes the outcome depend on ordering. A NONE entry following YES also fails to reliably undo that YES setting.

实现不一致： VTD_CONF 把 NONE 清成空串，但 VTD_LOAD_STADESC、VTD_LOAD_NZO 的加载条件比较的是“不是字符串 NONE”。因此空串仍可能进入文件夹扫描；此处记录的是静态控制流风险，没有据此声称已经做过运行复现。旧名 PHASE_OFFSET_FILE 会被兼容预处理改写为 DIR_BTX。

Implementation inconsistency: VTD_CONF clears NONE to an empty string, whereas VTD_LOAD_STADESC and VTD_LOAD_NZO test for a value different from the literal NONE. The empty string can therefore still enter directory scanning. This is a static control-flow finding, not a reported runtime reproduction. The legacy PHASE_OFFSET_FILE name is preprocessed to DIR_BTX.

实际行为： VTD_TROPDEL 在气压超出合理范围时，仅区分 IMA 与其他值，故 NONE 也走 CALC 的气压替代分支。正常范围内的气压不受该回退逻辑改变。

Actual behavior: when pressure is outside its accepted range, VTD_TROPDEL distinguishes only IMA from other values. NONE therefore also takes the CALC pressure fallback. Pressure within the accepted range is not changed by this fallback logic.

SPD_3D 数据可在后续替换先验斜路径时延，所以此处 NONE 不等于整个模型没有大气时延。

SPD_3D may later replace the a priori slant delay. NONE here does not imply the absence of all atmospheric delay.

没有 SAASTAMOINEN、NMFW 或 SPD 这些取值。设置 NONE 仍可通过 SPD_3D 提供总时延及水汽分量，也不妨碍估计残余天顶时延。

SAASTAMOINEN, NMFW and SPD are not values for this keyword. NONE still allows SPD_3D total and water-vapor delays and does not prevent estimation of a residual zenith-delay parameter.

MMF 已被禁用： 解析器接受并检查文件存在，但 VTD_LOAD 明确报错 “obsolete, and it is disabled”。此限制也适用于其他三个带 MMF 的关键词。

MMF is disabled: parsing accepts the option and checks the file, but VTD_LOAD explicitly reports that MMF is obsolete and disabled. The same restriction affects the other three MMF-enabled keywords.

实际用途： 在本次检索的 vtd/src 中，WMF_MODEL 仅由配置解析器赋值，没有在 VTD_TROPDEL 中作为计算分支读取。不能承诺更改此关键词就会改变湿时延或估计偏导。用于残余大气时延估计的映射形式实际由 ATMOSPHERE_PATH_DELAY_PARTIAL 选择。

Actual use: in the inspected vtd/src tree, WMF_MODEL is assigned by the parser but is not read as a computational selector by VTD_TROPDEL. Changing this keyword cannot be promised to change the wet delay or fitted partial. ATMOSPHERE_PATH_DELAY_PARTIAL selects the mapping used for the residual atmospheric-delay parameter.

SPD_3D 依赖 EXTERNAL_DELAY_DIR 系列及各测站的有效数据。VTD_TROPDEL 的外部数据替换分支明确判断 SPD_3D；EXT_PD 虽可解析，不能据此认为它在纯 VTD 调用链中与 SPD_3D 等价，需核对宿主程序如何提供和使用外部时延。

TRP__EXT_3D 是 Fortran 常量名，其值为 EXT_PD；错误信息中的 EXT_3D 不应照抄。兼容关键词 SLANTED_PATH_DELAY_MODEL: 与本关键词同义。

SPD_3D depends on EXTERNAL_DELAY_DIR entries and valid station data. The replacement branch in VTD_TROPDEL explicitly tests SPD_3D. Although EXT_PD parses, it is not equivalent to SPD_3D in the standalone VTD path; inspect how the host program supplies and applies external delays.

TRP__EXT_3D is the Fortran constant name, whose value is EXT_PD. Do not copy EXT_3D from the error message. SLANTED_PATH_DELAY_MODEL is a compatible keyword alias.

实际用途限制： VTD_LOAD_SPD 确实读取并存储这些字段；本次检索的 VTD 主计算流程没有找到对 ZEN_BIAS、ZEN_SCALE 的后续应用，不能把它描述为“填写后必然加上的常数斜路径时延”。兼容名称为 SLANTED_PATH_DELAY_BIAS_FILE。

Actual-use limitation: VTD_LOAD_SPD reads and stores these fields, but no later application of ZEN_BIAS or ZEN_SCALE was found in the inspected VTD main path. A successful read does not prove that a constant slant-delay correction is applied. SLANTED_PATH_DELAY_BIAS_FILE is the compatible alias.

EXTERNAL_DELAY_DIR 指定的文件夹也是 TOTAL_SCALE、WATER_SCALE 依赖检查的对象；仅填写后面三个路径不能满足这一检查。四个路径按顺序用于查找数据，不将四份时延相加；数据须符合所需测站名称、格式和时间范围。

The first directory is also checked as a dependency of TOTAL_SCALE and WATER_SCALE; directories 2–4 alone do not satisfy that check. The four directories do not define four delays to be added together. Data must satisfy the required station, format and time coverage.

前面的文件夹未找到所需测站的可用数据时，再查找此文件夹。四个路径按顺序用于查找数据，不将四份时延相加；数据须符合所需测站名称、格式和时间范围。

This directory is searched when usable station data have not been found in preceding directories. The four directories do not define four delays to be added together. Data must satisfy the required station, format and time coverage.

前面的文件夹未找到所需测站的可用数据时，再查找此文件夹。四个路径按顺序用于查找数据，不将四份时延相加；数据须符合所需测站名称、格式和时间范围。

This directory is searched when usable station data have not been found in preceding directories. The four directories do not define four delays to be added together. Data must satisfy the required station, format and time coverage.

前面的文件夹未找到所需测站的可用数据时，再查找此文件夹。四个路径按顺序用于查找数据，不将四份时延相加；数据须符合所需测站名称、格式和时间范围。

This directory is searched when usable station data have not been found in preceding directories. The four directories do not define four delays to be added together. Data must satisfy the required station, format and time coverage.

TOTAL_SCALE、WATER_SCALE 要求第一外部时延文件夹非空，并应配合 SPD_3D 及相应分量数据；解析器只检查文件夹条件，不能验证完整模型组合。

GAUSSIAN_LAYER 存在确定的读字段错误： 第三个字段被同时读入高度和宽度，第四个字段没有被正确使用。例如 GAUSSIAN_LAYER 5000.0 500.0 实际把两者都读成 5000.0。修正前不能据配置文本认为采用了 500 m 的 FWHM。两个数的读取格式是 F12.6，务必写小数点。

IONO_* 在这里仅借用薄壳的仰角依赖形式，并不会自动启用 TEC 电离层时延。

TOTAL_SCALE and WATER_SCALE require a nonempty first external-delay directory and should be paired with SPD_3D and the required data components. The parser checks the directory condition, not the entire model combination.

Confirmed GAUSSIAN_LAYER field-reading defect: both height and width are read from field 3; field 4 is not correctly used. Thus GAUSSIAN_LAYER 5000.0 500.0 reads 5000.0 for both values. Until corrected, the text cannot be taken as selecting a 500 m FWHM. Both reads use F12.6: include a decimal point.

IONO_* only borrows the thin-shell elevation dependence here; it does not enable a TEC-based ionospheric delay.

e 为仰角，A 为方位角，C_CH 为源码常数 C__CHEN_HERRING；偏导数的正负号取决于参数定义。本关键词只选择偏导数形式，不提供先验梯度数值，也不指定参数估计结果。

e is elevation, A is azimuth and C_CH is the source constant C__CHEN_HERRING. Signs depend on the parameter definition. This keyword selects partial derivatives; it supplies neither a priori gradient values nor estimated gradient results.

后两者是在映射函数中改变高度和角度关系；VTD_IONO_DELAY 的穿刺点计算仍读取 TEC 文件头高度，不能概括为“所有几何量都改用 506.7 或 600 km”。时延还取决于观测频率、观测类型及 IONOSPHERE_SCALE。最后是否把该项加入总时延，还受调用方 OBS_TYP%APPLY_IONO 控制。

The last two choices change the height and angle relation in the mapping function. Pierce-point geometry in VTD_IONO_DELAY still uses the TEC header height, so not all geometry moves to 506.7 or 600 km. The result also depends on observing frequency, observable type and IONOSPHERE_SCALE. The caller’s OBS_TYP%APPLY_IONO controls whether the contribution is added to total delay.

解析器没有设置数值上下限，能读入负值不代表它具有通常物理意义。环境变量 VTD_IONO_SCALE 能在计算中覆盖配置值；检查结果时应同时检查该环境变量。

No numerical bounds are enforced. Acceptance of a negative number does not imply its usual physical suitability. The VTD_IONO_SCALE environment variable can override the configured value during computation.

VTD_LOAD_IONO 依次查找首个覆盖整个所需时段的文件，找到后停止；不把九个文件的时延相加，也不是自动按日期拼接九个文件。原始 IONEX 文本不能仅改扩展名就作为 VIONO 使用。

VTD_LOAD_IONO selects the first file covering the entire requested interval, then stops. It neither adds nine ionospheric delays nor automatically concatenates the nine files by date. Renaming an IONEX text file does not convert it to VIONO.

VTD_LOAD_IONO 依次查找首个覆盖整个所需时段的文件，找到后停止；不把九个文件的时延相加，也不是自动按日期拼接九个文件。原始 IONEX 文本不能仅改扩展名就作为 VIONO 使用。

VTD_LOAD_IONO selects the first file covering the entire requested interval, then stops. It neither adds nine ionospheric delays nor automatically concatenates the nine files by date. Renaming an IONEX text file does not convert it to VIONO.

VTD_LOAD_IONO 依次查找首个覆盖整个所需时段的文件，找到后停止；不把九个文件的时延相加，也不是自动按日期拼接九个文件。原始 IONEX 文本不能仅改扩展名就作为 VIONO 使用。

VTD_LOAD_IONO selects the first file covering the entire requested interval, then stops. It neither adds nine ionospheric delays nor automatically concatenates the nine files by date. Renaming an IONEX text file does not convert it to VIONO.

VTD_LOAD_IONO 依次查找首个覆盖整个所需时段的文件，找到后停止；不把九个文件的时延相加，也不是自动按日期拼接九个文件。原始 IONEX 文本不能仅改扩展名就作为 VIONO 使用。

VTD_LOAD_IONO selects the first file covering the entire requested interval, then stops. It neither adds nine ionospheric delays nor automatically concatenates the nine files by date. Renaming an IONEX text file does not convert it to VIONO.

VTD_LOAD_IONO 依次查找首个覆盖整个所需时段的文件，找到后停止；不把九个文件的时延相加，也不是自动按日期拼接九个文件。原始 IONEX 文本不能仅改扩展名就作为 VIONO 使用。

VTD_LOAD_IONO selects the first file covering the entire requested interval, then stops. It neither adds nine ionospheric delays nor automatically concatenates the nine files by date. Renaming an IONEX text file does not convert it to VIONO.

VTD_LOAD_IONO 依次查找首个覆盖整个所需时段的文件，找到后停止；不把九个文件的时延相加，也不是自动按日期拼接九个文件。原始 IONEX 文本不能仅改扩展名就作为 VIONO 使用。

VTD_LOAD_IONO selects the first file covering the entire requested interval, then stops. It neither adds nine ionospheric delays nor automatically concatenates the nine files by date. Renaming an IONEX text file does not convert it to VIONO.

VTD_LOAD_IONO 依次查找首个覆盖整个所需时段的文件，找到后停止；不把九个文件的时延相加，也不是自动按日期拼接九个文件。原始 IONEX 文本不能仅改扩展名就作为 VIONO 使用。

VTD_LOAD_IONO selects the first file covering the entire requested interval, then stops. It neither adds nine ionospheric delays nor automatically concatenates the nine files by date. Renaming an IONEX text file does not convert it to VIONO.

VTD_LOAD_IONO 依次查找首个覆盖整个所需时段的文件，找到后停止；不把九个文件的时延相加，也不是自动按日期拼接九个文件。原始 IONEX 文本不能仅改扩展名就作为 VIONO 使用。

VTD_LOAD_IONO selects the first file covering the entire requested interval, then stops. It neither adds nine ionospheric delays nor automatically concatenates the nine files by date. Renaming an IONEX text file does not convert it to VIONO.

VTD_LOAD_IONO 依次查找首个覆盖整个所需时段的文件，找到后停止；不把九个文件的时延相加，也不是自动按日期拼接九个文件。原始 IONEX 文本不能仅改扩展名就作为 VIONO 使用。

VTD_LOAD_IONO selects the first file covering the entire requested interval, then stops. It neither adds nine ionospheric delays nor automatically concatenates the nine files by date. Renaming an IONEX text file does not convert it to VIONO.

实现不一致： ITRF1996 被赋为 VTD__METRIC_ITRF1992；VTD_PK2001 对 ITRF1992 与 ITRF1996 设有不同分支，所以不能把该文本值当作已正确执行 ITRF1996 计算。它也不是“选取某一版测站坐标表”的关键词。

Implementation mismatch: ITRF1996 is assigned VTD__METRIC_ITRF1992. VTD_PK2001 has distinct ITRF1992 and ITRF1996 branches, so the text does not correctly select the latter. This is not a keyword for selecting a station-coordinate catalogue release.

无 NONE。远场或近场计算由源类型等信息决定，不是仅写这个关键词就把某源强制归为远场。

NONE is not supported. The source type and related data determine whether the far- or near-field path is used; this keyword alone does not classify a source as far-field.

无 NONE。近场计算还依赖目标轨道、时刻和源类型；不能只更改此值就得到卫星时延。

NONE is not supported. Near-field calculations also require the target orbit, epoch and source type; changing this value alone does not produce a satellite delay.

本版唯一合法枚举值；没有 NONE。它设置的是多普勒计算方法，不等于要求 VTD_DELAY 每次都输出多普勒，也不同于 DELAY_RATE。

This is the only supported enumeration value; NONE is not accepted. Selecting a Doppler method does not make every VTD_DELAY call return a Doppler result, and it is distinct from DELAY_RATE.

NONE 不应被解释为可以把全部返回的时延率字段当作已严格清零；下游是否读取这些字段仍需遵守接口用法。

相关实现问题： VTD_DELAY 汇总 RATE 时先无条件加入两站电离层时延率差，随后在 OBS_TYP%APPLY_IONO 为真时再次加入同一差值。电离层时延率非零时会有重复计入风险；不能仅凭 DELAY_RATE: YES 就认为所有时延率项已经正确汇总。

NONE does not guarantee that every returned rate field has been explicitly zeroed; downstream consumers must respect the interface contract.

Related implementation issue: VTD_DELAY first adds the station ionospheric-rate difference unconditionally when forming RATE, then adds the same difference again when OBS_TYP%APPLY_IONO is true. Nonzero ionospheric rates can therefore be counted twice. DELAY_RATE: YES alone does not ensure correct aggregation of every rate term.

进入与 SLANT_PATH_DELAY_MODEL 相同的解析分支。使用 NONE、SPD_3D 或 EXT_PD。 其模型限制与对应常规关键词相同。

Uses the same parser branch as SLANT_PATH_DELAY_MODEL. Values are NONE, SPD_3D and EXT_PD. The canonical keyword’s model limitations still apply.

进入与 SLANT_PATH_DELAY_BIAS_FILE 相同的解析分支。值为文件名或 NONE。 其模型限制与对应常规关键词相同。

Uses the same parser branch as SLANT_PATH_DELAY_BIAS_FILE. Supply a filename or NONE. The canonical keyword’s model limitations still apply.

在分词和大写转换前，以固定列字符串替换为 DIR_BTX。旧名应从首列大写书写，冒号后留空格；优先使用 DIR_BTX。当前应填写相位中心数据所在的文件夹路径。 其模型限制与对应常规关键词相同。

Rewritten to DIR_BTX by a fixed-column match before tokenization and uppercase conversion. If retained, write the uppercase name in column 1 with a space after the colon. Prefer DIR_BTX. The value now denotes the directory containing phase-center data. The canonical keyword’s model limitations still apply.